Gravitational waves are expected to be produced from neutron star oscillations associated with magnetar giant flares and short bursts. We present the results of a search for short-duration (milliseconds to seconds) and long-duration (∼100 s) transient gravitational waves from 13 magnetar short bursts observed during Advanced LIGO, Advanced Virgo, and KAGRA's third observation run. These 13 bursts come from two magnetars, SGR 1935+2154 and Swift J1818.0−1607. We also include three other electromagnetic burst events detected by Fermi-GBM which were identified as likely coming from one or more magnetars, but they have no association with a known magnetar. No magnetar giant flares were detected during the analysis period. We find no evidence of gravitational waves associated with any of these 16 bursts. We place upper limits on the rms of the integrated incident gravitational-wave strain that reach 3.6 × 10−23/√Hz at 100 Hz for the short-duration search and 1.1 × 10−22/√Hz at 450 Hz for the long-duration search. For a ringdown signal at 1590 Hz targeted by the short-duration search the limit is set to 2.3 × 10−22√Hz. Using the estimated distance to each magnetar, we derive upper limits on the emitted gravitational-wave energy of 1.5 × 1044 erg (1.0 × 1044 erg) for SGR 1935+2154 and 9.4 × 1043 erg (1.3 × 1044 erg) for Swift J1818.0−1607, for the short-duration (long-duration) search. Assuming isotropic emission of electromagnetic radiation of the burst fluences, we constrain the ratio of gravitational-wave energy to electromagnetic energy for bursts from SGR 1935+2154 with the available fluence information. The lowest of these ratios is 4.5 × 103.
Publications
2025
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“Improving cosmological reach of a gravitational wave observatory using Deep Loop Shaping”, Science (2025).
Jonas Buchli, Brendan Tracey, Tomislav Andric, Christopher Wipf, and Yu Him Justin Chiu, et al.Abstract
Improved low-frequency sensitivity of gravitational wave observatories would unlock study of intermediate-mass black hole mergers and binary black hole eccentricity and provide early warnings for multimessenger observations of binary neutron star mergers. Today's mirror stabilization control injects harmful noise, constituting a major obstacle to sensitivity improvements. We eliminated this noise through Deep Loop Shaping, a reinforcement learning method using frequency domain rewards. We proved our methodology on the LIGO Livingston Observatory (LLO). Our controller reduced control noise in the 10- to 30-hertz band by over 30x and up to 100x in subbands, surpassing the design goal motivated by the quantum limit. These results highlight the potential of Deep Loop Shaping to improve current and future gravitational wave observatories and, more broadly, instrumentation and control systems.
Full text · DOI: 10.1126/science.adw1291
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“GW250114: Testing Hawking's Area Law and the Kerr Nature of Black Holes”, Physical Review Letters (2025).
A. G. Abac, I. Abouelfettouh, F. Acernese, K. Ackley, and C. Adamcewicz, et al.Abstract
The gravitational-wave signal GW250114 was observed by the two LIGO detectors with a network matched-filter signal-to-noise ratio of 80. The signal was emitted by the coalescence of two black holes with near-equal masses m₁ = 33.6_(−0.8)^(+1.2)M⊙ and m₂ = 32.2_(−1.3)^(+0.8)M⊙, and small spins χ1,2 ≤ 0.26 (90% credibility) and negligible eccentricity e ≤ 0.03. Postmerger data excluding the peak region are consistent with the dominant quadrupolar (ℓ = |m| = 2) mode of a Kerr black hole and its first overtone. We constrain the modes' frequencies to ±30% of the Kerr spectrum, providing a test of the remnant's Kerr nature. We also examine Hawking's area law, also known as the second law of black hole mechanics, which states that the total area of the black hole event horizons cannot decrease with time. A range of analyses that exclude up to five of the strongest merger cycles confirm that the remnant area is larger than the sum of the initial areas to high credibility.
Full text · DOI: 10.1103/kw5g-d732
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“GW241011 and GW241110: Exploring Binary Formation and Fundamental Physics with Asymmetric, High-spin Black Hole Coalescences”, Astrophysical Journal Letters (2025).
A. G. Abac, I. Abouelfettouh, F. Acernese, K. Ackley, and C. Adamcewicz, et al.Abstract
We report the observation of gravitational waves from two binary black hole coalescences during the fourth observing run of the LIGO–Virgo–KAGRA detector network, GW241011 and GW241110. The sources of these two signals are characterized by rapid and precisely measured primary spins, nonnegligible spin–orbit misalignment, and unequal mass ratios between their constituent black holes. These properties are characteristic of binaries in which the more massive object was itself formed from a previous binary black hole merger and suggest that the sources of GW241011 and GW241110 may have formed in dense stellar environments in which repeated mergers can take place. As the third-loudest gravitational-wave event published to date, with a median network signal-to-noise ratio of 36.0, GW241011 furthermore yields stringent constraints on the Kerr nature of black holes, the multipolar structure of gravitational-wave generation, and the existence of ultralight bosons within the mass range 10−13–10−12 eV.
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“GW231123: A Binary Black Hole Merger with Total Mass 190–265 M⊙”, Astrophysical Journal Letters (2025).
A. G. Abac, I. Abouelfettouh, F. Acernese, K. Ackley, and C. Adamcewicz, et al.Abstract
On 2023 November 23, the two LIGO observatories both detected GW231123, a gravitational-wave signal consistent with the merger of two black holes with masses 137_(−18)^(+23) M⊙ and 101_(−50)+^(+22) M⊙ (90% credible intervals), at a luminosity distance of 0.7–4.1 Gpc, a redshift of 0.40_(−0.25)^(+0.27), and with a network signal-to-noise ratio of ∼20.7. Both black holes exhibit high spins— 0.90_(−0.19)^(+0.10) and 0.80_(−0.52)^(+0.20), respectively. A massive black hole remnant is supported by an independent ringdown analysis. Some properties of GW231123 are subject to large systematic uncertainties, as indicated by differences in the inferred parameters between signal models. The primary black hole lies within or above the theorized mass gap where black holes between 60–130 M⊙ should be rare, due to pair-instability mechanisms, while the secondary spans the gap. The observation of GW231123 therefore suggests the formation of black holes from channels beyond standard stellar collapse and that intermediate-mass black holes of mass ∼200 M⊙ form through gravitational-wave-driven mergers.
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“Digital Discovery of Interferometric Gravitational Wave Detectors”, Physical Review X (2025).
Mario Krenn, Yehonathan Drori, and Rana X. AdhikariAbstract
Gravitational waves, detected a century after they were first theorized, are space-time distortions caused by some of the most cataclysmic events in the Universe, including black hole mergers and supernovae. The successful detection of these waves has been made possible by ingenious detectors designed by human experts. Beyond these successful designs, the vast space of experimental configurations remains largely unexplored, offering an exciting territory potentially rich in innovative and unconventional detection strategies. Here, we demonstrate an intelligent computational strategy to explore this enormous space, discovering unorthodox topologies for gravitational wave detectors that significantly outperform the currently best-known designs under realistic experimental constraints. This increases the potentially observable volume of the Universe by up to 50-fold. Moreover, by analyzing the best solutions from our superhuman algorithm, we uncover entirely new physics ideas at their core. At a bigger picture, our methodology can readily be extended to AI-driven design of experiments across wide domains of fundamental physics, opening fascinating new windows into the Universe.
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“Advanced LIGO detector performance in the fourth observing run”, Physical Review D (2025).
E. Capote, W. Jia, N. Aritomi, M. Nakano, and V. Xu, et al.Abstract
On May 24, 2023, the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO), joined by the Advanced Virgo and KAGRA detectors, began the fourth observing run for a two-year-long dedicated search for gravitational waves. The LIGO Hanford and Livingston detectors have achieved an unprecedented sensitivity to gravitational waves, with an angle-averaged median range to binary neutron star mergers of 152 and 160 Mpc, and duty cycles of 65.0% and 71.2%, respectively, with a coincident duty cycle of 52.6%. The maximum range achieved by the LIGO Hanford detector is 165 Mpc and the LIGO Livingston detector 177 Mpc, both achieved during the second part of the fourth observing run. For the fourth run, the quantum-limited sensitivity of the detectors was increased significantly due to the higher intracavity power from laser system upgrades and replacement of core optics, and from the addition of a 300 m filter cavity to provide the squeezed light with a frequency-dependent squeezing angle, part of the A+ upgrade program. Altogether, the A+ upgrades led to reduced detector-wide losses for the squeezed vacuum states of light which, alongside the filter cavity, enabled broadband quantum noise reduction of up to 5.2 dB at the Hanford observatory and 6.1 dB at the Livingston observatory. Improvements to sensors and actuators as well as significant controls commissioning increased low frequency sensitivity. This paper details these instrumental upgrades, analyzes the noise sources that limit detector sensitivity, and describes the commissioning challenges of the fourth observing run.
2024
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“Search for Gravitational-wave Transients Associated with Magnetar Bursts in Advanced LIGO and Advanced Virgo Data from the Third Observing Run”, Astrophysical Journal (2024).
R. Abbott, H. Abe, F. Acernese, K. Ackley, and N. Adhikari, et al.Abstract
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“Quantum Precision Limits of Displacement Noise-Free Interferometers”, Physical Review Letters (2024).
Tuvia Gefen, Rajashik Tarafder, Rana X. Adhikari, and Yanbei ChenAbstract
Current laser-interferometric gravitational wave detectors suffer from a fundamental limit to their precision due to the displacement noise of optical elements contributed by various sources. Several schemes for displacement noise-free interferometers (DFI) have been proposed to mitigate their effects. The idea behind these schemes is similar to decoherence-free subspaces in quantum sensing; i.e., certain modes contain information about the gravitational waves but are insensitive to the mirror motion (displacement noise). We derive quantum precision limits for general DFI schemes, including optimal measurement basis and optimal squeezing schemes. We introduce a triangular cavity DFI scheme and apply our general bounds to it. Precision analysis of this scheme with different noise models shows that the DFI property leads to interesting sensitivity profiles and improved precision due to noise mitigation and larger gain from squeezing.
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“Observation of Gravitational Waves from the Coalescence of a 2.5–4.5 M⊙ Compact Object and a Neutron Star”, Astrophysical Journal Letters (2024).
A. G. Abac, R. Abbott, I. Abouelfettouh, F. Acernese, and K. Ackley, et al.Abstract
We report the observation of a coalescing compact binary with component masses 2.5–4.5 M⊙ and 1.2–2.0 M⊙ (all measurements quoted at the 90% credible level). The gravitational-wave signal GW230529_181500 was observed during the fourth observing run of the LIGO–Virgo–KAGRA detector network on 2023 May 29 by the LIGO Livingston observatory. The primary component of the source has a mass less than 5 M⊙ at 99% credibility. We cannot definitively determine from gravitational-wave data alone whether either component of the source is a neutron star or a black hole. However, given existing estimates of the maximum neutron star mass, we find the most probable interpretation of the source to be the coalescence of a neutron star with a black hole that has a mass between the most massive neutron stars and the least massive black holes observed in the Galaxy. We provisionally estimate a merger rate density of 55^(+127)_(-47) Gpc⁻³ yr ⁻¹ for compact binary coalescences with properties similar to the source of GW230529_181500; assuming that the source is a neutron star–black hole merger, GW230529_181500-like sources may make up the majority of neutron star–black hole coalescences. The discovery of this system implies an increase in the expected rate of neutron star–black hole mergers with electromagnetic counterparts and provides further evidence for compact objects existing within the purported lower mass gap.
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“Global optimization of multilayer dielectric coatings for precision measurements”, Optics Express (2024).
Gautam Venugopalan, Francisco Salces-Cárcoba, Koji Arai, and Rana X. AdhikariAbstract
We describe the design of optimized multilayer dielectric coatings for precision laser interferometry. By setting up an appropriate cost function and then using a global optimizer to find a minimum in the parameter space, we were able to realize coating designs that meet the design requirements for spectral reflectivity, thermal noise, absorption, and tolerances to coating fabrication errors. We also present application of a Markov-Chain Monte Carlo (MCMC) based parameter estimation algorithm that can infer thicknesses of dielectric layers in a coating, given a measurement of the spectral reflectivity. This technique can be a powerful diagnostic tool for both commercial coating manufacturers, and the community using dielectric mirrors for precision metrology experiments.
Full text · DOI: 10.1364/oe.513807
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“Effects of mirror birefringence and its fluctuations to laser interferometric gravitational wave detectors”, Physical Review D (2024).
Yuta Michimura, Haoyu Wang, Francisco Salces-Carcoba, Christopher Wipf, Aidan Brooks, Koji Arai, and Rana X. AdhikariAbstract
Crystalline materials are promising candidates as substrates or high-reflective coatings of mirrors to reduce thermal noises in future laser interferometric gravitational wave detectors. However, birefringence of such materials could degrade the sensitivity of gravitational wave detectors, not only because it can introduce optical losses, but also because its fluctuations create extra phase noise in the arm cavity reflected beam. In this paper, we analytically estimate the effects of birefringence and its fluctuations in the mirror substrate and coating for gravitational wave detectors. Our calculations show that the requirements for the birefringence fluctuations in silicon substrate and AlGaAs coating will be on the order of 10⁻⁸ and 10⁻¹⁰ rad/√Hz at 100 Hz, respectively, for future gravitational wave detectors. We also point out that optical cavity response needs to be carefully taken into account to estimate optical losses from depolarization.
2023
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“Population of Merging Compact Binaries Inferred Using Gravitational Waves through GWTC-3”, Physical Review X (2023).
R. Abbott, T. D. Abbott, F. Acernese, K. Ackley, and C. Adams, et al.Abstract
We report on the population properties of compact binary mergers inferred from gravitational-wave observations of these systems during the first three LIGO-Virgo observing runs. The Gravitational-Wave Transient Catalog 3 (GWTC-3) contains signals consistent with three classes of binary mergers: binary black hole, binary neutron star, and neutron star–black hole mergers. We infer the binary neutron star merger rate to be between 10 and 1700 Gpc⁻³ yr⁻¹ and the neutron star–black hole merger rate to be between 7.8 and 140 Gpc⁻³ yr⁻¹, assuming a constant rate density in the comoving frame and taking the union of 90% credible intervals for methods used in this work. We infer the binary black hole merger rate, allowing for evolution with redshift, to be between 17.9 and 44 Gpc⁻³ yr⁻¹ at a fiducial redshift (z = 0.2). The rate of binary black hole mergers is observed to increase with redshift at a rate proportional to (1 + z)_κ with κ = 2.9⁺¹⋅⁷₋₁.₈ for z ≲ 1. Using both binary neutron star and neutron star–black hole binaries, we obtain a broad, relatively flat neutron star mass distribution extending from 1.2⁺⁰⋅¹₋₀.₂ to 2.0⁺⁰⋅³₋₀.₃ M_⊙. We confidently determine that the merger rate as a function of mass sharply declines after the expected maximum neutron star mass, but cannot yet confirm or rule out the existence of a lower mass gap between neutron stars and black holes. We also find the binary black hole mass distribution has localized over- and underdensities relative to a power-law distribution, with peaks emerging at chirp masses of 8.3⁺⁰⋅³₋₀.₅ and 27.9⁺¹⋅⁹₋₁.₈ M_⊙. While we continue to find that the mass distribution of a binary's more massive component strongly decreases as a function of primary mass, we observe no evidence of a strongly suppressed merger rate above approximately 60 M_⊙, which would indicate the presence of a upper mass gap. Observed black hole spins are small, with half of spin magnitudes below χᵢ ≈ 0.25. While the majority of spins are preferentially aligned with the orbital angular momentum, we infer evidence of antialigned spins among the binary population. We observe an increase in spin magnitude for systems with more unequal-mass ratio. We also observe evidence of misalignment of spins relative to the orbital angular momentum.
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“Performance of the KAGRA detector during the first joint observation with GEO 600 (O3GK)”, Progress of Theoretical and Experimental Physics (2023).
H Abe, R X Adhikari, T Akutsu, M Ando, and A Araya, et al.Abstract
KAGRA, the kilometer-scale underground gravitational-wave detector, is located at Kamioka, Japan. In April 2020, an astrophysics observation was performed at the KAGRA detector in combination with the GEO 600 detector; this observation operation is called O3GK. The optical configuration in O3GK is based on a power-recycled Fabry–Pérot–Michelson interferometer; all the mirrors were set at room temperature. The duty factor of the operation was approximately 53%, and the displacement sensitivity was approximately 1 × 10⁻¹⁸ m/√Hz at 250 Hz. The binary-neutron-star (BNS) inspiral range was about 0.6 Mpc. The contributions of various noise sources to the sensitivity of O3GK were investigated to understand how the observation range could be improved; this study is called a "noise budget". According to our noise budget, the measured sensitivity could be approximated by adding up the effect of each noise. The sensitivity was dominated by noise from the sensors used for local controls of the vibration isolation systems, acoustic noise, shot noise, and laser frequency noise. Further, other noise sources that did not limit the sensitivity were investigated. This paper provides a detailed account of the KAGRA detector in O3GK, including interferometer configuration, status, and noise budget. In addition, strategies for future sensitivity improvements, such as hardware upgrades, are discussed.
Full text · DOI: 10.1093/ptep/ptac093
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“GWTC-3: Compact Binary Coalescences Observed by LIGO and Virgo during the Second Part of the Third Observing Run”, Physical Review X (2023).
R. Abbott, T. D. Abbott, F. Acernese, K. Ackley, and C. Adams, et al.Abstract
The third Gravitational-Wave Transient Catalog (GWTC-3) describes signals detected with Advanced LIGO and Advanced Virgo up to the end of their third observing run. Updating the previous GWTC-2.1, we present candidate gravitational waves from compact binary coalescences during the second half of the third observing run (O3b) between 1 November 2019, 15∶00 Coordinated Universal Time (UTC) and 27 March 2020, 17∶00 UTC. There are 35 compact binary coalescence candidates identified by at least one of our search algorithms with a probability of astrophysical origin p_(astro) > 0.5. Of these, 18 were previously reported as low-latency public alerts, and 17 are reported here for the first time. Based upon estimates for the component masses, our O3b candidates with p_(astro) > 0.5 are consistent with gravitational-wave signals from binary black holes or neutron-star–black-hole binaries, and we identify none from binary neutron stars. However, from the gravitational-wave data alone, we are not able to measure matter effects that distinguish whether the binary components are neutron stars or black holes. The range of inferred component masses is similar to that found with previous catalogs, but the O3b candidates include the first confident observations of neutron-star–black-hole binaries. Including the 35 candidates from O3b in addition to those from GWTC-2.1, GWTC-3 contains 90 candidates found by our analysis with p_(astro) > 0.5 across the first three observing runs. These observations of compact binary coalescences present an unprecedented view of the properties of black holes and neutron stars.
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“Broadband Quantum Enhancement of the LIGO Detectors with Frequency-Dependent Squeezing”, Physical Review X (2023).
D. Ganapathy, W. Jia, M. Nakano, V. Xu, and N. Aritomi, et al.Abstract
Quantum noise imposes a fundamental limitation on the sensitivity of interferometric gravitational-wave detectors like LIGO, manifesting as shot noise and quantum radiation pressure noise. Here, we present the first realization of frequency-dependent squeezing in full-scale gravitational-wave detectors, resulting in the reduction of both shot noise and quantum radiation pressure noise, with broadband detector enhancement from tens of hertz to several kilohertz. In the LIGO Hanford detector, squeezing reduced the detector noise amplitude by a factor of 1.6 (4.0 dB) near 1 kHz; in the Livingston detector, the noise reduction was a factor of 1.9 (5.8 dB). These improvements directly impact LIGO's scientific output for high-frequency sources (e.g., binary neutron star postmerger physics). The improved low-frequency sensitivity, which boosted the detector range by 15%–18% with respect to no squeezing, corresponds to an increase in the astrophysical detection rate of up to 65%. Frequency-dependent squeezing was enabled by the addition of a 300-meter-long filter cavity to each detector as part of the LIGO A+ upgrade.
2022
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“Using silicon disk resonators to measure mechanical losses caused by an electric field”, Review of Scientific Instruments (2022).
Y. Yu. Klochkov, L. G. Prokhorov, M. S. Matiushechkina, R. X. Adhikari, and V. P. MitrofanovAbstract
Several projects of the next generation gravitational-wave detectors use the high purity monocrystalline silicon test masses. The electric field of the actuator that is applied to correct the position of the silicon test mass causes additional mechanical losses and associated noise. Disk mechanical resonators are widely used to study mechanical losses in multilayer optical coatings that are deposited on the test masses of gravitational-wave detectors. We use silicon disk resonators to study losses caused by an electric field. In particular, the dependence of mechanical losses on the resistivity of silicon is investigated. The resonator is a thin commercial silicon wafer in which a low frequency nodal diameter mode is excited. A DC voltage is applied between the wafer and a nearby electrode. We use two measurement configurations. In the first configuration, the dependence of losses on the resistance in the voltage supply circuit is investigated. The dependence of losses on the resistivity of silicon is investigated in the second configuration. We propose a model that relates the electric field induced mechanical loss in disk resonators to the resistivity of the material. Measurements are carried out for low and high resistivity silicon wafers. The measurement results are compared with calculations. Based on these studies, it is possible to estimate the loss and noise of the test masses of gravitational-wave detectors associated with electrostatic actuators.
Full text · DOI: 10.1063/5.0076311
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“The science case for LIGO-India”, Classical and Quantum Gravity (2022).
M. Saleem, Javed Rana, V. Gayathri, Aditya Vijaykumar, Srashti Goyal, Surabhi Sachdev, Jishnu Suresh, S. Sudhagar, Arunava Mukherjee, Gurudatt Gaur, Bangalore Sathyaprakash, Archana Pai, Rana X. Adhikari, P. Ajith, and Sukanta BoseAbstract
The global network of gravitational-wave detectors has completed three observing runs with ∼50 detections of merging compact binaries. A third LIGO detector, with comparable astrophysical reach, is to be built in India (LIGO-Aundha) and expected to be operational during the latter part of this decade. Such additions to the network increase the number of baselines and the network SNR of GW events. These enhancements help improve the sky-localization of those events. Multiple detectors simultaneously in operation will also increase the baseline duty factor, thereby, leading to an improvement in the detection rates and, hence, the completeness of surveys. In this paper, we quantify the improvements due to the expansion of the LIGO global network in the precision with which source properties will be measured. We also present examples of how this expansion will give a boost to tests of fundamental physics.
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“Searches for Gravitational Waves from Known Pulsars at Two Harmonics in the Second and Third LIGO-Virgo Observing Runs”, Astrophysical Journal (2022).
R. Abbott, H. Abe, F. Acernese, K. Ackley, and N. Adhikari, et al.Abstract
We present a targeted search for continuous gravitational waves (GWs) from 236 pulsars using data from the third observing run of LIGO and Virgo (O3) combined with data from the second observing run (O2). Searches were for emission from the l = m = 2 mass quadrupole mode with a frequency at only twice the pulsar rotation frequency (single harmonic) and the l = 2, m = 1, 2 modes with a frequency of both once and twice the rotation frequency (dual harmonic). No evidence of GWs was found, so we present 95% credible upper limits on the strain amplitudes h 0 for the single-harmonic search along with limits on the pulsars' mass quadrupole moments Q 22 and ellipticities ε. Of the pulsars studied, 23 have strain amplitudes that are lower than the limits calculated from their electromagnetically measured spin-down rates. These pulsars include the millisecond pulsars J0437−4715 and J0711−6830, which have spin-down ratios of 0.87 and 0.57, respectively. For nine pulsars, their spin-down limits have been surpassed for the first time. For the Crab and Vela pulsars, our limits are factors of ∼100 and ∼20 more constraining than their spin-down limits, respectively. For the dual-harmonic searches, new limits are placed on the strain amplitudes C 21 and C 22. For 23 pulsars, we also present limits on the emission amplitude assuming dipole radiation as predicted by Brans-Dicke theory.
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“Search of the early O3 LIGO data for continuous gravitational waves from the Cassiopeia A and Vela Jr. supernova remnants”, Physical Review D (2022).
R. Abbott, T. D. Abbott, F. Acernese, K. Ackley, and C. Adams, et al.Abstract
We present directed searches for continuous gravitational waves from the neutron stars in the Cassiopeia A (Cas A) and Vela Jr. supernova remnants. We carry out the searches in the LIGO detector data from the first six months of the third Advanced LIGO and Virgo observing run using the weave semicoherent method, which sums matched-filter detection-statistic values over many time segments spanning the observation period. No gravitational wave signal is detected in the search band of 20–976 Hz for assumed source ages greater than 300 years for Cas A and greater than 700 years for Vela Jr. Estimates from simulated continuous wave signals indicate we achieve the most sensitive results to date across the explored parameter space volume, probing to strain magnitudes as low as ∼6.3 × 10⁻²⁶ for Cas A and ∼5.6 × 10⁻²⁶ for Vela Jr. at frequencies near 166 Hz at 95% efficiency.
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“Search for Subsolar-Mass Binaries in the First Half of Advanced LIGO's and Advanced Virgo's Third Observing Run”, Physical Review Letters (2022).
R. Abbott, T. D. Abbott, F. Acernese, K. Ackley, and C. Adams, et al.Abstract
We report on a search for compact binary coalescences where at least one binary component has a mass between 0.2 M_⊙ and 1.0 M_⊙ in Advanced LIGO and Advanced Virgo data collected between 1 April 2019 1500 UTC and 1 October 2019 1500 UTC. We extend our previous analyses in two main ways: we include data from the Virgo detector and we allow for more unequal mass systems, with mass ratio q ≥ 0.1. We do not report any gravitational-wave candidates. The most significant trigger has a false alarm rate of 0.14 yr⁻¹. This implies an upper limit on the merger rate of subsolar binaries in the range [220 − 24200] Gpc⁻³ yr⁻¹, depending on the chirp mass of the binary. We use this upper limit to derive astrophysical constraints on two phenomenological models that could produce subsolar-mass compact objects. One is an isotropic distribution of equal-mass primordial black holes. Using this model, we find that the fraction of dark matter in primordial black holes in the mass range 0.2 M_⊙ < m_(PBH) < 1.0 M_⊙ is f_(PBH) ≡ Ω_(PBH)/Ω_(DM) ≲ 6%. This improves existing constraints on primordial black hole abundance by a factor of ∼3. The other is a dissipative dark matter model, in which fermionic dark matter can collapse and form black holes. The upper limit on the fraction of dark matter black holes depends on the minimum mass of the black holes that can be formed: the most constraining result is obtained at M_(min) = 1 M_⊙, where f_(DBH) ≡ Ω_(DBH)/Ω_(DM) ≲ 0.003%. These are the first constraints placed on dissipative dark models by subsolar-mass analyses.
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“Search for intermediate-mass black hole binaries in the third observing run of Advanced LIGO and Advanced Virgo”, Astronomy and Astrophysics (2022).
R. Abbott, T. D. Abbott, F. Acernese, K. Ackley, and C. Adams, et al.Abstract
Intermediate-mass black holes (IMBHs) span the approximate mass range 100−10⁵ M⊙, between black holes (BHs) that formed by stellar collapse and the supermassive BHs at the centers of galaxies. Mergers of IMBH binaries are the most energetic gravitational-wave sources accessible by the terrestrial detector network. Searches of the first two observing runs of Advanced LIGO and Advanced Virgo did not yield any significant IMBH binary signals. In the third observing run (O3), the increased network sensitivity enabled the detection of GW190521, a signal consistent with a binary merger of mass ∼150 M⊙ providing direct evidence of IMBH formation. Here, we report on a dedicated search of O3 data for further IMBH binary mergers, combining both modeled (matched filter) and model-independent search methods. We find some marginal candidates, but none are sufficiently significant to indicate detection of further IMBH mergers. We quantify the sensitivity of the individual search methods and of the combined search using a suite of IMBH binary signals obtained via numerical relativity, including the effects of spins misaligned with the binary orbital axis, and present the resulting upper limits on astrophysical merger rates. Our most stringent limit is for equal mass and aligned spin BH binary of total mass 200 M⊙ and effective aligned spin 0.8 at 0.056 Gpc⁻³ yr⁻¹ (90% confidence), a factor of 3.5 more constraining than previous LIGO-Virgo limits. We also update the estimated rate of mergers similar to GW190521 to 0.08 Gpc⁻³ yr⁻¹.
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“Search for gravitational waves from Scorpius X-1 with a hidden Markov model in O3 LIGO data”, Physical Review D (2022).
R. Abbott, H. Abe, F. Acernese, K. Ackley, and N. Adhikari, et al.Abstract
Results are presented for a semicoherent search for continuous gravitational waves from the low-mass x-ray binary Scorpius X-1, using a hidden Markov model (HMM) to allow for spin wandering. This search improves on previous HMM-based searches of Laser Interferometer Gravitational-Wave Observatory data by including the orbital period in the search template grid, and by analyzing data from the latest (third) observing run. In the frequency range searched, from 60 to 500 Hz, we find no evidence of gravitational radiation. This is the most sensitive search for Scorpius X-1 using a HMM to date. For the most sensitive subband, starting at 256.06 Hz, we report an upper limit on gravitational wave strain (at 95% confidence) of h^(95%)_0 = 6.16 × 10⁻²⁶, assuming the orbital inclination angle takes its electromagnetically restricted value ι = 44°. The upper limits on gravitational wave strain reported here are on average a factor of ∼ 3 lower than in the second observing run HMM search. This is the first Scorpius X-1 HMM search with upper limits that reach below the indirect torque-balance limit for certain subbands, assuming ι = 44°.
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“Search for Gravitational Waves Associated with Gamma-Ray Bursts Detected by Fermi and Swift during the LIGO–Virgo Run O3b”, Astrophysical Journal (2022).
R. Abbott, T. D. Abbott, F. Acernese, K. Ackley, and C. Adams, et al.Abstract
We search for gravitational-wave signals associated with gamma-ray bursts (GRBs) detected by the Fermi and Swift satellites during the second half of the third observing run of Advanced LIGO and Advanced Virgo (2019 November 1 15:00 UTC–2020 March 27 17:00 UTC). We conduct two independent searches: a generic gravitational-wave transients search to analyze 86 GRBs and an analysis to target binary mergers with at least one neutron star as short GRB progenitors for 17 events. We find no significant evidence for gravitational-wave signals associated with any of these GRBs. A weighted binomial test of the combined results finds no evidence for subthreshold gravitational-wave signals associated with this GRB ensemble either. We use several source types and signal morphologies during the searches, resulting in lower bounds on the estimated distance to each GRB. Finally, we constrain the population of low-luminosity short GRBs using results from the first to the third observing runs of Advanced LIGO and Advanced Virgo. The resulting population is in accordance with the local binary neutron star merger rate.
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“Search for continuous gravitational waves from 20 accreting millisecond x-ray pulsars in O3 LIGO data”, Physical Review D (2022).
R. Abbott, T. D. Abbott, F. Acernese, K. Ackley, and C. Adams, et al.Abstract
Results are presented of searches for continuous gravitational waves from 20 accreting millisecond x-ray pulsars with accurately measured spin frequencies and orbital parameters, using data from the third observing run of the Advanced LIGO and Advanced Virgo detectors. The search algorithm uses a hidden Markov model, where the transition probabilities allow the frequency to wander according to an unbiased random walk, while the J-statistic maximum-likelihood matched filter tracks the binary orbital phase. Three narrow subbands are searched for each target, centered on harmonics of the measured spin frequency. The search yields 16 candidates, consistent with a false alarm probability of 30% per subband and target searched. These candidates, along with one candidate from an additional target-of-opportunity search done for SAX J1808.4−3658, which was in outburst during one month of the observing run, cannot be confidently associated with a known noise source. Additional follow-up does not provide convincing evidence that any are a true astrophysical signal. When all candidates are assumed nonastrophysical, upper limits are set on the maximum wave strain detectable at 95% confidence, h^(95%)₀. The strictest constraint is h^(95%)₀ = 4.7×10⁻²⁶ from IGR J17062−6143. Constraints on the detectable wave strain from each target lead to constraints on neutron star ellipticity and r-mode amplitude, the strictest of which are ε^(95%) = 3.1×10⁻⁷ and α^(95%) = 1.8×10⁻⁵ respectively. This analysis is the most comprehensive and sensitive search of continuous gravitational waves from accreting millisecond x-ray pulsars to date.
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“Search for continuous gravitational wave emission from the Milky Way center in O3 LIGO-Virgo data”, Physical Review D (2022).
R. Abbott, H. Abe, F. Acernese, K. Ackley, and N. Adhikari, et al.Abstract
We present a directed search for continuous gravitational wave (CW) signals emitted by spinning neutron stars located in the inner parsecs of the Galactic Center (GC). Compelling evidence for the presence of a numerous population of neutron stars has been reported in the literature, turning this region into a very interesting place to look for CWs. In this search, data from the full O3 LIGO-Virgo run in the detector frequency band [10,2000] Hz have been used. No significant detection was found and 95% confidence level upper limits on the signal strain amplitude were computed, over the full search band, with the deepest limit of about 7.6 × 10⁻²⁶ at ≃ 142 Hz. These results are significantly more constraining than those reported in previous searches. We use these limits to put constraints on the fiducial neutron star ellipticity and r-mode amplitude. These limits can be also translated into constraints in the black hole mass–boson mass plane for a hypothetical population of boson clouds around spinning black holes located in the GC.
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“Scattering loss in precision metrology due to mirror roughness”, Journal of the Optical Society of America A (2022).
Yehonathan Drori, Johannes Eichholz, Tega Edo, Hiro Yamamoto, Yutaro Enomoto, Gautam Venugopalan, Koji Arai, and Rana X. AdhikariAbstract
Optical losses degrade the sensitivity of laser interferometric instruments. They reduce the number of signal photons and introduce technical noise associated with diffuse light. In quantum-enhanced metrology, they break the entanglement between correlated photons. Such decoherence is one of the primary obstacles in achieving high levels of quantum noise reduction in precision metrology. In this work, we compare direct measurements of cavity and mirror losses in the Caltech 40 m gravitational-wave detector prototype interferometer with numerical estimates obtained from semi-analytic intra-cavity wavefront simulations using mirror surface profile maps. We show a unified approach to estimating the total loss in optical cavities (such as the LIGO gravitational detectors) that will lead towards the engineering of systems with minimum decoherence for quantum-enhanced precision metrology.
Full text · DOI: 10.1364/josaa.455127
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“Optimizing gravitational-wave detector design for squeezed light”, Physical Review D (2022).
Jonathan W. Richardson, Swadha Pandey, Edita Bytyqi, Tega Edo, and Rana X. AdhikariAbstract
Achieving the quantum noise targets of third-generation detectors will require 10 dB of squeezed-light enhancement as well as megawatt laser power in the interferometer arms—both of which require unprecedented control of the internal optical losses. In this work, we present a novel optimization approach to gravitational-wave detector design aimed at maximizing the robustness to common, yet unavoidable, optical fabrication and installation errors, which have caused significant loss in Advanced LIGO. As a proof of concept, we employ these techniques to perform a two-part optimization of the LIGO A+ design. First, we optimize the arm cavities for reduced scattering loss in the presence of point absorbers, as currently limit the operating power of Advanced LIGO. Then, we optimize the signal recycling cavity for maximum squeezing performance, accounting for realistic errors in the positions and radii of curvature of the optics. Our findings suggest that these techniques can be leveraged to achieve substantially greater quantum noise performance in current and future gravitational-wave detectors.
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“Nonlinear Noise Cleaning in Gravitational-Wave Detectors With Convolutional Neural Networks”, Frontiers in Artificial Intelligence (2022).
Hang Yu and Rana X. AdhikariAbstract
Currently, the sub-60 Hz sensitivity of gravitational-wave (GW) detectors like Advanced LIGO (aLIGO) is limited by the control noises from auxiliary degrees of freedom which nonlinearly couple to the main GW readout. One promising way to tackle this challenge is to perform nonlinear noise mitigation using convolutional neural networks (CNNs), which we examine in detail in this study. In many cases, the noise coupling is bilinear and can be viewed as a few fast channels' outputs modulated by some slow channels. We show that we can utilize this knowledge of the physical system and adopt an explicit "slow×fast" structure in the design of the CNN to enhance its performance of noise subtraction. We then examine the requirements in the signal-to-noise ratio (SNR) in both the target channel (i.e., the main GW readout) and in the auxiliary sensors in order to reduce the noise by at least a factor of a few. In the case of limited SNR in the target channel, we further demonstrate that the CNN can still reach a good performance if we use curriculum learning techniques, which in reality can be achieved by combining data from quiet times and those from periods with active noise injections.
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“Narrowband Searches for Continuous and Long-duration Transient Gravitational Waves from Known Pulsars in the LIGO-Virgo Third Observing Run”, Astrophysical Journal (2022).
R. Abbott, T. D. Abbott, F. Acernese, K. Ackley, and C. Adams, et al.Abstract
Isolated neutron stars that are asymmetric with respect to their spin axis are possible sources of detectable continuous gravitational waves. This paper presents a fully coherent search for such signals from eighteen pulsars in data from LIGO and Virgo's third observing run (O3). For known pulsars, efficient and sensitive matched-filter searches can be carried out if one assumes the gravitational radiation is phase-locked to the electromagnetic emission. In the search presented here, we relax this assumption and allow both the frequency and the time derivative of the frequency of the gravitational waves to vary in a small range around those inferred from electromagnetic observations. We find no evidence for continuous gravitational waves, and set upper limits on the strain amplitude for each target. These limits are more constraining for seven of the targets than the spin-down limit defined by ascribing all rotational energy loss to gravitational radiation. In an additional search, we look in O3 data for long-duration (hours–months) transient gravitational waves in the aftermath of pulsar glitches for six targets with a total of nine glitches. We report two marginal outliers from this search, but find no clear evidence for such emission either. The resulting duration-dependent strain upper limits do not surpass indirect energy constraints for any of these targets.
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“Model-based Cross-correlation Search for Gravitational Waves from the Low-mass X-Ray Binary Scorpius X-1 in LIGO O3 Data”, Astrophysical Journal Letters (2022).
R. Abbott, H. Abe, F. Acernese, K. Ackley, and S. Adhicary, et al.Abstract
We present the results of a model-based search for continuous gravitational waves from the low-mass X-ray binary Scorpius X-1 using LIGO detector data from the third observing run of Advanced LIGO and Advanced Virgo. This is a semicoherent search that uses details of the signal model to coherently combine data separated by less than a specified coherence time, which can be adjusted to balance sensitivity with computing cost. The search covered a range of gravitational-wave frequencies from 25 to 1600 Hz, as well as ranges in orbital speed, frequency, and phase determined from observational constraints. No significant detection candidates were found, and upper limits were set as a function of frequency. The most stringent limits, between 100 and 200 Hz, correspond to an amplitude h₀ of about 10⁻²⁵ when marginalized isotropically over the unknown inclination angle of the neutron star's rotation axis, or less than 4 × 10⁻²⁶ assuming the optimal orientation. The sensitivity of this search is now probing amplitudes predicted by models of torque balance equilibrium. For the usual conservative model assuming accretion at the surface of the neutron star, our isotropically marginalized upper limits are close to the predicted amplitude from about 70 to 100 Hz; the limits assuming that the neutron star spin is aligned with the most likely orbital angular momentum are below the conservative torque balance predictions from 40 to 200 Hz. Assuming a broader range of accretion models, our direct limits on gravitational-wave amplitude delve into the relevant parameter space over a wide range of frequencies, to 500 Hz or more.
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“First joint observation by the underground gravitational-wave detector KAGRA with GEO 600”, Progress of Theoretical and Experimental Physics (2022).
R. Abbott, H. Abe, F. Acernese, K. Ackley, and N. Adhikari, et al.Abstract
We report the results of the first joint observation of the KAGRA detector with GEO 600. KAGRA is a cryogenic and underground gravitational-wave detector consisting of a laser interferometer with 3 km arms, located in Kamioka, Gifu, Japan. GEO 600 is a British–German laser interferometer with 600 m arms, located near Hannover, Germany. GEO 600 and KAGRA performed a joint observing run from April 7 to 20, 2020. We present the results of the joint analysis of the GEO–KAGRA data for transient gravitational-wave signals, including the coalescence of neutron-star binaries and generic unmodeled transients. We also perform dedicated searches for binary coalescence signals and generic transients associated with gamma-ray burst events observed during the joint run. No gravitational-wave events were identified. We evaluate the minimum detectable amplitude for various types of transient signals and the spacetime volume for which the network is sensitive to binary neutron-star coalescences. We also place lower limits on the distances to the gamma-ray bursts analyzed based on the non-detection of an associated gravitational-wave signal for several signal models, including binary coalescences. These analyses demonstrate the feasibility and utility of KAGRA as a member of the global gravitational-wave detector network.
Full text · DOI: 10.1093/ptep/ptac073
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“Exposing gravitational waves below the quantum sensing limit”, Physical Review D (2022).
Hang Yu, Denis Martynov, Rana X. Adhikari, and Yanbei ChenAbstract
The sensitivities of ground-based gravitational-wave (GW) detectors are limited by quantum shot noise at a few hundred hertz and above. Nonetheless, one can use a quantum-correlation technique proposed by Martynov et al. [Phys. Rev. A 95, 043831 (2017) to remove the expectation value of the shot noise, thereby exposing underlying classical signals in the cross spectrum formed by cross-correlating the two outputs in a GW interferometer's antisymmetric port. We explore here the prospects and analyze the sensitivity of using quantum correlation to detect astrophysical GW signals. Conceptually, this technique is similar to the correlation of two different GW detectors as it utilizes the fact that a GW signal will be correlated in the two outputs but the shot noise will be uncorrelated. Quantum correlation also has its unique advantages as it requires only a single interferometer to make a detection. Therefore, quantum correlation could increase the duty cycle, enhance the search efficiency, and enable the detection of highly polarized signals. In particular, we show that quantum correlation could be especially useful for detecting postmerger remnants of binary neutron stars with both short (< 1 s) and intermediate (∼10 - 10⁴ s) durations and setting upper limits on continuous emissions from unknown pulsars.
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“Constraints on dark photon dark matter using data from LIGO's and Virgo's third observing run”, Physical Review D (2022).
R. Abbott, T. D. Abbott, F. Acernese, K. Ackley, and C. Adams, et al.Abstract
We present a search for dark photon dark matter that could couple to gravitational-wave interferometers using data from Advanced LIGO and Virgo's third observing run. To perform this analysis, we use two methods, one based on cross-correlation of the strain channels in the two nearly aligned LIGO detectors, and one that looks for excess power in the strain channels of the LIGO and Virgo detectors. The excess power method optimizes the Fourier transform coherence time as a function of frequency, to account for the expected signal width due to Doppler modulations. We do not find any evidence of dark photon dark matter with a mass between m_A ∼ 10⁻¹⁴–10⁻¹¹ eV/c², which corresponds to frequencies between 10–2000 Hz, and therefore provide upper limits on the square of the minimum coupling of dark photons to baryons, i.e., U(1)_B dark matter. For the cross-correlation method, the best median constraint on the squared coupling is ∼1.31 × 10⁻⁴⁷ at m_A ∼ 4.2 × 10⁻¹³ eV/c²; for the other analysis, the best constraint is ∼2.4 × 10⁻⁴⁷ at m_A ∼ 5.7 × 10⁻¹³ eV/c². These limits improve upon those obtained in direct dark matter detection experiments by a factor of ∼100 for m_A ∼ [2–4] × 10⁻¹³ eV/c², and are, in absolute terms, the most stringent constraint so far in a large mass range m_A ∼ 2 × 10⁻¹³–8 × 10⁻¹² eV/c².
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“All-sky, all-frequency directional search for persistent gravitational waves from Advanced LIGO's and Advanced Virgo's first three observing runs”, Physical Review D (2022).
R. Abbott, T. D. Abbott, F. Acernese, K. Ackley, and C. Adams, et al.Abstract
We present the first results from an all-sky all-frequency (ASAF) search for an anisotropic stochastic gravitational-wave background using the data from the first three observing runs of the Advanced LIGO and Advanced Virgo detectors. Upper limit maps on broadband anisotropies of a persistent stochastic background were published for all observing runs of the LIGO-Virgo detectors. However, a broadband analysis is likely to miss narrowband signals as the signal-to-noise ratio of a narrowband signal can be significantly reduced when combined with detector output from other frequencies. Data folding and the computationally efficient analysis pipeline, PyStoch, enable us to perform the radiometer map-making at every frequency bin. We perform the search at 3072 HEALPix equal area pixels uniformly tiling the sky and in every frequency bin of width 1 / 32 Hz in the range 20–1726 Hz, except for bins that are likely to contain instrumental artefacts and hence are notched. We do not find any statistically significant evidence for the existence of narrowband gravitational-wave signals in the analyzed frequency bins. Therefore, we place 95% confidence upper limits on the gravitational-wave strain for each pixel-frequency pair, the limits are in the range (0.030 − 9.6) × 10⁻²⁴. In addition, we outline a method to identify candidate pixel-frequency pairs that could be followed up by a more sensitive (and potentially computationally expensive) search, e.g., a matched-filtering-based analysis, to look for fainter nearly monochromatic coherent signals. The ASAF analysis is inherently independent of models describing any spectral or spatial distribution of power. We demonstrate that the ASAF results can be appropriately combined over frequencies and sky directions to successfully recover the broadband directional and isotropic results.
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“All-sky search for gravitational wave emission from scalar boson clouds around spinning black holes in LIGO O3 data”, Physical Review D (2022).
R. Abbott, H. Abe, F. Acernese, K. Ackley, and N. Adhikari, et al.Abstract
This paper describes the first all-sky search for long-duration, quasimonochromatic gravitational-wave signals emitted by ultralight scalar boson clouds around spinning black holes using data from the third observing run of Advanced LIGO. We analyze the frequency range from 20 to 610 Hz, over a small frequency derivative range around zero, and use multiple frequency resolutions to be robust towards possible signal frequency wanderings. Outliers from this search are followed up using two different methods, one more suitable for nearly monochromatic signals, and the other more robust towards frequency fluctuations. We do not find any evidence for such signals and set upper limits on the signal strain amplitude, the most stringent being ≈10⁻²⁵ at around 130 Hz. We interpret these upper limits as both an "exclusion region" in the boson mass/black hole mass plane and the maximum detectable distance for a given boson mass, based on an assumption of the age of the black hole/boson cloud system.
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“All-sky search for continuous gravitational waves from isolated neutron stars using Advanced LIGO and Advanced Virgo O3 data”, (2022).
R. Abbott, H. Abe, F. Acernese, K. Ackley, and N. Adhikari, et al.Abstract
We present results of an all-sky search for continuous gravitational waves which can be produced by spinning neutron stars with an asymmetry around their rotation axis, using data from the third observing run of the Advanced LIGO and Advanced Virgo detectors. Four different analysis methods are used to search in a gravitational-wave frequency band from 10 to 2048 Hz and a first frequency derivative from −10⁻⁸ to 10⁻⁹ Hz/s. No statistically-significant periodic gravitational-wave signal is observed by any of the four searches. As a result, upper limits on the gravitational-wave strain amplitude h₀ are calculated. The best upper limits are obtained in the frequency range of 100 to 200 Hz and they are ∼1.1×10⁻²⁵ at 95% confidence-level. The minimum upper limit of 1.10×10⁻²⁵ is achieved at a frequency 111.5 Hz. We also place constraints on the rates and abundances of nearby planetary- and asteroid-mass primordial black holes that could give rise to continuous gravitational-wave signals.
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“All-sky search for continuous gravitational waves from isolated neutron stars using Advanced LIGO and Advanced Virgo O3 data”, Physical Review D (2022).
R. Abbott, H. Abe, F. Acernese, K. Ackley, and N. Adhikari, et al.Abstract
We present results of an all-sky search for continuous gravitational waves which can be produced by spinning neutron stars with an asymmetry around their rotation axis, using data from the third observing run of the Advanced LIGO and Advanced Virgo detectors. Four different analysis methods are used to search in a gravitational-wave frequency band from 10 to 2048 Hz and a first frequency derivative from −10⁻⁸ to 10⁻⁹ Hz/s. No statistically significant periodic gravitational-wave signal is observed by any of the four searches. As a result, upper limits on the gravitational-wave strain amplitude h₀ are calculated. The best upper limits are obtained in the frequency range of 100 to 200 Hz and they are ~ 1.1 × 10⁻²⁵ at 95% confidence level. The minimum upper limit of 1.10 × 10⁻²⁵ is achieved at a frequency 111.5 Hz. We also place constraints on the rates and abundances of nearby planetary- and asteroid-mass primordial black holes that could give rise to continuous gravitational-wave signals.
2021
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“Upper limits on the isotropic gravitational-wave background from Advanced LIGO and Advanced Virgo's third observing run”, Physical Review D (2021).
R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, and K. Ackley, et al.Abstract
We report results of a search for an isotropic gravitational-wave background (GWB) using data from Advanced LIGO's and Advanced Virgo's third observing run (O3) combined with upper limits from the earlier O1 and O2 runs. Unlike in previous observing runs in the advanced detector era, we include Virgo in the search for the GWB. The results of the search are consistent with uncorrelated noise, and therefore we place upper limits on the strength of the GWB. We find that the dimensionless energy density Ω_(GW) ≤ 5.8 × 10⁻⁹ at the 95% credible level for a flat (frequency-independent) GWB, using a prior which is uniform in the log of the strength of the GWB, with 99% of the sensitivity coming from the band 20–76.6 Hz; Ω_(GW)(f) ≤ 3.4 × 10⁻⁹ at 25 Hz for a power-law GWB with a spectral index of 2/3 (consistent with expectations for compact binary coalescences), in the band 20–90.6 Hz; and Ω_(GW)(f) ≤ 3.9 × 10⁻¹⁰ at 25 Hz for a spectral index of 3, in the band 20–291.6 Hz. These upper limits improve over our previous results by a factor of 6.0 for a flat GWB, 8.8 for a spectral index of 2/3, and 13.1 for a spectral index of 3. We also search for a GWB arising from scalar and vector modes, which are predicted by alternative theories of gravity; we do not find evidence of these, and place upper limits on the strength of GWBs with these polarizations. We demonstrate that there is no evidence of correlated noise of magnetic origin by performing a Bayesian analysis that allows for the presence of both a GWB and an effective magnetic background arising from geophysical Schumann resonances. We compare our upper limits to a fiducial model for the GWB from the merger of compact binaries, updating the model to use the most recent data-driven population inference from the systems detected during O3a. Finally, we combine our results with observations of individual mergers and show that, at design sensitivity, this joint approach may yield stronger constraints on the merger rate of binary black holes at z ≳ 2 than can be achieved with individually resolved mergers alone.
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“Tests of General Relativity with GWTC-3”, (2021).
R. Abbott, H. Abe, F. Acernese, K. Ackley, and N. Adhikari, et al.Abstract
The ever-increasing number of detections of gravitational waves (GWs) from compact binaries by the Advanced LIGO and Advanced Virgo detectors allows us to perform ever-more sensitive tests of general relativity (GR) in the dynamical and strong-field regime of gravity. We perform a suite of tests of GR using the compact binary signals observed during the second half of the third observing run of those detectors. We restrict our analysis to the 15 confident signals that have false alarm rates ≤10⁻³yr⁻¹. In addition to signals consistent with binary black hole (BH) mergers, the new events include GW200115_042309, a signal consistent with a neutron star--BH merger. We find the residual power, after subtracting the best fit waveform from the data for each event, to be consistent with the detector noise. Additionally, we find all the post-Newtonian deformation coefficients to be consistent with the predictions from GR, with an improvement by a factor of ~2 in the -1PN parameter. We also find that the spin-induced quadrupole moments of the binary BH constituents are consistent with those of Kerr BHs in GR. We find no evidence for dispersion of GWs, non-GR modes of polarization, or post-merger echoes in the events that were analyzed. We update the bound on the mass of the graviton, at 90% credibility, to m_g ≤ 1.27×10⁻²³eV/c². The final mass and final spin as inferred from the pre-merger and post-merger parts of the waveform are consistent with each other. The studies of the properties of the remnant BHs, including deviations of the quasi-normal mode frequencies and damping times, show consistency with the predictions of GR. In addition to considering signals individually, we also combine results from the catalog of GW signals to calculate more precise population constraints. We find no evidence in support of physics beyond GR.
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“Tests of general relativity with binary black holes from the second LIGO-Virgo gravitational-wave transient catalog”, Physical Review D (2021).
R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, and K. Ackley, et al.Abstract
Gravitational waves enable tests of general relativity in the highly dynamical and strong-field regime. Using events detected by LIGO-Virgo up to 1 October 2019, we evaluate the consistency of the data with predictions from the theory. We first establish that residuals from the best-fit waveform are consistent with detector noise, and that the low- and high-frequency parts of the signals are in agreement. We then consider parametrized modifications to the waveform by varying post-Newtonian and phenomenological coefficients, improving past constraints by factors of ∼2; we also find consistency with Kerr black holes when we specifically target signatures of the spin-induced quadrupole moment. Looking for gravitational-wave dispersion, we tighten constraints on Lorentz-violating coefficients by a factor of ∼2.6 and bound the mass of the graviton to m_g ≤ 1.76×10⁻²³ eV/c² with 90% credibility. We also analyze the properties of the merger remnants by measuring ringdown frequencies and damping times, constraining fractional deviations away from the Kerr frequency to δf₂₂₀ = 0.03^(+0.38)_(−0.35) for the fundamental quadrupolar mode, and δf₂₂₁ = 0.04^(+0.27)_(−0.32) for the first overtone; additionally, we find no evidence for postmerger echoes. Finally, we determine that our data are consistent with tensorial polarizations through a template-independent method. When possible, we assess the validity of general relativity based on collections of events analyzed jointly. We find no evidence for new physics beyond general relativity, for black hole mimickers, or for any unaccounted systematics.
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“Searches for Gravitational Waves from Known Pulsars at Two Harmonics in the Second and Third LIGO-Virgo Observing Runs”, (2021).
R. Abbott, H. Abe, F. Acernese, K. Ackley, and N. Adhikari, et al.Abstract
We present a targeted search for continuous gravitational waves (GWs) from 236 pulsars using data from the third observing run of LIGO and Virgo (O3) combined with data from the second observing run (O2). Searches were for emission from the l=m=2 mass quadrupole mode with a frequency at only twice the pulsar rotation frequency (single harmonic) and the l=2,m=1,2 modes with a frequency of both once and twice the rotation frequency (dual harmonic). No evidence of GWs was found so we present 95% credible upper limits on the strain amplitudes h0 for the single harmonic search along with limits on the pulsars' mass quadrupole moments Q₂₂ and ellipticities ε. Of the pulsars studied, 23 have strain amplitudes that are lower than the limits calculated from their electromagnetically measured spin-down rates. These pulsars include the millisecond pulsars J0437-4715 and J0711-6830 which have spin-down ratios of 0.87 and 0.57 respectively. For nine pulsars, their spin-down limits have been surpassed for the first time. For the Crab and Vela pulsars our limits are factors of ∼100 and ∼20 more constraining than their spin-down limits, respectively. For the dual harmonic searches, new limits are placed on the strain amplitudes C₂₁ and C₂₂. For 23 pulsars we also present limits on the emission amplitude assuming dipole radiation as predicted by Brans-Dicke theory.
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“Searches for Continuous Gravitational Waves from Young Supernova Remnants in the Early Third Observing Run of Advanced LIGO and Virgo”, Astrophysical Journal (2021).
R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, and K. Ackley, et al.Abstract
We present results of three wide-band directed searches for continuous gravitational waves from 15 young supernova remnants in the first half of the third Advanced LIGO and Virgo observing run. We use three search pipelines with distinct signal models and methods of identifying noise artifacts. Without ephemerides of these sources, the searches are conducted over a fRequency band spanning from 10 to 2 kHz. We find no evidence of continuous gravitational radiation from these sources. We set upper limits on the intrinsic signal strain at 95% confidence level in sample subbands, estimate the sensitivity in the full band, and derive the corresponding constraints on the fiducial neutron star ellipticity and r-mode amplitude. The best 95% confidence constraints placed on the signal strain are 7.7 × 10⁻²⁶ and 7.8 × 10⁻²⁶ near 200 Hz for the supernova remnants G39.2–0.3 and G65.7+1.2, respectively. The most stringent constraints on the ellipticity and r-mode amplitude reach ≲10⁻⁷ and ≲ 10⁻⁵, respectively, at frequencies above ∼400 Hz for the closest supernova remnant G266.2–1.2/Vela Jr.
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“Search for subsolar-mass binaries in the first half of Advanced LIGO and Virgo's third observing run”, (2021).
R. Abbott, T. D. Abbott, F. Acernese, K. Ackley, and C. Adams, et al.Abstract
We report on a search for compact binary coalescences where at least one binary component has a mass between 0.2 M_⊙ and 1.0 M_⊙ in Advanced LIGO and Advanced Virgo data collected between 1 April 2019 1500 UTC and 1 October 2019 1500 UTC. We extend previous analyses in two main ways: we include data from the Virgo detector and we allow for more unequal mass systems, with mass ratio q ≥ 0.1. We do not report any gravitational-wave candidates. The most significant trigger has a false alarm rate of 0.14 yr⁻¹. This implies an upper limit on the merger rate of subsolar binaries in the range [220−24200]Gpc⁻³yr⁻¹, depending on the chirp mass of the binary. We use this upper limit to derive astrophysical constraints on two phenomenological models that could produce subsolar-mass compact objects. One is an isotropic distribution of equal-mass primordial black holes. Using this model, we find that the fraction of dark matter in primordial black holes is fPBH≡ΩPBH/ΩDM≲6%. The other is a dissipative dark matter model, in which fermionic dark matter can collapse and form black holes. The upper limit on the fraction of dark matter black holes depends on the minimum mass of the black holes that can be formed: the most constraining result is obtained at M_(min) = 1 M_⊙, where f_(DBH) ≡ Ω_(PBH)/Ω_(DM) ≲ 0.003%. These are the tightest limits on spinning subsolar-mass binaries to date.
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“Search for Lensing Signatures in the Gravitational-Wave Observations from the First Half of LIGO–Virgo's Third Observing Run”, Astrophysical Journal (2021).
R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, and K. Ackley, et al.Abstract
We search for signatures of gravitational lensing in the gravitational-wave signals from compact binary coalescences detected by Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) and Advanced Virgo during O3a, the first half of their third observing run. We study: (1) the expected rate of lensing at current detector sensitivity and the implications of a non-observation of strong lensing or a stochastic gravitational-wave background on the merger-rate density at high redshift; (2) how the interpretation of individual high-mass events would change if they were found to be lensed; (3) the possibility of multiple images due to strong lensing by galaxies or galaxy clusters; and (4) possible wave-optics effects due to point-mass microlenses. Several pairs of signals in the multiple-image analysis show similar parameters and, in this sense, are nominally consistent with the strong lensing hypothesis. However, taking into account population priors, selection effects, and the prior odds against lensing, these events do not provide sufficient evidence for lensing. Overall, we find no compelling evidence for lensing in the observed gravitational-wave signals from any of these analyses.
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“Search for Gravitational Waves Associated with Gamma-Ray Bursts Detected by Fermi and Swift during the LIGO–Virgo Run O3a”, Astrophysical Journal (2021).
R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, and K. Ackley, et al.Abstract
We search for gravitational-wave transients associated with gamma-ray bursts (GRBs) detected by the Fermi and Swift satellites during the first part of the third observing run of Advanced LIGO and Advanced Virgo (2019 April 1 15:00 UTC–2019 October 1 15:00 UTC). A total of 105 GRBs were analyzed using a search for generic gravitational-wave transients; 32 GRBs were analyzed with a search that specifically targets neutron star binary mergers as short GRB progenitors. We find no significant evidence for gravitational-wave signals associated with the GRBs that we followed up, nor for a population of unidentified subthreshold signals. We consider several source types and signal morphologies, and report for these lower bounds on the distance to each GRB.
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“Search for anisotropic gravitational-wave backgrounds using data from Advanced LIGO and Advanced Virgo's first three observing runs”, Physical Review D (2021).
R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, and K. Ackley, et al.Abstract
We report results from searches for anisotropic stochastic gravitational-wave backgrounds using data from the first three observing runs of the Advanced LIGO and Advanced Virgo detectors. For the first t ime, we include Virgo data in our analysis and run our search with a new efficient pipeline called PyStoch on data folded over one sidereal day. We use gravitational-wave radiometry (broadband and narrow band) to produce sky maps of stochastic gravitational-wave backgrounds and to search for gravitational waves from point sources. A spherical harmonic decomposition method is employed to look for gravitational-wave emission from spatially-extended sources. Neither technique found evidence of gravitational-wave signals. Hence we derive 95% confidence-level upper limit sky maps on the gravitational-wave energy flux from broadband point sources, ranging from F_(α,Θ) < (0.013−7.6)×10⁻⁸ erg cm⁻² s⁻¹ Hz⁻¹, and on the (normalized) gravitational-wave energy density spectrum from extended sources, ranging from Ω_(α,Θ) < (0.57−9.3)×10⁻⁹ sr⁻¹, depending on direction (Θ) and spectral index (α). These limits improve upon previous limits by factors of 2.9–3.5. We also set 95% confidence level upper limits on the frequency-dependent strain amplitudes of quasimonochromatic gravitational waves coming from three interesting targets, Scorpius X-1, SN 1987A and the Galactic Center, with best upper limits range from h₀ < (1.7−2.1)×10⁻²⁵, a factor of ≥ 2.0 improvement compared to previous stochastic radiometer searches.
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“Reducing scattered light in LIGO's third observing run”, Classical and Quantum Gravity (2021).
S. Soni, C. Austin, A. Effler, R. M. S. Schofield, and G. González-Abad, et al.Abstract
Noise due to scattered light has been a frequent disturbance in the advanced LIGO gravitational wave detectors, hindering the detection of gravitational waves. The non stationary scatter noise caused by low frequency motion can be recognized as arches in the time-frequency plane of the gravitational wave channel. In this paper, we characterize the scattering noise for LIGO and Virgo's third observing run O3 from April, 2019 to March, 2020. We find at least two different populations of scattering noise and we investigate the multiple origins of one of them as well as its mitigation. We find that relative motion between two specific surfaces is strongly correlated with the presence of scattered light and we implement a technique to reduce this motion. We also present an algorithm using a witness channel to identify the times this noise can be present in the detector.
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“Population Properties of Compact Objects from the Second LIGO–Virgo Gravitational-Wave Transient Catalog”, Astrophysical Journal Letters (2021).
R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, and K. Ackley, et al.Abstract
We report on the population of 47 compact binary mergers detected with a false-alarm rate of < 1 yr⁻¹ in the second LIGO–Virgo Gravitational-Wave Transient Catalog. We observe several characteristics of the merging binary black hole (BBH) population not discernible until now. First, the primary mass spectrum contains structure beyond a power law with a sharp high-mass cutoff; it is more consistent with a broken power law with a break at 39.7^(+20.3)_(-9.1) M⊙ or a power law with a Gaussian feature peaking at 33.1^(+4.0)_(-5.6) M⊙ (90% credible interval). While the primary mass distribution must extend to ~65 M⊙ or beyond, only 2.9^(+3.5)_(-1.7)% of systems have primary masses greater than 45 M⊙. Second, we find that a fraction of BBH systems have component spins misaligned with the orbital angular momentum, giving rise to precession of the orbital plane. Moreover, 12%–44% of BBH systems have spins tilted by more than 90°, giving rise to a negative effective inspiral spin parameter, χ_(eff). Under the assumption that such systems can only be formed by dynamical interactions, we infer that between 25% and 93% of BBHs with nonvanishing |χ_(eff)| > 0.01 are dynamically assembled. Third, we estimate merger rates, finding R_(BBH) = 23.9^(+14.3)_(-8.6) Gpc⁻³yr⁻¹ for BBHs and R_(BNS) = 320^(+490)_(-240) Gpc⁻³yr⁻¹ for binary neutron stars. We find that the BBH rate likely increases with redshift (85% credibility) but not faster than the star formation rate (86% credibility). Additionally, we examine recent exceptional events in the context of our population models, finding that the asymmetric masses of GW190412 and the high component masses of GW190521 are consistent with our models, but the low secondary mass of GW190814 makes it an outlier.
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“Point absorbers in Advanced LIGO”, Applied Optics (2021).
Aidan F. Brooks, Gabriele Vajente, Hiro Yamamoto, Rich Abbott, and Carl Adams, et al.Abstract
Small, highly absorbing points are randomly present on the surfaces of the main interferometer optics in Advanced LIGO. The resulting nanometer scale thermo-elastic deformations and substrate lenses from these micron-scale absorbers significantly reduce the sensitivity of the interferometer directly though a reduction in the power-recycling gain and indirect interactions with the feedback control system. We review the expected surface deformation from point absorbers and provide a pedagogical description of the impact on power buildup in second generation gravitational wave detectors (dual-recycled Fabry–Perot Michelson interferometers). This analysis predicts that the power-dependent reduction in interferometer performance will significantly degrade maximum stored power by up to 50% and, hence, limit GW sensitivity, but it suggests system wide corrections that can be implemented in current and future GW detectors. This is particularly pressing given that future GW detectors call for an order of magnitude more stored power than currently used in Advanced LIGO in Observing Run 3. We briefly review strategies to mitigate the effects of point absorbers in current and future GW wave detectors to maximize the success of these enterprises.
Full text · DOI: 10.1364/ao.419689
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“Point Absorber Limits to Future Gravitational-Wave Detectors”, Physical Review Letters (2021).
Wenxuan Jia, Hiroaki Yamamoto, Kevin Kuns, Anamaria Effler, and Matthew Evans, et al.Abstract
High-quality optical resonant cavities require low optical loss, typically on the scale of parts per million. However, unintended micron-scale contaminants on the resonator mirrors that absorb the light circulating in the cavity can deform the surface thermoelastically and thus increase losses by scattering light out of the resonant mode. The point absorber effect is a limiting factor in some high-power cavity experiments, for example, the Advanced LIGO gravitational-wave detector. In this Letter, we present a general approach to the point absorber effect from first principles and simulate its contribution to the increased scattering. The achievable circulating power in current and future gravitational-wave detectors is calculated statistically given different point absorber configurations. Our formulation is further confirmed experimentally in comparison with the scattered power in the arm cavity of Advanced LIGO measured by in situ photodiodes. The understanding presented here provides an important tool in the global effort to design future gravitational-wave detectors that support high optical power and thus reduce quantum noise.
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“Open data from the first and second observing runs of Advanced LIGO and Advanced Virgo”, SoftwareX (2021).
R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, and K. Ackley, et al.Abstract
Advanced LIGO and Advanced Virgo are monitoring the sky and collecting gravitational-wave strain data with sufficient sensitivity to detect signals routinely. In this paper we describe the data recorded by these instruments during their first and second observing runs. The main data products are gravitational-wave strain time series sampled at 16384 Hz. The datasets that include this strain measurement can be freely accessed through the Gravitational Wave Open Science Center at http://gw-openscience.org, together with data-quality information essential for the analysis of LIGO and Virgo data, documentation, tutorials, and supporting software.
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“Observation of Gravitational Waves from Two Neutron Star–Black Hole Coalescences”, Astrophysical Journal Letters (2021).
R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, and K. Ackley, et al.Abstract
We report the observation of gravitational waves from two compact binary coalescences in LIGO's and Virgo's third observing run with properties consistent with neutron star–black hole (NSBH) binaries. The two events are named G_W200105_162426 and GW200115_042309, abbreviated as GW200105 and GW200115; the first was observed by LIGO Livingston and Virgo and the second by all three LIGO–Virgo detectors. The source of GW200105 has component masses 8.9^(+1.2)_(-1.5) and 1.9^(+0.3)_(-0.2) M_⊙, whereas the source of GW200115 has component masses 5.7^(+1.8)_(-2.1) and 1.5^(+0.7)_(-0.3) M_⊙ (all measurements quoted at the 90% credible level). The probability that the secondary's mass is below the maximal mass of a neutron star is 89%–96% and 87%–98%, respectively, for GW200105 and GW200115, with the ranges arising from different astrophysical assumptions. The source luminosity distances are 280⁺¹¹⁰₋₁₁₀ and 300⁺¹⁵⁰₋₁₀₀ Mpc, respectively. The magnitude of the primary spin of GW200105 is less than 0.23 at the 90% credible level, and its orientation is unconstrained. For GW200115, the primary spin has a negative spin projection onto the orbital angular momentum at 88% probability. We are unable to constrain the spin or tidal deformation of the secondary component for either event. We infer an NSBH merger rate density of 45⁺⁷⁵₋₃₃ Gpc⁻³ yr⁻¹ when assuming that GW200105 and GW200115 are representative of the NSBH population or 130⁺¹¹²₋₆₉ Gpc⁻³ yr⁻¹ under the assumption of a broader distribution of component masses.
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“LIGO's quantum response to squeezed states”, Physical Review D (2021).
L. McCuller, S. E. Dwyer, A. C. Green, Haocun Yu, and K. Kuns, et al.Abstract
Gravitational wave interferometers achieve their profound sensitivity by combining a Michelson interferometer with optical cavities, suspended masses, and now, squeezed quantum states of light. These states modify the measurement process of the LIGO, VIRGO and GEO600 interferometers to reduce the quantum noise that masks astrophysical signals; thus, improvements to squeezing are essential to further expand our gravitational view of the Universe. Further reducing quantum noise will require both lowering decoherence from losses as well more sophisticated manipulations to counter the quantum back-action from radiation pressure. Both tasks require fully understanding the physical interactions between squeezed light and the many components of km-scale interferometers. To this end, data from both LIGO observatories in observing run three are expressed using frequency-dependent metrics to analyze each detector's quantum response to squeezed states. The response metrics are derived and used to concisely describe physical mechanisms behind squeezing's simultaneous interaction with transverse-mode selective optical cavities and the quantum radiation pressure noise of suspended mirrors. These metrics and related analysis are broadly applicable for cavity-enhanced optomechanics experiments that incorporate external squeezing, and—for the first time—give physical descriptions of every feature so far observed in the quantum noise of the LIGO detectors.
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“LIGO detector characterization in the second and third observing runs”, Classical and Quantum Gravity (2021).
D. Davis, J. S. Areeda, B. K. Berger, R. Bruntz, and A. Effler, et al.Abstract
The characterization of the Advanced LIGO detectors in the second and third observing runs has increased the sensitivity of the instruments, allowing for a higher number of detectable gravitational-wave signals, and provided confirmation of all observed gravitational-wave events. In this work, we present the methods used to characterize the LIGO detectors and curate the publicly available datasets, including the LIGO strain data and data quality products. We describe the essential role of these datasets in LIGO–Virgo Collaboration analyses of gravitational-waves from both transient and persistent sources and include details on the provenance of these datasets in order to support analyses of LIGO data by the broader community. Finally, we explain anticipated changes in the role of detector characterization and current efforts to prepare for the high rate of gravitational-wave alerts and events in future observing runs.
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“GWTC-3: Compact Binary Coalescences Observed by LIGO and Virgo During the Second Part of the Third Observing Run”, (2021).
R. Abbott, T. D. Abbott, F. Acernese, K. Ackley, and C. Adams, et al.Abstract
The third Gravitational-wave Transient Catalog (GWTC-3) describes signals detected with Advanced LIGO and Advanced Virgo up to the end of their third observing run. Updating the previous GWTC-2.1, we present candidate gravitational waves from compact binary coalescences during the second half of the third observing run (O3b) between 1 November 2019, 15:00 UTC and 27 March 2020, 17:00 UTC. There are 35 compact binary coalescence candidates identified by at least one of our search algorithms with a probability of astrophysical origin p_(astro) > 0.5. Of these, 18 were previously reported as low-latency public alerts, and 17 are reported here for the first time. Based upon estimates for the component masses, our O3b candidates with p_(astro) > 0.5 are consistent with gravitational-wave signals from binary black holes or neutron star-black hole binaries, and we identify none from binary neutron stars. However, from the gravitational-wave data alone, we are not able to measure matter effects that distinguish whether the binary components are neutron stars or black holes. The range of inferred component masses is similar to that found with previous catalogs, but the O3b candidates include the first confident observations of neutron star-black hole binaries. Including the 35 candidates from O3b in addition to those from GWTC-2.1, GWTC-3 contains 90 candidates found by our analysis with p_(astro) > 0.5 across the first three observing runs. These observations of compact binary coalescences present an unprecedented view of the properties of black holes and neutron stars.
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“GWTC-2: Compact Binary Coalescences Observed by LIGO and Virgo during the First Half of the Third Observing Run”, Physical Review X (2021).
R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, and K. Ackley, et al.Abstract
We report on gravitational-wave discoveries from compact binary coalescences detected by Advanced LIGO and Advanced Virgo in the first half of the third observing run (O3a) between 1 April 2019 15∶00 UTC and 1 October 2019 15∶00 UTC. By imposing a false-alarm-rate threshold of two per year in each of the four search pipelines that constitute our search, we present 39 candidate gravitational-wave events. At this threshold, we expect a contamination fraction of less than 10%. Of these, 26 candidate events were reported previously in near-real time through gamma-ray coordinates network notices and circulars; 13 are reported here for the first time. The catalog contains events whose sources are black hole binary mergers up to a redshift of approximately 0.8, as well as events whose components cannot be unambiguously identified as black holes or neutron stars. For the latter group, we are unable to determine the nature based on estimates of the component masses and spins from gravitational-wave data alone. The range of candidate event masses which are unambiguously identified as binary black holes (both objects ≥3 M⊙) is increased compared to GWTC-1, with total masses from approximately 14 M⊙ for GW190924_021846 to approximately 150 M⊙ for GW190521. For the first time, this catalog includes binary systems with significantly asymmetric mass ratios, which had not been observed in data taken before April 2019. We also find that 11 of the 39 events detected since April 2019 have positive effective inspiral spins under our default prior (at 90% credibility), while none exhibit negative effective inspiral spin. Given the increased sensitivity of Advanced LIGO and Advanced Virgo, the detection of 39 candidate events in approximately 26 weeks of data (approximately 1.5 per week) is consistent with GWTC-1.
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“GWTC-2.1: Deep Extended Catalog of Compact Binary Coalescences Observed by LIGO and Virgo During the First Half of the Third Observing Run”, (2021).
R. Abbott, T. D. Abbott, F. Acernese, K. Ackley, and C. Adams, et al.Abstract
The second gravitational-wave transient catalog, GWTC-2, reported on 39 compact binary coalescences observed by the Advanced LIGO and Advanced Virgo detectors between 1 April 2019 15:00 UTC and 1 October 2019 15:00 UTC. Here, we present GWTC-2.1, which reports on a deeper list of candidate events observed over the same period. We analyze the final version of the strain data over this period, which is now publicly released. We employ three matched-filter search pipelines for candidate identification, and estimate the probability of astrophysical origin for each candidate event. While GWTC-2 used a false alarm rate threshold of 2 per year, we include in GWTC-2.1, 1201 candidates that pass a false alarm rate threshold of 2 per day. We calculate the source properties of a subset of 44 high-significance candidates that have a probability of astrophysical origin greater than 0.5, using the default priors. Of these candidates, 36 have been reported in GWTC-2. If the 8 additional high-significance candidates presented here are astrophysical, the mass range of candidate events that are unambiguously identified as binary black holes (both objects ≥ 3 M_⊙) is increased compared to GWTC-2, with total masses from ∼14 M_⊙ for GW190924_021846 to ∼184 M_⊙ for GW190426_190642. The primary components of two new candidate events (GW190403_051519 and GW190426_190642) fall in the mass gap predicted by pair-instability supernova theory. We also expand the population of binaries with significantly asymmetric mass ratios reported in GWTC-2 by an additional two events (q < 0.61 and q < 0.62 at 90% credibility for GW190403_051519 and GW190917_114630 respectively), and find that 2 of the 8 new events have effective inspiral spins χ_(eff) > 0 (at 90% credibility), while no binary is consistent with χ_(eff) < 0 at the same significance.
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“Gravitational-wave physics with Cosmic Explorer: Limits to low-frequency sensitivity”, Physical Review D (2021).
Evan D. Hall, Kevin Kuns, Joshua R. Smith, Yuntao Bai, Christopher Wipf, Sebastien Biscans, Rana X. Adhikari, Koji Arai, Stefan Ballmer, Lisa Barsotti, Yanbei Chen, Matthew Evans, Peter Fritschel, Jan Harms, Brittany Kamai, Jameson Graef Rollins, David Shoemaker, Bram J. J. Slagmolen, Rainer Weiss, and Hiro YamamotoAbstract
Cosmic Explorer is a next-generation ground-based gravitational-wave observatory concept, envisioned to begin operation in the 2030s and expected to be capable of observing binary neutron star and black hole mergers back to the time of the first stars. Cosmic Explorer's sensitive band will extend below 10 Hz, where the design is predominantly limited by geophysical, thermal, and quantum noises. In this work, thermal, seismic, gravity-gradient, quantum, residual gas, scattered-light, and servo-control noises are analyzed in order to motivate facility and vacuum system design requirements, potential test mass suspensions, Newtonian noise reduction strategies, improved inertial sensors, and cryogenic control requirements. Our analysis shows that, with improved technologies, Cosmic Explorer can deliver a strain sensitivity better than 10⁻²³ Hz^(−1/2) down to 5 Hz. Our work refines and extends previous analysis of the Cosmic Explorer concept and outlines the key research areas needed to make this observatory a reality.
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“Environmental noise in advanced LIGO detectors”, Classical and Quantum Gravity (2021).
P. Nguyen, R. M. S. Schofield, A. Effler, C. Austin, and V. Adya, et al.Abstract
The sensitivity of the advanced LIGO detectors to gravitational waves can be affected by environmental disturbances external to the detectors themselves. Since the transition from the former initial LIGO phase, many improvements have been made to the equipment and techniques used to investigate these environmental effects. These methods have aided in tracking down and mitigating noise sources throughout the first three observing runs of the advanced detector era, keeping the ambient contribution of environmental noise below the background noise levels of the detectors. In this paper we describe the methods used and how they have led to the mitigation of noise sources, the role that environmental monitoring has played in the validation of gravitational wave events, and plans for future observing runs.
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“Early warning of coalescing neutron-star and neutron-star-black-hole binaries from the nonstationary noise background using neural networks”, Physical Review D (2021).
Hang Yu, Rana X. Adhikari, Ryan Magee, Surabhi Sachdev, and Yanbei ChenAbstract
The success of the multimessenger astronomy relies on gravitational-wave observatories like LIGO and Virgo to provide prompt warning of merger events involving neutron stars (including both binary neutron stars and neutron-star-black-hole binaries), which further depends critically on the low-frequency sensitivity of LIGO as a typical binary neutron star stays in this band for minutes. However, the current sub-60 Hz sensitivity of LIGO has not yet reached its design target and the excess noise can be more than an order of magnitude below 20 Hz. It is limited by nonlinearly coupled noises from auxiliary control loops which are also nonstationary, posing challenges to realistic early warning pipelines. Nevertheless, machine-learning-based neural networks provide ways to simultaneously improve the low-frequency sensitivity and mitigate its nonstationarity, and detect the real-time gravitational-wave signal with a very short computational time. We propose to achieve this by inputting both the main gravitational-wave readout and key auxiliary witnesses to a compound neural network. Using simulated data with characteristic representing the real LIGO detectors, our machine-learning-based neural networks can reduce nonlinearly coupled noise by about a factor of 5 and allows a typical binary neutron star (neutron-star black hole) to be detected 100 s (10 s) before the merger at a distance of 40 Mpc (160 Mpc). If one can further reduce the noise to the fundamental limit, our neural networks can achieve detection out to a distance of 80 and 240 Mpc for binary neutron stars and neutron-star-black-hole binaries, respectively. It thus demonstrates that utilizing machine-learning-based neural networks is a promising direction for the timely detection of the coalescence of electromagnetically bright LIGO/Virgo sources.
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“Diving below the Spin-down Limit: Constraints on Gravitational Waves from the Energetic Young Pulsar PSR J0537-6910”, Astrophysical Journal Letters (2021).
R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, and K. Ackley, et al.Abstract
We present a search for quasi-monochromatic gravitational-wave signals from the young, energetic X-ray pulsar PSR J0537−6910 using data from the second and third observing runs of LIGO and Virgo. The search is enabled by a contemporaneous timing ephemeris obtained using Neutron star Interior Composition Explorer (NICER) data. The NICER ephemeris has also been extended through 2020 October and includes three new glitches. PSR J0537−6910 has the largest spin-down luminosity of any pulsar and exhibits fRequent and strong glitches. Analyses of its long-term and interglitch braking indices provide intriguing evidence that its spin-down energy budget may include gravitational-wave emission from a time-varying mass quadrupole moment. Its 62 Hz rotation frequency also puts its possible gravitational-wave emission in the most sensitive band of the LIGO/Virgo detectors. Motivated by these considerations, we search for gravitational-wave emission at both once and twice the rotation frequency from PSR J0537−6910. We find no signal, however, and report upper limits. Assuming a rigidly rotating triaxial star, our constraints reach below the gravitational-wave spin-down limit for this star for the first time by more than a factor of 2 and limit gravitational waves from the l = m = 2 mode to account for less than 14% of the spin-down energy budget. The fiducial equatorial ellipticity is constrained to less than about 3 ×10⁻⁵, which is the third best constraint for any young pulsar.
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“Constraints on Cosmic Strings Using Data from the Third Advanced LIGO–Virgo Observing Run”, Physical Review Letters (2021).
R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, and K. Ackley, et al.Abstract
We search for gravitational-wave signals produced by cosmic strings in the Advanced LIGO and Virgo full O3 dataset. Search results are presented for gravitational waves produced by cosmic string loop features such as cusps, kinks, and, for the first time, kink-kink collisions. A template-based search for short-duration transient signals does not yield a detection. We also use the stochastic gravitational-wave background energy density upper limits derived from the O3 data to constrain the cosmic string tension Gμ as a function of the number of kinks, or the number of cusps, for two cosmic string loop distribution models. Additionally, we develop and test a third model that interpolates between these two models. Our results improve upon the previous LIGO–Virgo constraints on Gμ by 1 to 2 orders of magnitude depending on the model that is tested. In particular, for the one-loop distribution model, we set the most competitive constraints to date: Gμ ≲ 4×10⁻¹⁵. In the case of cosmic strings formed at the end of inflation in the context of grand unified theories, these results challenge simple inflationary models.
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“Constraints from LIGO O3 Data on Gravitational-wave Emission Due to R-modes in the Glitching Pulsar PSR J0537–6910”, Astrophysical Journal (2021).
R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, and K. Ackley, et al.Abstract
We present a search for continuous gravitational-wave emission due to r-modes in the pulsar PSR J0537–6910 using data from the LIGO–Virgo Collaboration observing run O3. PSR J0537–6910 is a young energetic X-ray pulsar and is the most frequent glitcher known. The inter-glitch braking index of the pulsar suggests that gravitational-wave emission due to r-mode oscillations may play an important role in the spin evolution of this pulsar. Theoretical models confirm this possibility and predict emission at a level that can be probed by ground-based detectors. In order to explore this scenario, we search for r-mode emission in the epochs between glitches by using a contemporaneous timing ephemeris obtained from NICER data. We do not detect any signals in the theoretically expected band of 86–97 Hz, and report upper limits on the amplitude of the gravitational waves. Our results improve on previous amplitude upper limits from r-modes in J0537-6910 by a factor of up to 3 and place stringent constraints on theoretical models for r-mode-driven spin-down in PSR J0537–6910, especially for higher frequencies at which our results reach below the spin-down limit defined by energy conservation.
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“Approaching the motional ground state of a 10-kg object”, Science (2021).
Chris Whittle, Evan D. Hall, Sheila Dwyer, Nergis Mavalvala, and Vivishek Sudhir, et al.Abstract
The motion of a mechanical object, even a human-sized object, should be governed by the rules of quantum mechanics. Coaxing them into a quantum state is, however, difficult because the thermal environment masks any quantum signature of the object's motion. The thermal environment also masks the effects of proposed modifications of quantum mechanics at large mass scales. We prepared the center-of-mass motion of a 10-kilogram mechanical oscillator in a state with an average phonon occupation of 10.8. The reduction in temperature, from room temperature to 77 nanokelvin, is commensurate with an 11 orders-of-magnitude suppression of quantum back-action by feedback and a 13 orders-of-magnitude increase in the mass of an object prepared close to its motional ground state. Our approach will enable the possibility of probing gravity on massive quantum systems.
Full text · DOI: 10.1126/science.abh2634
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“All-sky, all-frequency directional search for persistent gravitational-waves from Advanced LIGO's and Advanced Virgo's first three observing runs”, (2021).
R. Abbott, T. D. Abbott, F. Acernese, K. Ackley, and C. Adams, et al.Abstract
We present the first results from an all-sky all-frequency (ASAF) search for an anisotropic stochastic gravitational-wave background using the data from the first three observing runs of the Advanced LIGO and Advanced Virgo detectors. Upper limit maps on broadband anisotropies of a persistent stochastic background were published for all observing runs of the LIGO-Virgo detectors. However, a broadband analysis is likely to miss narrowband signals as the signal-to-noise ratio of a narrowband signal can be significantly reduced when combined with detector output from other frequencies. Data folding and the computationally efficient analysis pipeline, PyStoch, enable us to perform the radiometer map-making at every frequency bin. We perform the search at 3072 HEALPix equal area pixels uniformly tiling the sky and in every frequency bin of width 1/32~Hz in the range 20−1726~Hz, except for bins that are likely to contain instrumental artefacts and hence are notched. We do not find any statistically significant evidence for the existence of narrowband gravitational-wave signals in the analyzed frequency bins. Therefore, we place 95% confidence upper limits on the gravitational-wave strain for each pixel-frequency pair, the limits are in the range (0.030−9.6) × 10⁻²⁴. In addition, we outline a method to identify candidate pixel-frequency pairs that could be followed up by a more sensitive (and potentially computationally expensive) search, e.g., a matched-filtering-based analysis, to look for fainter nearly monochromatic coherent signals. The ASAF analysis is inherently independent of models describing any spectral or spatial distribution of power. We demonstrate that the ASAF results can be appropriately combined over frequencies and sky directions to successfully recover the broadband directional and isotropic results.
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“All-sky search in early O3 LIGO data for continuous gravitational-wave signals from unknown neutron stars in binary systems”, Physical Review D (2021).
R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, and K. Ackley, et al.Abstract
Rapidly spinning neutron stars are promising sources of continuous gravitational waves. Detecting such a signal would allow probing of the physical properties of matter under extreme conditions. A significant fraction of the known pulsar population belongs to binary systems. Searching for unknown neutron stars in binary systems requires specialized algorithms to address unknown orbital frequency modulations. We present a search for continuous gravitational waves emitted by neutron stars in binary systems in early data from the third observing run of the Advanced LIGO and Advanced Virgo detectors using the semicoherent, GPU-accelerated, binaryskyhough pipeline. The search analyzes the most sensitive frequency band of the LIGO detectors, 50–300 Hz. Binary orbital parameters are split into four regions, comprising orbital periods of three to 45 days and projected semimajor axes of two to 40 light seconds. No detections are reported. We estimate the sensitivity of the search using simulated continuous wave signals, achieving the most sensitive results to date across the analyzed parameter space.
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“All-sky search for short gravitational-wave bursts in the third Advanced LIGO and Advanced Virgo run”, Physical Review D (2021).
R. Abbott, T. D. Abbott, F. Acernese, K. Ackley, and C. Adams, et al.Abstract
This paper presents the results of a search for generic short-duration gravitational-wave transients in data from the third observing run of Advanced LIGO and Advanced Virgo. Transients with durations of milliseconds to a few seconds in the 24–4096 Hz frequency band are targeted by the search, with no assumptions made regarding the incoming signal direction, polarization, or morphology. Gravitational waves from compact binary coalescences that have been identified by other targeted analyses are detected, but no statistically significant evidence for other gravitational wave bursts is found. Sensitivities to a variety of signals are presented. These include updated upper limits on the source rate density as a function of the characteristic frequency of the signal, which are roughly an order of magnitude better than previous upper limits. This search is sensitive to sources radiating as little as ∼10⁻¹⁰ M⊙c² in gravitational waves at ∼70 Hz from a distance of 10 kpc, with 50% detection efficiency at a false alarm rate of one per century. The sensitivity of this search to two plausible astrophysical sources is estimated: neutron star f modes, which may be excited by pulsar glitches, as well as selected core-collapse supernova models.
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“All-sky search for long-duration gravitational-wave bursts in the third Advanced LIGO and Advanced Virgo run”, Physical Review D (2021).
R. Abbott, T. D. Abbott, F. Acernese, K. Ackley, and C. Adams, et al.Abstract
After the detection of gravitational waves from compact binary coalescences, the search for transient gravitational-wave signals with less well-defined waveforms for which matched filtering is not well suited is one of the frontiers for gravitational-wave astronomy. Broadly classified into "short" ≲1 s and "long" ≳1 s duration signals, these signals are expected from a variety of astrophysical processes, including non-axisymmetric deformations in magnetars or eccentric binary black hole coalescences. In this work, we present a search for long-duration gravitational-wave transients from Advanced LIGO and Advanced Virgo's third observing run from April 2019 to March 2020. For this search, we use minimal assumptions for the sky location, event time, waveform morphology, and duration of the source. The search covers the range of 2–500 s in duration and a frequency band of 24–2048 Hz. We find no significant triggers within this parameter space; we report sensitivity limits on the signal strength of gravitational waves characterized by the root-sum-square amplitude h_(rss) as a function of waveform morphology. These h_(rss) limits improve upon the results from the second observing run by an average factor of 1.8.
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“All-sky search for continuous gravitational waves from isolated neutron stars in the early O3 LIGO data”, Physical Review D (2021).
R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, and K. Ackley, et al.Abstract
We report on an all-sky search for continuous gravitational waves in the frequency band 20–2000 Hz and with a frequency time derivative in the range of [−1.0, +0.1] × 10⁻⁸ Hz/s. Such a signal could be produced by a nearby, spinning and slightly nonaxisymmetric isolated neutron star in our Galaxy. This search uses the LIGO data from the first six months of Advanced LIGO's and Advanced Virgo's third observational run, O3. No periodic gravitational wave signals are observed, and 95% confidence-level (C.L.) frequentist upper limits are placed on their strengths. The lowest upper limits on worst-case (linearly polarized) strain amplitude h₀ are ∼1.7 × 10⁻²⁵ near 200 Hz. For a circularly polarized source (most favorable orientation), the lowest upper limits are ∼6.3 × 10⁻²⁶. These strict frequentist upper limits refer to all sky locations and the entire range of frequency derivative values. For a population-averaged ensemble of sky locations and stellar orientations, the lowest 95% C.L. upper limits on the strain amplitude are ∼1.4 × 10⁻²⁵. These upper limits improve upon our previously published all-sky results, with the greatest improvement (factor of ∼2) seen at higher frequencies, in part because quantum squeezing has dramatically improved the detector noise level relative to the second observational run, O2. These limits are the most constraining to date over most of the parameter space searched.
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“A Gravitational-wave Measurement of the Hubble Constant Following the Second Observing Run of Advanced LIGO and Virgo”, Astrophysical Journal (2021).
B. P. Abbott, R. Abbott, R. X. Adhikari, S. Anand, and A. Ananyeva, et al.Abstract
This paper presents the gravitational-wave measurement of the Hubble constant (H₀) using the detections from the first and second observing runs of the Advanced LIGO and Virgo detector network. The presence of the transient electromagnetic counterpart of the binary neutron star GW170817 led to the first standard-siren measurement of H₀. Here we additionally use binary black hole detections in conjunction with galaxy catalogs and report a joint measurement. Our updated measurement is H₀ = 69⁺¹⁶₋₈ km s⁻¹ Mpc⁻¹ (68.3% of the highest density posterior interval with a flat-in-log prior) which is an improvement by a factor of 1.04 (about 4%) over the GW170817-only value of 69⁺¹⁷₋₈ km s⁻¹ Mpc⁻¹. A significant additional contribution currently comes from GW170814, a loud and well-localized detection from a part of the sky thoroughly covered by the Dark Energy Survey. With numerous detections anticipated over the upcoming years, an exhaustive understanding of other systematic effects are also going to become increasingly important. These results establish the path to cosmology using gravitational-wave observations with and without transient electromagnetic counterparts.
2020
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“Silicon emissivity as a function of temperature”, International Journal of Heat and Mass Transfer (2020).
Marcio, Jr. Constancio, Rana X. Adhikari, Odylio D. Aguiar, Koji Arai, Aaron Markowitz, Marcos A. Okada, and Chris C. WipfAbstract
In this paper we present the temperature-dependent emissivity of a silicon sample, estimated from its cool-down curve in a constant low temperature environment ( ~ 82K). The emissivity value follow a linear dependency in the 120–260 K temperature range. This result is of great interest to the LIGO Voyager gravitational wave interferometer project since it would mean that no extra high thermal emissivity coating on the test masses would be required in order to cool them down to 123 K. The results presented here indicate that bulk silicon itself can have sufficient thermal emissivity in order to cool the 200 kg LIGO Voyager test masses only by radiation in a reasonable short amount of time (less than a week). However, it is still not clear if the natural emissivity of silicon will be sufficient to maintain the LIGO Voyager test masses at the desired temperature (123 K) while removing power absorbed by the test masses. With the present results, a black coating on the barrel surface of the test masses would be necessary if power in excess of 6 W is delivered. However, the agreement we found between the hemispherical emissivity obtained by a theory of semi-transparent Silicon and the obtained experimental results makes us believe that the LIGO Voyager test masses, because of their dimensions, will have effective emissivities around 0.7, which would be enough to remove about 8.6 W (7.5 W) for a shield at 60 K (80 K). This hypothesis may be confirmed in the near future with new measurements.
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“Sensitivity and performance of the Advanced LIGO detectors in the third observing run”, Physical Review D (2020).
A. Buikema, C. Cahillane, G. L. Mansell, C. D. Blair, and R. Abbott, et al.Abstract
On April 1st, 2019, the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO), joined by the Advanced Virgo detector, began the third observing run, a year-long dedicated search for gravitational radiation. The LIGO detectors have achieved a higher duty cycle and greater sensitivity to gravitational waves than ever before, with LIGO Hanford achieving angle-averaged sensitivity to binary neutron star coalescences to a distance of 111 Mpc, and LIGO Livingston to 134 Mpc with duty factors of 74.6% and 77.0% respectively. The improvement in sensitivity and stability is a result of several upgrades to the detectors, including doubled intracavity power, the addition of an in-vacuum optical parametric oscillator for squeezed-light injection, replacement of core optics and end reaction masses, and installation of acoustic mode dampers. This paper explores the purposes behind these upgrades, and explains to the best of our knowledge the noise currently limiting the sensitivity of each detector.
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“Quantum correlations between light and the kilogram-mass mirrors of LIGO”, Nature (2020).
Haocun Yu, L. McCuller, M. Tse, L. Barsotti, and N. Mavalvala, et al.Abstract
The measurement of minuscule forces and displacements with ever greater precision is inhibited by the Heisenberg uncertainty principle, which imposes a limit to the precision with which the position of an object can be measured continuously, known as the standard quantum limit. When light is used as the probe, the standard quantum limit arises from the balance between the uncertainties of the photon radiation pressure applied to the object and of the photon number in the photoelectric detection. The only way to surpass the standard quantum limit is by introducing correlations between the position/momentum uncertainty of the object and the photon number/phase uncertainty of the light that it reflects. Here we confirm experimentally the theoretical prediction that this type of quantum correlation is naturally produced in the Laser Interferometer Gravitational-wave Observatory (LIGO). We characterize and compare noise spectra taken without squeezing and with squeezed vacuum states injected at varying quadrature angles. After subtracting classical noise, our measurements show that the quantum mechanical uncertainties in the phases of the 200-kilowatt laser beams and in the positions of the 40-kilogram mirrors of the Advanced LIGO detectors yield a joint quantum uncertainty that is a factor of 1.4 (3 decibels) below the standard quantum limit. We anticipate that the use of quantum correlations will improve not only the observation of gravitational waves, but also more broadly future quantum noise-limited measurements.
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“Properties and Astrophysical Implications of the 150 M_⊙ Binary Black Hole Merger GW190521”, Astrophysical Journal Letters (2020).
R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, and K. Ackley, et al.Abstract
The gravitational-wave signal GW190521 is consistent with a binary black hole (BBH) merger source at redshift 0.8 with unusually high component masses, 85⁺²¹₋₁₄ M_⊙ and 66⁺¹⁷₋₁₈ M_⊙, compared to previously reported events, and shows mild evidence for spin-induced orbital precession. The primary falls in the mass gap predicted by (pulsational) pair-instability supernova theory, in the approximate range 65–120 M_⊙. The probability that at least one of the black holes in GW190521 is in that range is 99.0%. The final mass of the merger 142⁺²⁸₋₁₆ M_⊙) classifies it as an intermediate-mass black hole. Under the assumption of a quasi-circular BBH coalescence, we detail the physical properties of GW190521's source binary and its post-merger remnant, including component masses and spin vectors. Three different waveform models, as well as direct comparison to numerical solutions of general relativity, yield consistent estimates of these properties. Tests of strong-field general relativity targeting the merger-ringdown stages of the coalescence indicate consistency of the observed signal with theoretical predictions. We estimate the merger rate of similar systems to be 0.13_(-0.11)^(+0.30) Gpc⁻³ yr⁻¹. We discuss the astrophysical implications of GW190521 for stellar collapse and for the possible formation of black holes in the pair-instability mass gap through various channels: via (multiple) stellar coalescences, or via hierarchical mergers of lower-mass black holes in star clusters or in active galactic nuclei. We find it to be unlikely that GW190521 is a strongly lensed signal of a lower-mass black hole binary merger. We also discuss more exotic possible sources for GW190521, including a highly eccentric black hole binary, or a primordial black hole binary.
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“Phase-sensitive optomechanical amplifier for quantum noise reduction in laser interferometers”, Physical Review A (2020).
Yuntao Bai, Gautam Venugopalan, Kevin Kuns, Christopher Wipf, Aaron Markowitz, Andrew R. Wade, Yanbei Chen, and Rana X. AdhikariAbstract
The sensitivity of future gravitational wave interferometers is expected to be limited throughout the detection band by quantum vacuum fluctuations, which can be reduced by applying quantum optics techniques such as squeezed vacuum injection. However, decoherence caused by optical losses in the readout chain will severely limit the effectiveness of such schemes. It was proposed that effect of losses in the final stage of detection can be mitigated by a phase-sensitive amplifier placed in between the output port of the interferometer and the photodetector. In this paper we propose to implement such amplification using an optomechanical device, study some of its practical limitations, and discuss its applicability to next-generation gravitational-wave detectors.
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“Noise Reduction in Gravitational-wave Data via Deep Learning”, Physical Review Research (2020).
Rich Ormiston, Tri Nguyen, Michael Coughlin, Rana X. Adhikari, and Erik KatsavounidisAbstract
With the advent of gravitational wave astronomy, techniques to extend the reach of gravitational wave detectors are desired. In addition to the stellar-mass black hole and neutron star mergers already detected, many more are below the surface of the noise, available for detection if the noise is reduced enough. Our method (DeepClean) applies machine learning algorithms to gravitational wave detector data and data from on-site sensors monitoring the instrument to reduce the noise in the time-series due to instrumental artifacts and environmental contamination. This framework is generic enough to subtract linear, non-linear, and non-stationary coupling mechanisms. It may also provide handles in learning about the mechanisms which are not currently understood to be limiting detector sensitivities. The robustness of the noise reduction technique in its ability to efficiently remove noise with no unintended effects on gravitational-wave signals is also addressed through software signal injection and parameter estimation of the recovered signal. It is shown that the optimal SNR ratio of the injected signal is enhanced by ∼21.6% and the recovered parameters are consistent with the injected set. We present the performance of this algorithm on linear and non-linear noise sources and discuss its impact on astrophysical searches by gravitational wave detectors.
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“Measurement of mechanical losses in the carbon nanotube black coating of silicon wafers”, Classical and Quantum Gravity (2020).
L. G. Prokhorov, V. P. Mitrofanov, B. Kamai, A. Markowitz, Xiaoyue Ni, and R. X. AdhikariAbstract
The successful detection of gravitational waves from astrophysical sources carried out by the laser interferometric detectors LIGO and Virgo have stimulated scientists to develop a new generation of more sensitive gravitational wave detectors. In the proposed upgrade called LIGO Voyager, silicon test masses will be cooled to cryogenic temperatures. To provide heat removal from the test masses when they absorb the laser light one can increase their thermal emissivity using a special black coating. We have studied mechanical losses in a carbon nanotube black coating deposited on silicon wafers. The additional thermal noise associated with mechanical loss in this coating was calculated using a value of the product of the coating Young's modulus and the coating mechanical loss angle determined from the measurements. It was found that at temperatures of about 123 K, the additional thermal noise of the LIGO Voyager test mass caused by the carbon nanotube black coating deposited on its barrel is less than the noise associated with the Acktar Black coating and is 20 times less than the noise due to the optical high reflective (HR) coating of the test mass.
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“Improving the robustness of the advanced LIGO detectors to earthquakes”, Classical and Quantum Gravity (2020).
E. Schwartz, A. Pele, J. Warner, B. Lantz, and J. Betzwieser, et al.Abstract
Teleseismic, or distant, earthquakes regularly disrupt the operation of ground–based gravitational wave detectors such as Advanced LIGO. Here, we present EQ mode, a new global control scheme, consisting of an automated sequence of optimized control filters that reduces and coordinates the motion of the seismic isolation platforms during earthquakes. This, in turn, suppresses the differential motion of the interferometer arms with respect to one another, resulting in a reduction of DARM signal at frequencies below 100 mHz. Our method greatly improved the interferometers' capability to remain operational during earthquakes, with ground velocities up to 3.9 μm s⁻¹ rms in the beam direction, setting a new record for both detectors. This sets a milestone in seismic controls of the Advanced LIGO detectors' ability to manage high ground motion induced by earthquakes, opening a path for further robust operation in other extreme environmental conditions.
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“GW190814: Gravitational Waves from the Coalescence of a 23 Solar Mass Black Hole with a 2.6 Solar Mass Compact Object”, Astrophysical Journal Letters (2020).
R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, and K. Ackley, et al.Abstract
We report the observation of a compact binary coalescence involving a 22.2–24.3 M_⊙ black hole and a compact object with a mass of 2.50–2.67 M_⊙ (all measurements quoted at the 90% credible level). The gravitational-wave signal, GW190814, was observed during LIGO's and Virgo's third observing run on 2019 August 14 at 21:10:39 UTC and has a signal-to-noise ratio of 25 in the three-detector network. The source was localized to 18.5 deg² at a distance of 241_(-45)^(+41) Mpc; no electromagnetic counterpart has been confirmed to date. The source has the most unequal mass ratio yet measured with gravitational waves, 0.112_(-0.009)^(+0.008), and its secondary component is either the lightest black hole or the heaviest neutron star ever discovered in a double compact-object system. The dimensionless spin of the primary black hole is tightly constrained to ≤ 0.07. Tests of general relativity reveal no measurable deviations from the theory, and its prediction of higher-multipole emission is confirmed at high confidence. We estimate a merger rate density of 1–23 Gpc⁻³ yr⁻¹ for the new class of binary coalescence sources that GW190814 represents. Astrophysical models predict that binaries with mass ratios similar to this event can form through several channels, but are unlikely to have formed in globular clusters. However, the combination of mass ratio, component masses, and the inferred merger rate for this event challenges all current models of the formation and mass distribution of compact-object binaries.
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“GW190521: A Binary Black Hole Merger with a Total Mass of 150 M_⊙”, Physical Review Letters (2020).
R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, and K. Ackley, et al.Abstract
On May 21, 2019 at 03:02:29 UTC Advanced LIGO and Advanced Virgo observed a short duration gravitational-wave signal, GW190521, with a three-detector network signal-to-noise ratio of 14.7, and an estimated false-alarm rate of 1 in 4900 yr using a search sensitive to generic transients. If GW190521 is from a quasicircular binary inspiral, then the detected signal is consistent with the merger of two black holes with masses of 85⁺²¹₋₁₄ M_⊙ and 66⁺¹⁷₋₁₈ M_⊙ (90% credible intervals). We infer that the primary black hole mass lies within the gap produced by (pulsational) pair-instability supernova processes, with only a 0.32% probability of being below 65 M_⊙. We calculate the mass of the remnant to be 142⁺²⁸₋₁₆ M_⊙, which can be considered an intermediate mass black hole (IMBH). The luminosity distance of the source is 5.3^(+2.4)_(−2.6) Gpc, corresponding to a redshift of 0.82^(+0.28)_(−0.34). The inferred rate of mergers similar to GW190521 is 0.13^(+0.30)_(−0.11) Gpc⁻³ yr⁻¹.
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“GW190425: Observation of a Compact Binary Coalescence with Total Mass ~3.4 M⊙”, Astrophysical Journal Letters (2020).
B. P. Abbott, R. Abbott, R. X. Adhikari, S. Anand, and A. Ananyeva, et al.Abstract
On 2019 April 25, the LIGO Livingston detector observed a compact binary coalescence with signal-to-noise ratio 12.9. The Virgo detector was also taking data that did not contribute to detection due to a low signal-to-noise ratio, but were used for subsequent parameter estimation. The 90% credible intervals for the component masses range from 1.12 to 2.52 M⊙ (1.46 – 1.87 M⊙ if we restrict the dimensionless component spin magnitudes to be smaller than 0.05). These mass parameters are consistent with the individual binary components being neutron stars. However, both the source-frame chirp mass 1.44^(+0.02)_(-0.02) M⊙ and the total mass 3.4^(+0.3)_(-0.1) M⊙ of this system are significantly larger than those of any other known binary neutron star (BNS) system. The possibility that one or both binary components of the system are black holes cannot be ruled out from gravitational-wave data. We discuss possible origins of the system based on its inconsistency with the known Galactic BNS population. Under the assumption that the signal was produced by a BNS coalescence, the local rate of neutron star mergers is updated to 250–2810 Gpc⁻³ yr⁻¹.
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“GW190412: Observation of a Binary-Black-Hole Coalescence with Asymmetric Masses”, Physical Review D (2020).
R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, and K. Ackley, et al.Abstract
We report the observation of gravitational waves from a binary-black-hole coalescence during the first two weeks of LIGO's and Virgo's third observing run. The signal was recorded on April 12, 2019 at 05∶30∶44 UTC with a network signal-to-noise ratio of 19. The binary is different from observations during the first two observing runs most notably due to its asymmetric masses: a ∼30 M_⊙ black hole merged with a ∼8 M_⊙ black hole companion. The more massive black hole rotated with a dimensionless spin magnitude between 0.22 and 0.60 (90% probability). Asymmetric systems are predicted to emit gravitational waves with stronger contributions from higher multipoles, and indeed we find strong evidence for gravitational radiation beyond the leading quadrupolar order in the observed signal. A suite of tests performed on GW190412 indicates consistency with Einstein's general theory of relativity. While the mass ratio of this system differs from all previous detections, we show that it is consistent with the population model of stellar binary black holes inferred from the first two observing runs.
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“Gravitational-wave Constraints on the Equatorial Ellipticity of Millisecond Pulsars”, Astrophysical Journal Letters (2020).
R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, and K. Ackley, et al.Abstract
We present a search for continuous gravitational waves from five radio pulsars, comprising three recycled pulsars (PSR J0437−4715, PSR J0711−6830, and PSR J0737−3039A) and two young pulsars: the Crab pulsar (J0534+2200) and the Vela pulsar (J0835−4510). We use data from the third observing run of Advanced LIGO and Virgo combined with data from their first and second observing runs. For the first time, we are able to match (for PSR J0437−4715) or surpass (for PSR J0711−6830) the indirect limits on gravitational-wave emission from recycled pulsars inferred from their observed spin-downs, and constrain their equatorial ellipticities to be less than 10⁻⁸. For each of the five pulsars, we perform targeted searches that assume a tight coupling between the gravitational-wave and electromagnetic signal phase evolution. We also present constraints on PSR J0711−6830, the Crab pulsar, and the Vela pulsar from a search that relaxes this assumption, allowing the gravitational-wave signal to vary from the electromagnetic expectation within a narrow band of frequencies and frequency derivatives.
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“Astrophysics and cosmology with a decihertz gravitational-wave detector: TianGO”, Physical Review D (2020).
Kevin A. Kuns, Hang Yu, Yanbei Chen, and Rana X. AdhikariAbstract
We present the astrophysical science case for a space-based, decihertz gravitational-wave (GW) detector. We particularly highlight an ability to infer a source's sky location, both when combined with a network of ground-based detectors to form a long triangulation baseline, and by itself for the early warning of merger events. Such an accurate location measurement is the key for using GW signals as standard sirens for constraining the Hubble constant. This kind of detector also opens up the possibility to test type Ia supernovae progenitor hypotheses by constraining the merger rates of white dwarf binaries with both super- and sub-Chandrasekhar masses separately. We will discuss other scientific outcomes that can be delivered, including the constraint of structure formation in the early Universe, the search for intermediate-mass black holes, the precise determination of black hole spins, the probe of binary systems' orbital eccentricity evolution, and the detection of tertiary masses around merging binaries.
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“A Joint Fermi-GBM and LIGO/Virgo Analysis of Compact Binary Mergers From the First and Second Gravitational-wave Observing Runs”, Astrophysical Journal (2020).
R. Hamburg, C. Fletcher, E. Burns, A. Goldstein, and E. Bissaldi, et al.Abstract
We present results from offline searches of Fermi Gamma-ray Burst Monitor (GBM) data for gamma-ray transients coincident with the compact binary coalescences observed by the gravitational-wave (GW) detectors Advanced LIGO and Advanced Virgo during their first and second observing runs. In particular, we perform follow-up for both confirmed events and low significance candidates reported in the LIGO/Virgo catalog GWTC-1. We search for temporal coincidences between these GW signals and GBM-triggered gamma-ray bursts (GRBs). We also use the GBM Untargeted and Targeted subthreshold searches to find coincident gamma-rays below the onboard triggering threshold. This work implements a refined statistical approach by incorporating GW astrophysical source probabilities and GBM visibilities of LIGO/Virgo sky localizations to search for cumulative signatures of coincident subthreshold gamma-rays. All search methods recover the short gamma-ray burst GRB 170817A occurring ~1.7 s after the binary neutron-star merger GW170817. We also present results from a new search seeking GBM counterparts to LIGO single-interferometer triggers. This search finds a candidate joint event, but given the nature of the GBM signal and localization, as well as the high joint false alarm rate of 1.1 × 10⁻⁶ Hz, we do not consider it an astrophysical association. We find no additional coincidences.
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“A Cryogenic Silicon Interferometer for Gravitational-wave Detection”, Classical and Quantum Gravity (2020).
R. X. Adhikari, Odylio Aguiar, K. Arai, Bryan Barr, and Riccardo Bassiri, et al.Abstract
The detection of gravitational waves from compact binary mergers by LIGO has opened the era of gravitational wave astronomy, revealing a previously hidden side of the cosmos. To maximize the reach of the existing LIGO observatory facilities, we have designed a new instrument able to detect gravitational waves at distances 5 times further away than possible with Advanced LIGO, or at greater than 100 times the event rate. Observations with this new instrument will make possible dramatic steps toward understanding the physics of the nearby Universe, as well as observing the Universe out to cosmological distances by the detection of binary black hole coalescences. This article presents the instrument design and a quantitative analysis of the anticipated noise floor.
2019
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“The US Program in Ground-Based Gravitational Wave Science: Contribution from the LIGO Laboratory”, (2019).
David Reitze, Richard Abbott, Carl Adams, Rana Adhikari, and Nancy Aggarwal, et al.Abstract
Recent gravitational-wave observations from the LIGO and Virgo observatories have brought a sense of great excitement to scientists and citizens the world over. Since September 2015,10 binary black hole coalescences and one binary neutron star coalescence have been observed. They have provided remarkable, revolutionary insight into the "gravitational Universe" and have greatly extended the field of multi-messenger astronomy. At present, Advanced LIGO can see binary black hole coalescences out to redshift 0.6 and binary neutron star coalescences to redshift 0.05. This probes only a very small fraction of the volume of the observable Universe. However, current technologies can be extended to construct "3rd Generation" (3G) gravitational-wave observatories that would extend our reach to the very edge of the observable Universe. The event rates over such a large volume would be in the hundreds of thousands per year (i.e. tens per hour). Such 3G detectors would have a 10-fold improvement in strain sensitivity over the current generation of instruments, yielding signal-to-noise ratios of 1000 for events like those already seen. Several concepts are being studied for which engineering studies and reliable cost estimates will be developed in the next 5 years.
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“Tests of General Relativity with the Binary Black Hole Signals from the LIGO-Virgo Catalog GWTC-1”, Physical Review D (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
The detection of gravitational waves by Advanced LIGO and Advanced Virgo provides an opportunity to test general relativity in a regime that is inaccessible to traditional astronomical observations and laboratory tests. We present four tests of the consistency of the data with binary black hole gravitational waveforms predicted by general relativity. One test subtracts the best-fit waveform from the data and checks the consistency of the residual with detector noise. The second test checks the consistency of the low- and high-frequency parts of the observed signals. The third test checks that phenomenological deviations introduced in the waveform model (including in the post-Newtonian coefficients) are consistent with 0. The fourth test constrains modifications to the propagation of gravitational waves due to a modified dispersion relation, including that from a massive graviton. We present results both for individual events and also results obtained by combining together particularly strong events from the first and second observing runs of Advanced LIGO and Advanced Virgo, as collected in the catalog GWTC-1. We do not find any inconsistency of the data with the predictions of general relativity and improve our previously presented combined constraints by factors of 1.1 to 2.5. In particular, we bound the mass of the graviton to be m_g ≤ 4.7×10⁻²³ eV/c² (90% credible level), an improvement of a factor of 1.6 over our previously presented results. Additionally, we check that the four gravitational-wave events published for the first time in GWTC-1 do not lead to stronger constraints on alternative polarizations than those published previously.
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“Tests of General Relativity with GW170817”, Physical Review Letters (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
The recent discovery by Advanced LIGO and Advanced Virgo of a gravitational wave signal from a binary neutron star inspiral has enabled tests of general relativity (GR) with this new type of source. This source, for the first time, permits tests of strong-field dynamics of compact binaries in the presence of matter. In this Letter, we place constraints on the dipole radiation and possible deviations from GR in the post-Newtonian coefficients that govern the inspiral regime. Bounds on modified dispersion of gravitational waves are obtained; in combination with information from the observed electromagnetic counterpart we can also constrain effects due to large extra dimensions. Finally, the polarization content of the gravitational wave signal is studied. The results of all tests performed here show good agreement with GR.
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“Systematic calibration error requirements for gravitational-wave detectors via the Cramér-Rao bound”, Classical and Quantum Gravity (2019).
Evan D. Hall, Craig Cahillane, Kiwamu Izumi, Rory J. E. Smith, and Rana X. AdhikariAbstract
Gravitational-wave (GW) laser interferometers such as Advanced LIGO (The LIGO Scientific Collaboration 2015 Class. Quantum Grav. 32 074001) transduce spacetime strain into optical power fluctuation. Converting this optical power fluctuation back into an estimated spacetime strain requires a calibration process that accounts for both the interferometer's optomechanical response and the feedback control loop used to control the interferometer test masses. Systematic errors in the calibration parameters lead to systematic errors in the GW strain estimate, and hence to systematic errors in the astrophysical parameter estimates in a particular GW signal. In this work we examine this effect for a GW signal similar to GW150914, both for a low-power detector operation similar to the first and second Advanced LIGO observing runs and for a higher-power operation with detuned signal extraction. We set requirements on the accuracy of the calibration such that the astrophysical parameter estimation is limited by errors introduced by random detector noise, rather than calibration systematics. We also examine the impact of systematic calibration errors on the possible detection of a massive graviton.
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“Searches for Gravitational Waves from Known Pulsars at Two Harmonics in 2015-2017 LIGO Data”, Astrophysical Journal (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
We present a search for gravitational waves from 222 pulsars with rotation frequencies ≳10 Hz. We use advanced LIGO data from its first and second observing runs spanning 2015–2017, which provides the highest-sensitivity gravitational-wave data so far obtained. In this search we target emission from both the l = m = 2 mass quadrupole mode, with a frequency at twice that of the pulsar's rotation, and the l = 2, m = 1 mode, with a frequency at the pulsar rotation frequency. The search finds no evidence for gravitational-wave emission from any pulsar at either frequency. For the l = m = 2 mode search, we provide updated upper limits on the gravitational-wave amplitude, mass quadrupole moment, and fiducial ellipticity for 167 pulsars, and the first such limits for a further 55. For 20 young pulsars these results give limits that are below those inferred from the pulsars' spin-down. For the Crab and Vela pulsars our results constrain gravitational-wave emission to account for less than 0.017% and 0.18% of the spin-down luminosity, respectively. For the recycled millisecond pulsar J0711−6830 our limits are only a factor of 1.3 above the spin-down limit, assuming the canonical value of 10^(38) kg m^2 for the star's moment of inertia, and imply a gravitational-wave-derived upper limit on the star's ellipticity of 1.2 × 10^(−8). We also place new limits on the emission amplitude at the rotation frequency of the pulsars.
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“Searches for Continuous Gravitational Waves from 15 Supernova Remnants and Fomalhaut b with Advanced LIGO”, Astrophysical Journal (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
We describe directed searches for continuous gravitational waves (GWs) from 16 well-localized candidate neutron stars, assuming none of the stars has a binary companion. The searches were directed toward 15 supernova remnants and Fomalhaut b, a directly imaged extrasolar planet candidate that has been suggested to be a nearby old neutron star. Each search covered a broad band of frequencies and first and second time derivatives. After coherently integrating spans of data from the first Advanced LIGO observing run of 3.5–53.7 days per search, applying data-based vetoes, and discounting known instrumental artifacts, we found no astrophysical signals. We set upper limits on intrinsic GW strain as strict as 1 × 10^(−25), fiducial neutron star ellipticity as strict as 2 × 10^(−9), and fiducial r-mode amplitude as strict as 3 × 10^(−8).
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“Search for Transient Gravitational-wave Signals Associated with Magnetar Bursts during Advanced LIGO's Second Observing Run”, Astrophysical Journal (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
We present the results of a search for short- and intermediate-duration gravitational-wave signals from four magnetar bursts in Advanced LIGO's second observing run. We find no evidence of a signal and set upper bounds on the root sum squared of the total dimensionless strain (h_(rss)) from incoming intermediate-duration gravitational waves ranging from 1.1 × 10^(−22) at 150 Hz to 4.4 × 10^(−22) at 1550 Hz at 50% detection efficiency. From the known distance to the magnetar SGR 1806–20 (8.7 kpc), we can place upper bounds on the isotropic gravitational-wave energy of 3.4 × 10^(44) erg at 150 Hz assuming optimal orientation. This represents an improvement of about a factor of 10 in strain sensitivity from the previous search for such signals, conducted during initial LIGO's sixth science run. The short-duration search yielded upper limits of 2.1 × 10^(44) erg for short white noise bursts, and 2.3 × 10^(47) erg for 100 ms long ringdowns at 1500 Hz, both at 50% detection efficiency.
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“Search for the isotropic stochastic background using data from Advanced LIGO's second observing run”, Physical Review D (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
The stochastic gravitational-wave background is a superposition of sources that are either too weak or too numerous to detect individually. In this study we present the results from a cross-correlation analysis on data from Advanced LIGO's second observing run (O2), which we combine with the results of the first observing run (O1). We do not find evidence for a stochastic background, so we place upper limits on the normalized energy density in gravitational waves at the 95% credible level of Ω_(GW) < 6.0×10^(-8) for a frequency-independent (flat) background and Ω_(GW) < 4.8×10^(-8) at 25 Hz for a background of compact binary coalescences. The upper limit improves over the O1 result by a factor of 2.8. Additionally, we place upper limits on the energy density in an isotropic background of scalar- and vector-polarized gravitational waves, and we discuss the implication of these results for models of compact binaries and cosmic string backgrounds. Finally, we present a conservative estimate of the correlated broadband noise due to the magnetic Schumann resonances in O2, based on magnetometer measurements at both the LIGO Hanford and LIGO Livingston observatories. We find that correlated noise is well below the O2 sensitivity.
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“Search for Subsolar Mass Ultracompact Binaries in Advanced LIGO's Second Observing Run”, Physical Review Letters (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, S. Anand, and A. Ananyeva, et al.Abstract
We present an Advanced LIGO and Advanced Virgo search for sub-solar mass ultracompact objects in data obtained during Advanced LIGO's second observing run. In contrast to a previous search of Advanced LIGO data from the first observing run, this search includes the effects of component spin on the gravitational waveform. We identify no viable gravitational wave candidates consistent with sub-solar mass ultracompact binaries with at least one component between 0.2 - 1.0_⊙. We use the null result to constrain the binary merger rate of (0.2_⊙, 0.2_⊙) binaries to be less than 3.7 x 10⁵ Gpc⁻³ yr⁻¹ and the binary merger rate of (1.0⊙, 1.0_⊙) binaries to be less than 5.2 x 10³ Gpc⁻³ yr⁻¹. Sub-solar mass ultracompact objects are not expected to form via known stellar evolution channels, though it has been suggested that primordial density fluctuations or particle dark matter with cooling mechanisms and/or nuclear interactions could form black holes with sub-solar masses. Assuming a particular primordial black hole formation model, we constrain a population of merging 0.2_⊙ black holes to account for less than 16% of the dark matter density and a population of merging 1.0_⊙ black holes to account for less than 2% of the dark matter density. We discuss how constraints on the merger rate and dark matter fraction may be extended to arbitrary black hole population models that predict sub-solar mass binaries.
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“Search for intermediate mass black hole binaries in the first and second observing runs of the Advanced LIGO and Virgo network”, Physical Review D (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, S. Anand, and A. Ananyeva, et al.Abstract
Gravitational-wave astronomy has been firmly established with the detection of gravitational waves from the merger of ten stellar-mass binary black holes and a neutron star binary. This paper reports on the all-sky search for gravitational waves from intermediate mass black hole binaries in the first and second observing runs of the Advanced LIGO and Virgo network. The search uses three independent algorithms: two based on matched filtering of the data with waveform templates of gravitational-wave signals from compact binaries, and a third, model-independent algorithm that employs no signal model for the incoming signal. No intermediate mass black hole binary event is detected in this search. Consequently, we place upper limits on the merger rate density for a family of intermediate mass black hole binaries. In particular, we choose sources with total masses M = m_1+m_2 ∈ [120,800] M⊙ and mass ratios q = m_2/m_1 ∈ [0.1,1.0]. For the first time, this calculation is done using numerical relativity waveforms (which include higher modes) as models of the real emitted signal. We place a most stringent upper limit of 0.20 Gpc^(−3) yr^(−1) (in comoving units at the 90% confidence level) for equal-mass binaries with individual masses m_(1,2) = 100 M⊙ and dimensionless spins χ_(1,2) = 0.8 aligned with the orbital angular momentum of the binary. This improves by a factor of ∼5 that reported after Advanced LIGO's first observing run.
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“Search for Gravitational-wave Signals Associated with Gamma-Ray Bursts during the Second Observing Run of Advanced LIGO and Advanced Virgo”, Astrophysical Journal (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, S. Anand, and A. Ananyeva, et al.Abstract
We present the results of targeted searches for gravitational-wave transients associated with gamma-ray bursts during the second observing run of Advanced LIGO and Advanced Virgo, which took place from 2016 November to 2017 August. We have analyzed 98 gamma-ray bursts using an unmodeled search method that searches for generic transient gravitational waves and 42 with a modeled search method that targets compact-binary mergers as progenitors of short gamma-ray bursts. Both methods clearly detect the previously reported binary merger signal GW170817, with p-values of <9.38 × 10⁻⁶ (modeled) and 3.1 × 10⁻⁴ (unmodeled). We do not find any significant evidence for gravitational-wave signals associated with the other gamma-ray bursts analyzed, and therefore we report lower bounds on the distance to each of these, assuming various source types and signal morphologies. Using our final modeled search results, short gamma-ray burst observations, and assuming binary neutron star progenitors, we place bounds on the rate of short gamma-ray bursts as a function of redshift for z ≤ 1. We estimate 0.07–1.80 joint detections with Fermi-GBM per year for the 2019–20 LIGO-Virgo observing run and 0.15–3.90 per year when current gravitational-wave detectors are operating at their design sensitivities.
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“Search for gravitational waves from Scorpius X-1 in the second Advanced LIGO observing run with an improved hidden Markov model”, Physical Review D (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
We present results from a semicoherent search for continuous gravitational waves from the low-mass X-ray binary Scorpius X-1, using a hidden Markov model (HMM) to track spin wandering. This search improves on previous HMM-based searches of LIGO data by using an improved frequency domain matched filter, the J-statistic, and by analysing data from Advanced LIGO's second observing run. In the frequency range searched, from 60 to 650Hz, we find no evidence of gravitational radiation. At 194.6Hz, the most sensitive search frequency, we report an upper limit on gravitational wave strain (at 95% confidence) of h^(95%)_0 = 3.47×10^(⁻²⁵) when marginalising over source inclination angle. This is the most sensitive search for Scorpius X-1, to date, that is specifically designed to be robust in the presence of spin wandering.
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“Search for Gravitational Waves from a Long-lived Remnant of the Binary Neutron Star Merger GW170817”, Astrophysical Journal (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
One unanswered question about the binary neutron star coalescence GW170817 is the nature of its post-merger remnant. A previous search for post-merger gravitational waves targeted high-frequency signals from a possible neutron star remnant with a maximum signal duration of 500 s. Here, we revisit the neutron star remnant scenario and focus on longer signal durations, up until the end of the second Advanced LIGO-Virgo observing run, which was 8.5 days after the coalescence of GW170817. The main physical scenario for this emission is the power-law spindown of a massive magnetar-like remnant. We use four independent search algorithms with varying degrees of restrictiveness on the signal waveform and different ways of dealing with noise artefacts. In agreement with theoretical estimates, we find no significant signal candidates. Through simulated signals, we quantify that with the current detector sensitivity, nowhere in the studied parameter space are we sensitive to a signal from more than 1 Mpc away, compared to the actual distance of 40 Mpc. However, this study serves as a prototype for post-merger analyses in future observing runs with expected higher sensitivity.
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“Search for Eccentric Binary Black Hole Mergers with Advanced LIGO and Advanced Virgo during Their First and Second Observing Runs”, Astrophysical Journal (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, S. Anand, and A. Ananyeva, et al.Abstract
When formed through dynamical interactions, stellar-mass binary black holes (BBHs) may retain eccentric orbits (e > 0.1 at 10 Hz) detectable by ground-based gravitational-wave detectors. Eccentricity can therefore be used to differentiate dynamically formed binaries from isolated BBH mergers. Current template-based gravitational-wave searches do not use waveform models associated with eccentric orbits, rendering the search less efficient for eccentric binary systems. Here we present the results of a search for BBH mergers that inspiral in eccentric orbits using data from the first and second observing runs (O1 and O2) of Advanced LIGO and Advanced Virgo. We carried out the search with the coherent WaveBurst algorithm, which uses minimal assumptions on the signal morphology and does not rely on binary waveform templates. We show that it is sensitive to binary mergers with a detection range that is weakly dependent on eccentricity for all bound systems. Our search did not identify any new binary merger candidates. We interpret these results in light of eccentric binary formation models. We rule out formation channels with rates ≳100 Gpc^(−3) yr^(−1) for e > 0.1, assuming a black hole mass spectrum with a power-law index ≾2.
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“Quantum-Enhanced Advanced LIGO Detectors in the Era of Gravitational-Wave Astronomy”, Physical Review Letters (2019).
M. Tse, F. Matichard, R. Abbott, R. X. Adhikari, and A. Ananyeva, et al.Abstract
The Laser Interferometer Gravitational Wave Observatory (LIGO) has been directly detecting gravitational waves from compact binary mergers since 2015. We report on the first use of squeezed vacuum states in the direct measurement of gravitational waves with the Advanced LIGO H1 and L1 detectors. This achievement is the culmination of decades of research to implement squeezed states in gravitational-wave detectors. During the ongoing O3 observation run, squeezed states are improving the sensitivity of the LIGO interferometers to signals above 50 Hz by up to 3 dB, thereby increasing the expected detection rate by 40% (H1) and 50% (L1).
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“Properties of the Binary Neutron Star Merger GW170817”, Physical Review X (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
On August 17, 2017, the Advanced LIGO and Advanced Virgo gravitational-wave detectors observed a low-mass compact binary inspiral. The initial sky localization of the source of the gravitational-wave signal, GW170817, allowed electromagnetic observatories to identify NGC 4993 as the host galaxy. In this work, we improve initial estimates of the binary's properties, including component masses, spins, and tidal parameters, using the known source location, improved modeling, and recalibrated Virgo data. We extend the range of gravitational-wave frequencies considered down to 23 Hz, compared to 30 Hz in the initial analysis. We also compare results inferred using several signal models, which are more accurate and incorporate additional physical effects as compared to the initial analysis. We improve the localization of the gravitational-wave source to a 90% credible region of 16 deg^2. We find tighter constraints on the masses, spins, and tidal parameters, and continue to find no evidence for nonzero component spins. The component masses are inferred to lie between 1.00 and 1.89 M⊙ when allowing for large component spins, and to lie between 1.16 and 1.60 M⊙ (with a total mass 2.73^(+0.04)_(−0.01) M⊙) when the spins are restricted to be within the range observed in Galactic binary neutron stars. Using a precessing model and allowing for large component spins, we constrain the dimensionless spins of the components to be less than 0.50 for the primary and 0.61 for the secondary. Under minimal assumptions about the nature of the compact objects, our constraints for the tidal deformability parameter ˜Λ are (0,630) when we allow for large component spins, and 300^(+420)_(−230_ (using a 90% highest posterior density interval) when restricting the magnitude of the component spins, ruling out several equation-of-state models at the 90% credible level. Finally, with LIGO and GEO600 data, we use a Bayesian analysis to place upper limits on the amplitude and spectral energy density of a possible postmerger signal.
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“Narrow-band search for gravitational waves from known pulsars using the second LIGO observing run”, Physical Review D (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
Isolated spinning neutron stars, asymmetric with respect to their rotation axis, are expected to be sources of continuous gravitational waves. The most sensitive searches for these sources are based on accurate matched filtering techniques, that assume the continuous wave to be phase-locked with the pulsar beamed emission. While matched filtering maximizes the search sensitivity, a significant signal-to-noise ratio loss will happen in case of a mismatch between the assumed and the true signal phase evolution. Narrow-band algorithms allow for a small mismatch in the frequency and spin-down values of the pulsar while integrating coherently the entire data set. In this paper we describe a narrow-band search using LIGO O2 data for the continuous wave emission of 33 pulsars. No evidence for a continuous wave signal has been found and upper-limits on the gravitational wave amplitude, over the analyzed frequency and spin-down volume, have been computed for each of the targets. In this search we have surpassed the spin-down limit for some of the pulsars already present in the O1 LIGO narrow-band search, such as J1400-6325 J1813-1246, J1833-1034, J1952+3252, and for new targets such as J0940-5428 and J1747-2809. For J1400-6325, J1833-1034 and J1747-2809 this is the first time the spin-down limit is surpassed.
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“Low-latency Gravitational-wave Alerts for Multimessenger Astronomy during the Second Advanced LIGO and Virgo Observing Run”, Astrophysical Journal (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
Advanced LIGO's second observing run (O2), conducted from 2016 November 30 to 2017 August 25, combined with Advanced Virgo's first observations in 2017 August, witnessed the birth of gravitational-wave multimessenger astronomy. The first ever gravitational-wave detection from the coalescence of two neutron stars, GW170817, and its gamma-ray counterpart, GRB 170817A, led to an electromagnetic follow-up of the event at an unprecedented scale. Several teams from across the world searched for EM/neutrino counterparts to GW170817, paving the way for the discovery of optical, X-ray, and radio counterparts. In this article, we describe the online identification of gravitational-wave transients and the distribution of gravitational-wave alerts by the LIGO and Virgo collaborations during O2. We also describe the gravitational-wave observables that were sent in the alerts to enable searches for their counterparts. Finally, we give an overview of the online candidate alerts shared with observing partners during O2. Alerts were issued for 14 candidates, 6 of which have been confirmed as gravitational-wave events associated with the merger of black holes or neutron stars. Of the 14 alerts, 8 were issued less than an hour after data acquisition.
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“Improving astrophysical parameter estimation via offline noise subtraction for Advanced LIGO”, Physical Review D (2019).
J. C. Driggers, B. P. Abbott, R. Abbott, R. X. Adhikari, and A. Ananyeva, et al.Abstract
The Advanced LIGO detectors have recently completed their second observation run successfully. The run lasted for approximately 10 months and led to multiple new discoveries. The sensitivity to gravitational waves was partially limited by laser noise. Here, we utilize auxiliary sensors that witness these correlated noise sources, and use them for noise subtraction in the time domain data. This noise and line removal is particularly significant for the LIGO Hanford Observatory, where the improvement in sensitivity is greater than 20%. Consequently, we were also able to improve the astrophysical estimation for the location, masses, spins, and orbital parameters of the gravitational wave progenitors.
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“GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs”, Physical Review X (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
We present the results from three gravitational-wave searches for coalescing compact binaries with component masses above 1M_⊙ during the first and second observing runs of the Advanced gravitational-wave detector network. During the first observing run (O1), from September 12th, 2015 to January 19th, 2016, gravitational waves from three binary black hole mergers were detected. The second observing run (O2), which ran from November 30th, 2016 to August 25th, 2017, saw the first detection of gravitational waves from a binary neutron star inspiral, in addition to the observation of gravitational waves from a total of seven binary black hole mergers, four of which we report here for the first time: GW170729, GW170809, GW170818 and GW170823. For all significant gravitational-wave events, we provide estimates of the source properties. The detected binary black holes have total masses between 18.6^(+3.1)_(−0.7)M⊙, and 85.1^(+15.6)_(−10.9)M⊙, and range in distance between 320^(+120)_(−110) Mpc and 2750^(+1350)_(−1320) Mpc. No neutron star - black hole mergers were detected. In addition to highly significant gravitational-wave events, we also provide a list of marginal event candidates with an estimated false alarm rate less than 1 per 30 days. From these results over the first two observing runs, which include approximately one gravitational-wave detection per 15 days of data searched, we infer merger rates at the 90% confidence intervals of 110−3840 Gpc^(−3)y^(−1) for binary neutron stars and 9.7−101 Gpc^(−3)y^(−1) for binary black holes assuming fixed population distributions, and determine a neutron star - black hole merger rate 90% upper limit of 610 Gpc^(−3)y^(−1).
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“First Measurement of the Hubble Constant from a Dark Standard Siren using the Dark Energy Survey Galaxies and the LIGO/Virgo Binary–Black-hole Merger GW170814”, Astrophysical Journal Letters (2019).
M. Soares-Santos, B. P. Abbott, R. Abbott, R. X. Adhikari, and A. Ananyeva, et al.Abstract
We present a multi-messenger measurement of the Hubble constant H_0 using the binary–black-hole merger GW170814 as a standard siren, combined with a photometric redshift catalog from the Dark Energy Survey (DES). The luminosity distance is obtained from the gravitational wave signal detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO)/Virgo Collaboration (LVC) on 2017 August 14, and the redshift information is provided by the DES Year 3 data. Black hole mergers such as GW170814 are expected to lack bright electromagnetic emission to uniquely identify their host galaxies and build an object-by-object Hubble diagram. However, they are suitable for a statistical measurement, provided that a galaxy catalog of adequate depth and redshift completion is available. Here we present the first Hubble parameter measurement using a black hole merger. Our analysis results in H_0 = 75^(+40)_(−32) km s^(−1) Mpc^(−1), which is consistent with both SN Ia and cosmic microwave background measurements of the Hubble constant. The quoted 68% credible region comprises 60% of the uniform prior range [20, 140] km s−1 Mpc−1, and it depends on the assumed prior range. If we take a broader prior of [10, 220] km s−1 Mpc−1, we find H_0=78^(+96)_(−24) km s^(−1) Mpc^(−1) (57% of the prior range). Although a weak constraint on the Hubble constant from a single event is expected using the dark siren method, a multifold increase in the LVC event rate is anticipated in the coming years and combinations of many sirens will lead to improved constraints on H_0.
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“Exploring the sensitivity of gravitational wave detectors to neutron star physics”, Physical Review D (2019).
Denis Martynov, Haixing Miao, Huan Yang, Francisco Hernandez Vivanco, Eric Thrane, Rory Smith, Paul Lasky, William E. East, Rana Adhikari, Andreas Bauswein, Aidan Brooks, Yanbei Chen, Thomas Corbitt, Andreas Freise, Hartmut Grote, Yuri Levin, Chunnong Zhao, and Alberto VecchioAbstract
The physics of neutron stars can be studied with gravitational waves emitted from coalescing binary systems. Tidal effects become significant during the last few orbits and can be visible in the gravitational wave spectrum above 500 Hz. After the merger, the neutron star remnant oscillates at frequencies above 1 kHz and can collapse into a black hole. Gravitational wave detectors with a sensitivity of ≃ 10^(−24) strain/√Hz at 2–4 kHz can observe these oscillations from a source which is approximately 100 Mpc away. The current observatories, such as LIGO and Virgo, are limited by shot noise at high frequencies and have a sensitivity of greater than or equal to 2 × 10^(−23) strain/√Hz at 3 kHz. In this paper, we propose an optical configuration of gravitational wave detectors, which can be set up in present facilities using the current interferometer topology. This scheme has the potential to reach 7 × 10^(−25) strain/√Hz at 2.5 kHz without compromising the detector sensitivity to black hole binaries. We argue that the proposed instruments have the potential to detect similar amount of postmerger neutron star oscillations as the next generation detectors, such as Cosmic Explorer and Einstein Telescope. We also optimize the arm length of the future detectors for neutron star physics and find that the optimal arm length is ≈20 km. These instruments have the potential to observe neutron star postmerger oscillations at a rate of approximately 30 events per year with a signal-to-noise ratio of 5 or more.
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“Directional limits on persistent gravitational waves using data from Advanced LIGO's first two observing runs”, Physical Review D (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
We perform an unmodeled search for persistent, directional gravitational wave (GW) sources using data from the first and second observing runs of Advanced LIGO. We do not find evidence for any GW signals. We place limits on the broadband GW flux emitted at 25 Hz from point sources with a power law spectrum at F_α,Θ<(0.05–25)×10^(−8) erg cm^(−2) s^(−1) Hz−1 and the (normalized) energy density spectrum in GWs at 25 Hz from extended sources at Ω_α(Θ)<(0.19–2.89)×10^(−8) sr^(−1) where α is the spectral index of the energy density spectrum. These represent improvements of 2.5–3× over previous limits. We also consider point sources emitting GWs at a single frequency, targeting the directions of Sco X-1, SN 1987A, and the Galactic center. The best upper limits on the strain amplitude of a potential source in these three directions range from h_0<(3.6–4.7)×10^(−25), 1.5× better than previous limits set with the same analysis method. We also report on a marginally significant outlier at 36.06 Hz. This outlier is not consistent with a persistent gravitational-wave source as its significance diminishes when combining all of the available data.
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“Cosmic Explorer: The U.S. Contribution to Gravitational-Wave Astronomy beyond LIGO”, (2019).
David Reitze, Rana X. Adhikari, Stefan Ballmer, Barry Barish, and Lisa Barsotti, et al.Abstract
This white paper describes the research and development needed over the next decade to realize "Cosmic Explorer," the U.S. node of a future third-generation detector network that will be capable of observing and characterizing compact gravitational-wave sources to cosmological redshifts.
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“Constraining the p-Mode–g-Mode Tidal Instability with GW170817”, Physical Review Letters (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
We analyze the impact of a proposed tidal instability coupling p modes and g modes within neutron stars on GW170817. This nonresonant instability transfers energy from the orbit of the binary to internal modes of the stars, accelerating the gravitational-wave driven inspiral. We model the impact of this instability on the phasing of the gravitational wave signal using three parameters per star: an overall amplitude, a saturation frequency, and a spectral index. Incorporating these additional parameters, we compute the Bayes factor (ln B^(pg)_(!pg)) comparing our p−g model to a standard one. We find that the observed signal is consistent with waveform models that neglect p−g effects, with lnB^(pg)_(!pg) = 0.03^(+0.70)_(−0.58) (maximum a posteriori and 90% credible region). By injecting simulated signals that do not include p−geffects and recovering them with the p−g model, we show that there is a ≃50% probability of obtaining similar lnB^(pg)_(!pg) even when p−g effects are absent. We find that the p−g amplitude for 1.4 M⊙ neutron stars is constrained to less than a few tenths of the theoretical maximum, with maxima a posteriori near one-tenth this maximum and p−g saturation frequency ∼70 Hz. This suggests that there are less than a few hundred excited modes, assuming they all saturate by wave breaking. For comparison, theoretical upper bounds suggest ≲10^3 modes saturate by wave breaking. Thus, the measured constraints only rule out extreme values of the p−g parameters. They also imply that the instability dissipates ≲10^(51) erg over the entire inspiral, i.e., less than a few percent of the energy radiated as gravitational waves.
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“Binary Black Hole Population Properties Inferred from the First and Second Observing Runs of Advanced LIGO and Advanced Virgo”, Astrophysical Journal Letters (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, S. Anand, and A. Ananyeva, et al.Abstract
We present results on the mass, spin, and redshift distributions of the ten binary black hole mergers detected in the first and second observing runs completed by Advanced LIGO and Advanced Virgo. We constrain properties of the binary black hole (BBH) mass spectrum using models with a range of parameterizations of the BBH mass and spin distributions. We find that the mass distribution of the more massive black hole in such binaries is well approximated by models with no more than 1% of black holes more massive than 45M⊙, and a power law index of α=1.6^(+1.5)_(−1.7) (90% credibility). We also show that BBHs are unlikely to be composed of black holes with large spins aligned to the orbital angular momentum. Modelling the evolution of the BBH merger rate with redshift, we show that it is flat or increasing with redshift with 88% probability. Marginalizing over uncertainties in the BBH population, we find robust estimates of the BBH merger rate density of R=53.2^(+58.5)_(−28.8) Gpc^(-3) yr^(-1) (90% credibility). As the BBH catalog grows in future observing runs, we expect that uncertainties in the population model parameters will shrink, potentially providing insights into the formation of black holes via supernovae, binary interactions of massive stars, stellar cluster dynamics, and the formation history of black holes across cosmic time.
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“Astrophysics and cosmology with a deci-hertz gravitational-wave detector: TianGO”, (2019).
Kevin A. Kuns, Hang Yu, Yanbei Chen, and Rana X. AdhikariAbstract
We present the astrophysical science case for a space-based, deci-Hz gravitational-wave (GW) detector. We particularly highlight an ability in inferring a source's sky location, both when combined with a network of ground-based detectors to form a long triangulation baseline, and by itself for the early warning of merger events. Such an accurate location measurement is the key for using GW signals as standard sirens for constraining the Hubble constant. This kind of detector also opens up the possibility of testing type Ia supernovae progenitor hypotheses by constraining the merger rates of white dwarf binaries with both super- and sub-Chandrasekhar masses separately. We will discuss other scientific outcomes that can be delivered, including the precise determination of black hole spins, the constraint of structure formation in the early Universe, and the search for intermediate-mass black holes.
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“Astrophysical science metrics for next-generation gravitational-wave detectors”, Classical and Quantum Gravity (2019).
R. X. Adhikari, P. Ajith, Y. Chen, J. A. Clark, V. Dergachev, N. V. Fotopoulos, S. E. Gossan, I. Mandel, M. Okounkova, V. Raymond, and J. S. ReadAbstract
The second generation of gravitational-wave (GW) detectors are being built and tuned all over the world. The detection of signals from binary black holes is beginning to fulfil the promise of GW astronomy. In this work, we examine several possible configurations for third-generation laser interferometers in existing km-scale facilities. We propose a set of astrophysically motivated metrics to evaluate detector performance. We measure the impact of detector design choices against these metrics, providing a quantitative cost-benefit analyses of the resulting scientific payoffs.
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“Apparatus to Measure Optical Scatter of Coatings Versus Annealing Temperature”, (2019).
Joshua R. Smith, Rana X. Adhikari, Katerin M. Aleman, Adrian Avila-Alvarez, Garilynn Billingsley, Amy Gleckl, Jazlyn Guerrero, Ashot Markosyan, Steven D. Penn, Juan A. Rocha, Dakota Rose, and Robert WrightAbstract
Light scattered by amorphous thin-film optical coatings limits the sensitivity of interferometric gravitational-wave detectors. We describe an imaging scatterometer to assess the role that crystal growth during annealing plays in this scatter.
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“All-sky search for short gravitational-wave bursts in the second Advanced LIGO and Advanced Virgo run”, Physical Review D (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, S. Anand, and A. Ananyeva, et al.Abstract
We present the results of a search for short-duration gravitational-wave transients in the data from the second observing run of Advanced LIGO and Advanced Virgo. We search for gravitational-wave transients with a duration of milliseconds to approximately one second in the 32–4096 Hz frequency band with minimal assumptions about the signal properties, thus targeting a wide variety of sources. We also perform a matched-filter search for gravitational-wave transients from cosmic string cusps for which the waveform is well modeled. The unmodeled search detected gravitational waves from several binary black hole mergers which have been identified by previous analyses. No other significant events have been found by either the unmodeled search or the cosmic string search. We thus present the search sensitivities for a variety of signal waveforms and report upper limits on the source rate density as a function of the characteristic frequency of the signal. These upper limits are a factor of 3 lower than the first observing run, with a 50% detection probability for gravitational-wave emissions with energies of ∼10^(−9) M⊙c^2 at 153 Hz. For the search dedicated to cosmic string cusps we consider several loop distribution models, and present updated constraints from the same search done in the first observing run.
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“All-sky search for long-duration gravitational-wave transients in the second Advanced LIGO observing run”, Physical Review D (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
We present the results of a search for long-duration gravitational-wave transients in the data from the Advanced LIGO second observation run; we search for gravitational-wave transients of 2 -- 500~s duration in the 24−2048\,Hz frequency band with minimal assumptions about signal properties such as waveform morphologies, polarization, sky location or time of occurrence. Targeted signal models include fallback accretion onto neutron stars, broadband chirps from innermost stable circular orbit waves around rotating black holes, eccentric inspiral-merger-ringdown compact binary coalescence waveforms, and other models. The second observation run totals about \otwoduration~days of coincident data between November 2016 and August 2017. We find no significant events within the parameter space that we searched, apart from the already-reported binary neutron star merger GW170817. We thus report sensitivity limits on the root-sum-square strain amplitude h_(rss) at 50% efficiency. These sensitivity estimates are an improvement relative to the first observing run and also done with an enlarged set of gravitational-wave transient waveforms. Overall, the best search sensitivity is h^(50%)_(rss) = 2.7×10^(−22)~Hz^(−1/2) for a millisecond magnetar model. For eccentric compact binary coalescence signals, the search sensitivity reaches h^(50%)_(rss) = 9.6×10^(−22)~Hz^(−1/2).
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“All-sky search for continuous gravitational waves from isolated neutron stars using Advanced LIGO O2 data”, Physical Review D (2019).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
We present results of an all-sky search for continuous gravitational waves (CWs), which can be produced by fast spinning neutron stars with an asymmetry around their rotation axis, using data from the second observing run of the Advanced LIGO detectors. Three different semicoherent methods are used to search in a gravitational-wave frequency band from 20 to 1922 Hz and a first frequency derivative from −1×10^(−8) to 2×10^(−9) Hz/s. None of these searches has found clear evidence for a CW signal, so upper limits on the gravitational-wave strain amplitude are calculated, which for this broad range in parameter space are the most sensitive ever achieved.
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“A Fermi Gamma-Ray Burst Monitor Search for Electromagnetic Signals Coincident with Gravitational-wave Candidates in Advanced LIGO's First Observing Run”, Astrophysical Journal (2019).
E. Burns, B. P. Abbott, R. Abbott, R. X. Adhikari, and A. Ananyeva, et al.Abstract
We present a search for prompt gamma-ray counterparts to compact binary coalescence gravitational wave (GW) candidates from Advanced LIGO's first observing run (O1). As demonstrated by the multimessenger observations of GW170817/GRB 170817A, electromagnetic and GW observations provide complementary information about the astrophysical source, and in the case of weaker candidates, may strengthen the case for an astrophysical origin. Here we investigate low-significance GW candidates from the O1 compact binary coalescence searches using the Fermi Gamma-Ray Burst Monitor (GBM), leveraging its all sky and broad energy coverage. Candidates are ranked and compared to background to measure the significance. Those with false alarm rates (FARs) of less than 10^(−5) Hz (about one per day, yielding a total of 81 candidates) are used as the search sample for gamma-ray follow-up. No GW candidates were found to be coincident with gamma-ray transients independently identified by blind searches of the GBM data. In addition, GW candidate event times were followed up by a separate targeted search of GBM data. Among the resulting GBM events, the two with the lowest FARs were the gamma-ray transient GW150914-GBM presented in Connaughton et al. and a solar flare in chance coincidence with a GW candidate.
2018
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“Search for Tensor, Vector, and Scalar Polarizations in the Stochastic Gravitational-Wave Background”, Physical Review Letters (2018).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
The detection of gravitational waves with Advanced LIGO and Advanced Virgo has enabled novel tests of general relativity, including direct study of the polarization of gravitational waves. While general relativity allows for only two tensor gravitational-wave polarizations, general metric theories can additionally predict two vector and two scalar polarizations. The polarization of gravitational waves is encoded in the spectral shape of the stochastic gravitational-wave background, formed by the superposition of cosmological and individually unresolved astrophysical sources. Using data recorded by Advanced LIGO during its first observing run, we search for a stochastic background of generically polarized gravitational waves. We find no evidence for a background of any polarization, and place the first direct bounds on the contributions of vector and scalar polarizations to the stochastic background. Under log-uniform priors for the energy in each polarization, we limit the energy densities of tensor, vector, and scalar modes at 95% credibility to Ω^T_0 < 5.58×10^(−8), Ω^V_0 < 6.35×10^(−8), and Ω^S_0 < 1.08×10^(−7) at a reference frequency f_0=25 Hz.
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“Search for Subsolar-Mass Ultracompact Binaries in Advanced LIGO's First Observing Run”, Physical Review Letters (2018).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
We present the first Advanced LIGO and Advanced Virgo search for ultracompact binary systems with component masses between 0.2 M⊙–1.0 M⊙ using data taken between September 12, 2015 and January 19, 2016. We find no viable gravitational wave candidates. Our null result constrains the coalescence rate of monochromatic (delta function) distributions of nonspinning (0.2 M⊙, 0.2 M⊙) ultracompact binaries to be less than 1.0×10^6 Gpc^(−3) yr^(−1) and the coalescence rate of a similar distribution of (1.0 M⊙, 1.0 M⊙) ultracompact binaries to be less than 1.9×10^4 Gpc^(−3) yr^(−1) (at 90% confidence). Neither black holes nor neutron stars are expected to form below ∼1 M⊙ through conventional stellar evolution, though it has been proposed that similarly low mass black holes could be formed primordially through density fluctuations in the early Universe and contribute to the dark matter density. The interpretation of our constraints in the primordial black hole dark matter paradigm is highly model dependent; however, under a particular primordial black hole binary formation scenario we constrain monochromatic primordial black hole populations of 0.2 M⊙ to be less than 33% of the total dark matter density and monochromatic populations of 1.0 M⊙ to be less than 5% of the dark matter density. The latter strengthens the presently placed bounds from microlensing surveys of massive compact halo objects (MACHOs) provided by the MACHO and EROS Collaborations.
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“Prospects for observing and localizing gravitational-wave transients with Advanced LIGO, Advanced Virgo and KAGRA”, Living Reviews in Relativity (2018).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
We present possible observing scenarios for the Advanced LIGO, Advanced Virgo and KAGRA gravitational-wave detectors over the next decade, with the intention of providing information to the astronomy community to facilitate planning for multi-messenger astronomy with gravitational waves. We estimate the sensitivity of the network to transient gravitational-wave signals, and study the capability of the network to determine the sky location of the source. We report our findings for gravitational-wave transients, with particular focus on gravitational-wave signals from the inspiral of binary neutron star systems, which are the most promising targets for multi-messenger astronomy. The ability to localize the sources of the detected signals depends on the geographical distribution of the detectors and their relative sensitivity, and 90% credible regions can be as large as thousands of square degrees when only two sensitive detectors are operational. Determining the sky position of a significant fraction of detected signals to areas of 5–20 deg^2 requires at least three detectors of sensitivity within a factor of ∼2 of each other and with a broad frequency bandwidth. When all detectors, including KAGRA and the third LIGO detector in India, reach design sensitivity, a significant fraction of gravitational-wave signals will be localized to a few square degrees by gravitational-wave observations alone.
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“Laser Interferometers as Dark Matter Detectors”, Physical Review D (2018).
Evan D. Hall, Rana X. Adhikari, Valery V. Frolov, Holger Müller, and Maxim PospelovAbstract
While the global cosmological and local galactic abundance of dark matter is well established, its identity, physical size, and composition remain a mystery. In this paper, we analyze an important question of dark matter detectability through its gravitational interaction, using current and next generation gravitational-wave observatories to look for macroscopic (kilogram-scale or larger) objects. Keeping the size of the dark matter objects to be smaller than the physical dimensions of the detectors, and keeping their mass as a free parameter, we derive the expected event rates. For favorable choice of mass, we find that dark matter interactions could be detected in space-based detectors such as LISA at a rate of one per ten years. We then assume the existence of an additional Yukawa force between dark matter and regular matter. By choosing the range of the force to be comparable to the size of the detectors, we derive the levels of sensitivity to such a new force, which exceeds the sensitivity of other probes in a wide range of parameters. For sufficiently large Yukawa coupling strength, the rate of dark matter events can then exceed 10 per year for both ground- and space-based detectors. Thus, gravitational-wave observatories can make an important contribution to a global effort of searching for nongravitational interactions of dark matter.
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“Identification and mitigation of narrow spectral artifacts that degrade searches for persistent gravitational waves in the first two observing runs of Advanced LIGO”, Physical Review D (2018).
P. B. Covas, T. A. Callister, M. W. Coughlin, J. McIver, and B. P. Abbott, et al.Abstract
Searches are under way in Advanced LIGO and Virgo data for persistent gravitational waves from continuous sources, e.g. rapidly rotating galactic neutron stars, and stochastic sources, e.g. relic gravitational waves from the Big Bang or superposition of distant astrophysical events such as mergers of black holes or neutron stars. These searches can be degraded by the presence of narrow spectral artifacts (lines) due to instrumental or environmental disturbances. We describe a variety of methods used for finding, identifying and mitigating these artifacts, illustrated with particular examples. Results are provided in the form of lists of line artifacts that can safely be treated as non-astrophysical. Such lists are used to improve the efficiencies and sensitivities of continuous and stochastic gravitational wave searches by allowing vetoes of false outliers and permitting data cleaning.
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“GW170817: Measurements of Neutron Star Radii and Equation of State”, Physical Review Letters (2018).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
On 17 August 2017, the LIGO and Virgo observatories made the first direct detection of gravitational waves from the coalescence of a neutron star binary system. The detection of this gravitational-wave signal, GW170817, offers a novel opportunity to directly probe the properties of matter at the extreme conditions found in the interior of these stars. The initial, minimal-assumption analysis of the LIGO and Virgo data placed constraints on the tidal effects of the coalescing bodies, which were then translated to constraints on neutron star radii. Here, we expand upon previous analyses by working under the hypothesis that both bodies were neutron stars that are described by the same equation of state and have spins within the range observed in Galactic binary neutron stars. Our analysis employs two methods: the use of equation-of-state-insensitive relations between various macroscopic properties of the neutron stars and the use of an efficient parametrization of the defining function p(ρ) of the equation of state itself. From the LIGO and Virgo data alone and the first method, we measure the two neutron star radii as R_1=10.8^(+2.0)_(−1.7) km for the heavier star and R_2=10.7^(+2.1)_(−1.5) km for the lighter star at the 90% credible level. If we additionally require that the equation of state supports neutron stars with masses larger than 1.97 M⊙ as required from electromagnetic observations and employ the equation-of-state parametrization, we further constrain R_1=11.9^(+1.4)_(−1.4) km and R_2=11.9^(+1.4)_(−1.4) km at the 90% credible level. Finally, we obtain constraints on p(ρ) at supranuclear densities, with pressure at twice nuclear saturation density measured at 3.5^(+2.7)_(−1.7)×10^(34) dyn cm^(−2) at the 90% level.
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“GW170817: Implications for the Stochastic Gravitational-Wave Backgroud from Compact Binary Coalescences”, Physical Review Letters (2018).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
The LIGO Scientific and Virgo Collaborations have announced the event GW170817, the first detection of gravitational waves from the coalescence of two neutron stars. The merger rate of binary neutron stars estimated from this event suggests that distant, unresolvable binary neutron stars create a significant astrophysical stochastic gravitational-wave background. The binary neutron star component will add to the contribution from binary black holes, increasing the amplitude of the total astrophysical background relative to previous expectations. In the Advanced LIGO-Virgo frequency band most sensitive to stochastic backgrounds (near 25 Hz), we predict a total astrophysical background with amplitude Ω_(GW)(f = 25 Hz) = 1.8^(+2.7)_(−1.3) × 10^(−9) with 90% confidence, compared with Ω_(GW)(f = 25 Hz) = 1.1^(+1.2)_(−0.7) × 10^(−9) from binary black holes alone. Assuming the most probable rate for compact binary mergers, we find that the total background may be detectable with a signal-to-noise-ratio of 3 after 40 months of total observation time, based on the expected timeline for Advanced LIGO and Virgo to reach their design sensitivity.
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“Full band all-sky search for periodic gravitational waves in the O1 LIGO data”, Physical Review D (2018).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
We report on a new all-sky search for periodic gravitational waves in the frequency band 475–2000 Hz and with a frequency time derivative in the range of [−1.0,+0.1]×10^(−8) Hz/s. Potential signals could be produced by a nearby spinning and slightly nonaxisymmetric isolated neutron star in our Galaxy. This search uses the data from Advanced LIGO's first observational run O1. No gravitational-wave signals were observed, and upper limits were placed on their strengths. For completeness, results from the separately published low-frequency search 20–475 Hz are included as well. Our lowest upper limit on worst-case (linearly polarized) strain amplitude h_0 is ∼4×10^(−25) near 170 Hz, while at the high end of our frequency range, we achieve a worst-case upper limit of 1.3×10^(−24). For a circularly polarized source (most favorable orientation), the smallest upper limit obtained is ∼1.5×10^(−25).
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“First Search for Nontensorial Gravitational Waves from Known Pulsars”, Physical Review Letters (2018).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
We present results from the first directed search for nontensorial gravitational waves. While general relativity allows for tensorial (plus and cross) modes only, a generic metric theory may, in principle, predict waves with up to six different polarizations. This analysis is sensitive to continuous signals of scalar, vector, or tensor polarizations, and does not rely on any specific theory of gravity. After searching data from the first observation run of the advanced LIGO detectors for signals at twice the rotational frequency of 200 known pulsars, we find no evidence of gravitational waves of any polarization. We report the first upper limits for scalar and vector strains, finding values comparable in magnitude to previously published limits for tensor strain. Our results may be translated into constraints on specific alternative theories of gravity.
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“External quantum efficiency enhancement by photon recycling with backscatter evasion”, Applied Optics (2018).
Koji Nagano, Antonio Perreca, Koji Arai, and Rana X. AdhikariAbstract
The nonunity quantum efficiency (QE) in photodiodes (PD) causes deterioration of signal quality in quantum optical experiments due to photocurrent loss as well as the introduction of vacuum fluctuations into the measurement. In this paper, we report that the external QE enhancement of a PD was demonstrated by recycling the reflected photons. The external QE for an InGaAs PD was increased by 0.01–0.06 from 0.86–0.92 over a wide range of incident angles. Moreover, we confirmed that this technique does not increase backscattered light when the recycled beam is properly misaligned.
Full text · DOI: 10.1364/ao.57.003372
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“Effects of data quality vetoes on a search for compact binary coalescences in Advanced LIGO's first observing run”, Classical and Quantum Gravity (2018).
B. P. Abbott, R. Abbott, R. X. Adhikari, S. B. Anderson, and K. Arai, et al.Abstract
The first observing run of Advanced LIGO spanned 4 months, from 12 September 2015 to 19 January 2016, during which gravitational waves were directly detected from two binary black hole systems, namely GW150914 and GW151226. Confident detection of gravitational waves requires an understanding of instrumental transients and artifacts that can reduce the sensitivity of a search. Studies of the quality of the detector data yield insights into the cause of instrumental artifacts and data quality vetoes specific to a search are produced to mitigate the effects of problematic data. In this paper, the systematic removal of noisy data from analysis time is shown to improve the sensitivity of searches for compact binary coalescences. The output of the PyCBC pipeline, which is a python-based code package used to search for gravitational wave signals from compact binary coalescences, is used as a metric for improvement. GW150914 was a loud enough signal that removing noisy data did not improve its significance. However, the removal of data with excess noise decreased the false alarm rate of GW151226 by more than two orders of magnitude, from 1 in 770 yr to less than 1 in 186 000 yr.
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“Effect of elevated substrate temperature deposition on the mechanical losses in tantala thin film coatings”, Classical and Quantum Gravity (2018).
G. Vajente, A. Ananyeva, G. Billingsley, E. Gustafson, A. Heptonstall, C. Torrie, and R. X. AdhikariAbstract
Brownian thermal noise in dielectric multilayer coatings limits the sensitivity of current and future interferometric gravitational wave detectors. In this work we explore the possibility of improving the mechanical losses of tantala, often used as the high refractive index material, by depositing it on a substrate held at elevated temperature. Promising results have been previously obtained with this technique when applied to amorphous silicon. We show that depositing tantala on a hot substrate reduced the mechanical losses of the as-deposited coating, but subsequent thermal treatments had a larger impact, as they reduced the losses to levels previously reported in the literature. We also show that the reduction in mechanical loss correlates with increased medium range order in the atomic structure of the coatings using x-ray diffraction and Raman spectroscopy. Finally, a discussion is included on our results, which shows that the elevated temperature deposition of pure tantala coatings does not appear to reduce mechanical loss in a similar way to that reported in the literature for amorphous silicon; and we suggest possible future research directions.
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“Constraints on cosmic strings using data from the first Advanced LIGO observing run”, Physical Review D (2018).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
Cosmic strings are topological defects which can be formed in grand unified theory scale phase transitions in the early universe. They are also predicted to form in the context of string theory. The main mechanism for a network of Nambu-Goto cosmic strings to lose energy is through the production of loops and the subsequent emission of gravitational waves, thus offering an experimental signature for the existence of cosmic strings. Here we report on the analysis conducted to specifically search for gravitational-wave bursts from cosmic string loops in the data of Advanced LIGO 2015-2016 observing run (O1). No evidence of such signals was found in the data, and as a result we set upper limits on the cosmic string parameters for three recent loop distribution models. In this paper, we initially derive constraints on the string tension G μ and the intercommutation probability, using not only the burst analysis performed on the O1 data set but also results from the previously published LIGO stochastic O1 analysis, pulsar timing arrays, cosmic microwave background and big-bang nucleosynthesis experiments. We show that these data sets are complementary in that they probe gravitational waves produced by cosmic string loops during very different epochs. Finally, we show that the data sets exclude large parts of the parameter space of the three loop distribution models we consider.
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“All-sky search for long-duration gravitational wave transients in the first Advanced LIGO observing run”, Classical and Quantum Gravity (2018).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
We present the results of a search for long-duration gravitational wave transients in the data of the LIGO Hanford and LIGO Livingston second generation detectors between September 2015 and January 2016 with, a total observational time of 49d. The search targets gravitational wave transients of 10–500 s duration in a frequency band of 24–2048 Hz, with minimal assumptions about the signal waveform, polarization, source direction, or time of occurrence. No significant events were observed. As a result we set 90% confidence upper limits on the rate of long-duration gravitational wave transients for different types of gravitational wave signals. We also show that the search is sensitive to sources in the Galaxy emitting at least ~10^(−8) M_⊙c^2 in gravitational waves.
2017
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“Upper Limits on the Stochastic Gravitational-Wave Background from Advanced LIGO's First Observing Run”, Physical Review Letters (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
A wide variety of astrophysical and cosmological sources are expected to contribute to a stochastic gravitational-wave background. Following the observations of GW150914 and GW151226, the rate and mass of coalescing binary black holes appear to be greater than many previous expectations. As a result, the stochastic background from unresolved compact binary coalescences is expected to be particularly loud. We perform a search for the isotropic stochastic gravitational-wave background using data from Advanced Laser Interferometer Gravitational Wave Observatory's (a LIGO) first observing run. The data display no evidence of a stochastic gravitational-wave signal. We constrain the dimensionless energy density of gravitational waves to be Ω_0 < 1.7×10^(−7) with 95% confidence, assuming a flat energy density spectrum in the most sensitive part of the LIGO band (20–86 Hz). This is a factor of ∼33 times more sensitive than previous measurements. We also constrain arbitrary power-law spectra. Finally, we investigate the implications of this search for the background of binary black holes using an astrophysical model for the background.
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“Upper Limits on Gravitational Waves from Scorpius X-1 from a Model-based Cross-correlation Search in Advanced LIGO Data”, Astrophysical Journal (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
We present the results of a semicoherent search for continuous gravitational waves from the low-mass X-ray binary Scorpius X-1, using data from the first Advanced LIGO observing run. The search method uses details of the modeled, parametrized continuous signal to combine coherently data separated by less than a specified coherence time, which can be adjusted to trade off sensitivity against computational cost. A search was conducted over the frequency range 25–2000 Hz, spanning the current observationally constrained range of binary orbital parameters. No significant detection candidates were found, and frequency-dependent upper limits were set using a combination of sensitivity estimates and simulated signal injections. The most stringent upper limit was set at 175 Hz, with comparable limits set across the most sensitive frequency range from 100 to 200 Hz. At this frequency, the 95% upper limit on the signal amplitude h0 is 2.3 x 10^(-25) marginalized over the unknown inclination angle of the neutron star's spin, and 8.0 x 10^(-26) assuming the best orientation (which results in circularly polarized gravitational waves). These limits are a factor of 3–4 stronger than those set by other analyses of the same data, and a factor of ~7 stronger than the best upper limits set using data from Initial LIGO science runs. In the vicinity of 100 Hz, the limits are a factor of between 1.2 and 3.5 above the predictions of the torque balance model, depending on the inclination angle; if the most likely inclination angle of 44° is assumed, they are within a factor of 1.7.
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“Towards the Fundamental Quantum Limit of Linear Measurements of Classical Signals”, Physical Review Letters (2017).
Haixing Miao, Rana X. Adhikari, Yiqiu Ma, Belinda Pang, and Yanbei ChenAbstract
The quantum Cramér-Rao bound (QCRB) sets a fundamental limit for the measurement of classical signals with detectors operating in the quantum regime. Using linear-response theory and the Heisenberg uncertainty relation, we derive a general condition for achieving such a fundamental limit. When applied to classical displacement measurements with a test mass, this condition leads to an explicit connection between the QCRB and the standard quantum limit that arises from a tradeoff between the measurement imprecision and quantum backaction; the QCRB can be viewed as an outcome of a quantum nondemolition measurement with the backaction evaded. Additionally, we show that the test mass is more a resource for improving measurement sensitivity than a victim of the quantum backaction, which suggests a new approach to enhancing the sensitivity of a broad class of sensors. We illustrate these points with laser interferometric gravitational-wave detectors.
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“The basic physics of the binary black hole merger GW150914”, Annalen der Physik (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, S. B. Anderson, and K. Arai, et al.Abstract
The first direct gravitational-wave detection was made by the Advanced Laser Interferometer Gravitational Wave Observatory on September 14, 2015. The GW150914 signal was strong enough to be apparent, without using any waveform model, in the filtered detector strain data. Here, features of the signal visible in the data are analyzed using concepts from Newtonian physics and general relativity, accessible to anyone with a general physics background. The simple analysis presented here is consistent with the fully general-relativistic analyses published elsewhere, in showing that the signal was produced by the inspiral and subsequent merger of two black holes. The black holes were each of approximately 35 M⊙, still orbited each other as close as ∼350 km apart and subsequently merged to form a single black hole. Similar reasoning, directly from the data, is used to roughly estimate how far these black holes were from the Earth, and the energy that they radiated in gravitational waves.
Full text · DOI: 10.1002/andp.201600209
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“Search for Post-merger Gravitational Waves from the Remnant of the Binary Neutron Star Merger GW170817”, Astrophysical Journal Letters (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
The first observation of a binary neutron star (NS) coalescence by the Advanced LIGO and Advanced Virgo gravitational-wave (GW) detectors offers an unprecedented opportunity to study matter under the most extreme conditions. After such a merger, a compact remnant is left over whose nature depends primarily on the masses of the inspiraling objects and on the equation of state of nuclear matter. This could be either a black hole (BH) or an NS, with the latter being either long-lived or too massive for stability implying delayed collapse to a BH. Here, we present a search for GWs from the remnant of the binary NS merger GW170817 using data from Advanced LIGO and Advanced Virgo. We search for short- (≾1 s) and intermediate-duration (≾500 s) signals, which include GW emission from a hypermassive NS or supramassive NS, respectively. We find no signal from the post-merger remnant. Our derived strain upper limits are more than an order of magnitude larger than those predicted by most models. For short signals, our best upper limit on the root sum square of the GW strain emitted from 1–4 kHz is h^(50%)_(rss) = 2.1 x 10^(-22) Hz^(-1/2) at 50% detection efficiency. For intermediate-duration signals, our best upper limit at 50% detection efficiency is h^(50%)_(rss) = 8.4 x 10^(-22) Hz^(-1/2) for a millisecond magnetar model, and h^(50%)_(rss) = 5.9 x 10^(-22) Hz^(-1.2) for a bar-mode model. These results indicate that post-merger emission from a similar event may be detectable when advanced detectors reach design sensitivity or with next-generation detectors.
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“Search for intermediate mass black hole binaries in the first observing run of Advanced LIGO”, Physical Review D (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
During their first observational run, the two Advanced LIGO detectors attained an unprecedented sensitivity, resulting in the first direct detections of gravitational-wave signals produced by stellar-mass binary black hole systems. This paper reports on an all-sky search for gravitational waves (GWs) from merging intermediate mass black hole binaries (IMBHBs). The combined results from two independent search techniques were used in this study: the first employs a matched-filter algorithm that uses a bank of filters covering the GW signal parameter space, while the second is a generic search for GW transients (bursts). No GWs from IMBHBs were detected; therefore, we constrain the rate of several classes of IMBHB mergers. The most stringent limit is obtained for black holes of individual mass 100 M⊙, with spins aligned with the binary orbital angular momentum. For such systems, the merger rate is constrained to be less than 0.93 Gpc^(−3) yr^(−1) in comoving units at the 90% confidence level, an improvement of nearly 2 orders of magnitude over previous upper limits.
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“Search for high-energy neutrinos from gravitational wave event GW151226 and candidate LVT151012 with ANTARES and IceCube”, Physical Review D (2017).
A. Albert, B. P. Abbott, R. Abbott, R. X. Adhikari, and A. Ananyeva, et al.Abstract
The Advanced LIGO observatories detected gravitational waves from two binary black hole mergers during their first observation run (O1). We present a high-energy neutrino follow-up search for the second gravitational wave event, GW151226, as well as for gravitational wave candidate LVT151012. We find two and four neutrino candidates detected by IceCube, and one and zero detected by Antares, within ± 500 s around the respective gravitational wave signals, consistent with the expected background rate. None of these neutrino candidates are found to be directionally coincident with GW151226 or LVT151012. We use nondetection to constrain isotropic-equivalent high-energy neutrino emission from GW151226, adopting the GW event's 3D localization, to less than 2 × 10^(51)–2 × 10^(54) erg.
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“Search for High-Energy Neutrinos from Binary Neutron Star Merger GW170817 with ANTARES, Icecube, and the Pierre Auger Observatory”, Astrophysical Journal Letters (2017).
A. Albert, B. P. Abbott, R. Abbott, R. X. Adhikari, and A. Ananyeva, et al.Abstract
The Advanced LIGO and Advanced Virgo observatories recently discovered gravitational waves from a binary neutron star inspiral. A short gamma-ray burst (GRB) that followed the merger of this binary was also recorded by the Fermi Gamma-ray Burst Monitor (Fermi-GBM), and the Anti-Coincidence Shield for the Spectrometer for the International Gamma-Ray Astrophysics Laboratory (INTEGRAL), indicating particle acceleration by the source. The precise location of the event was determined by optical detections of emission following the merger. We searched for high-energy neutrinos from the merger in the GeV–EeV energy range using the Antares, IceCube, and Pierre Auger Observatories. No neutrinos directionally coincident with the source were detected within ±500 s around the merger time. Additionally, no MeV neutrino burst signal was detected coincident with the merger. We further carried out an extended search in the direction of the source for high-energy neutrinos within the 14 day period following the merger, but found no evidence of emission. We used these results to probe dissipation mechanisms in relativistic outflows driven by the binary neutron star merger. The non-detection is consistent with model predictions of short GRBs observed at a large off-axis angle.
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“Search for gravitational waves from Scorpius X-1 in the first Advanced LIGO observing run with a hidden Markov model”, Physical Review D (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
Results are presented from a semicoherent search for continuous gravitational waves from the brightest low-mass X-ray binary, Scorpius X-1, using data collected during the first Advanced LIGO observing run. The search combines a frequency domain matched filter (Bessel-weighted F-statistic) with a hidden Markov model to track wandering of the neutron star spin frequency. No evidence of gravitational waves is found in the frequency range 60–650 Hz. Frequentist 95% confidence strain upper limits, h^(95%)_0 = 4.0 × 10^(−25), 8.3 × 10^(−25), and 3.0 × 10^(−25) for electromagnetically restricted source orientation, unknown polarization, and circular polarization, respectively, are reported at 106 Hz. They are ≤ 10 times higher than the theoretical torque-balance limit at 106 Hz.
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“Search for Gravitational Waves Associated with Gamma-Ray Bursts during the First Advanced LIGO Observing Run and Implications for the Origin of GRB 150906B”, Astrophysical Journal (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
We present the results of the search for gravitational waves (GWs) associated with γ-ray bursts detected during the first observing run of the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO). We find no evidence of a GW signal for any of the 41 γ-ray bursts for which LIGO data are available with sufficient duration. For all γ-ray bursts, we place lower bounds on the distance to the source using the optimistic assumption that GWs with an energy of 10^(-2)M_☉c^2 were emitted within the 16–500 Hz band, and we find a median 90% confidence limit of 71 Mpc at 150 Hz. For the subset of 19 short/hard γ-ray bursts, we place lower bounds on distance with a median 90% confidence limit of 90 Mpc for binary neutron star (BNS) coalescences, and 150 and 139 Mpc for neutron star–black hole coalescences with spins aligned to the orbital angular momentum and in a generic configuration, respectively. These are the highest distance limits ever achieved by GW searches. We also discuss in detail the results of the search for GWs associated with GRB 150906B, an event that was localized by the InterPlanetary Network near the local galaxy NGC 3313, which is at a luminosity distance of 54 Mpc (z = 0.0124). Assuming the γ-ray emission is beamed with a jet half-opening angle ⩽30°, we exclude a BNS and a neutron star–black hole in NGC 3313 as the progenitor of this event with confidence >99%. Further, we exclude such progenitors up to a distance of 102 Mpc and 170 Mpc, respectively.
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“Search for continuous gravitational waves from neutron stars in globular cluster NGC 6544”, Physical Review D (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, S. B. Anderson, and K. Arai, et al.Abstract
We describe a directed search for continuous gravitational waves in data from the sixth initial LIGO science run. The target was the nearby globular cluster NGC 6544 at a distance of ≈2.7 kpc. The search covered a broad band of frequencies along with first and second frequency derivatives for a fixed sky position. The search coherently integrated data from the two LIGO interferometers over a time span of 9.2 days using the matched-filtering F-statistic. We found no gravitational-wave signals and set 95% confidence upper limits as stringent as 6.0×10^(−25) on intrinsic strain and 8.5×10−6 on fiducial ellipticity. These values beat the indirect limits from energy conservation for stars with characteristic spin-down ages older than 300 years and are within the range of theoretical predictions for possible neutron-star ellipticities. An important feature of this search was use of a barycentric resampling algorithm which substantially reduced computational cost; this method is used extensively in searches of Advanced LIGO and Virgo detector data.
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“Quantum correlation measurements in interferometric gravitational-wave detectors”, Physical Review A (2017).
D. V. Martynov, B. P. Abbott, R. Abbott, R. X. Adhikari, and S. B. Anderson, et al.Abstract
Quantum fluctuations in the phase and amplitude quadratures of light set limitations on the sensitivity of modern optical instruments. The sensitivity of the interferometric gravitational-wave detectors, such as the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO), is limited by quantum shot noise, quantum radiation pressure noise, and a set of classical noises. We show how the quantum properties of light can be used to distinguish these noises using correlation techniques. Particularly, in the first part of the paper we show estimations of the coating thermal noise and gas phase noise, hidden below the quantum shot noise in the Advanced LIGO sensitivity curve. We also make projections on the observatory sensitivity during the next science runs. In the second part of the paper we discuss the correlation technique that reveals the quantum radiation pressure noise from the background of classical noises and shot noise. We apply this technique to the Advanced LIGO data, collected during the first science run, and experimentally estimate the quantum correlations and quantum radiation pressure noise in the interferometer.
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“Probing Microplasticity in Small-Scale FCC Crystals via Dynamic Mechanical Analysis”, Physical Review Letters (2017).
Xiaoyue Ni, Stefanos Papanikolaou, Gabriele Vajente, Rana X. Adhikari, and Julia R. GreerAbstract
In small-scale metallic systems, collective dislocation activity has been correlated with size effects in strength and with a steplike plastic response under uniaxial compression and tension. Yielding and plastic flow in these samples is often accompanied by the emergence of multiple dislocation avalanches. Dislocations might be active preyield, but their activity typically cannot be discerned because of the inherent instrumental noise in detecting equipment. We apply alternate current load perturbations via dynamic mechanical analysis during quasistatic uniaxial compression experiments on single crystalline Cu nanopillars with diameters of 500 nm and compute dynamic moduli at frequencies 0.1, 0.3, 1, and 10 Hz under progressively higher static loads until yielding. By tracking the collective aspects of the oscillatory stress-strain-time series in multiple samples, we observe an evolving dissipative component of the dislocation network response that signifies the transition from elastic behavior to dislocation avalanches in the globally preyield regime. We postulate that microplasticity, which is associated with the combination of dislocation avalanches and slow viscoplastic relaxations, is the cause of the dependency of dynamic modulus on the driving rate and the quasistatic stress. We construct a continuum mesoscopic dislocation dynamics model to compute the frequency response of stress over strain and obtain a consistent agreement with experimental observations. The results of our experiments and simulations present a pathway to discern and quantify correlated dislocation activity in the preyield regime of deforming crystals.
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“On the Progenitor of Binary Neutron Star Merger GW170817”, Astrophysical Journal Letters (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
On 2017 August 17 the merger of two compact objects with masses consistent with two neutron stars was discovered through gravitational-wave (GW170817), gamma-ray (GRB 170817A), and optical (SSS17a/AT 2017gfo) observations. The optical source was associated with the early-type galaxy NGC 4993 at a distance of just ~40 Mpc, consistent with the gravitational-wave measurement, and the merger was localized to be at a projected distance of ~2 kpc away from the galaxy's center. We use this minimal set of facts and the mass posteriors of the two neutron stars to derive the first constraints on the progenitor of GW170817 at the time of the second supernova (SN). We generate simulated progenitor populations and follow the three-dimensional kinematic evolution from binary neutron star (BNS) birth to the merger time, accounting for pre-SN galactic motion, for considerably different input distributions of the progenitor mass, pre-SN semimajor axis, and SN-kick velocity. Though not considerably tight, we find these constraints to be comparable to those for Galactic BNS progenitors. The derived constraints are very strongly influenced by the requirement of keeping the binary bound after the second SN and having the merger occur relatively close to the center of the galaxy. These constraints are insensitive to the galaxy's star formation history, provided the stellar populations are older than 1 Gyr.
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“Multi-messenger Observations of a Binary Neutron Star Merger”, Astrophysical Journal Letters (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~ 1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg^2 at a luminosity distance of 40^(+8)_(-8) Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26. M⊙. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient's position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.
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“GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral”, Physical Review Letters (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
On August 17, 2017 at 12∶41:04 UTC the Advanced LIGO and Advanced Virgo gravitational-wave detectors made their first observation of a binary neutron star inspiral. The signal, GW170817, was detected with a combined signal-to-noise ratio of 32.4 and a false-alarm-rate estimate of less than one per 8.0×10^4 years. We infer the component masses of the binary to be between 0.86 and 2.26 M⊙, in agreement with masses of known neutron stars. Restricting the component spins to the range inferred in binary neutron stars, we find the component masses to be in the range 1.17–1.60 M⊙, with the total mass of the system 2.74^(+0.04)_(−0.01)M⊙. The source was localized within a sky region of 28 deg^2(90% probability) and had a luminosity distance of 40^(+8)_(−14) Mpc, the closest and most precisely localized gravitational-wave signal yet. The association with the γ-ray burst GRB 170817A, detected by Fermi-GBM 1.7 s after the coalescence, corroborates the hypothesis of a neutron star merger and provides the first direct evidence of a link between these mergers and short γ-ray bursts. Subsequent identification of transient counterparts across the electromagnetic spectrum in the same location further supports the interpretation of this event as a neutron star merger. This unprecedented joint gravitational and electromagnetic observation provides insight into astrophysics, dense matter, gravitation, and cosmology.
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“GW170814: A three-detector observation of gravitational waves from a binary black hole coalescence”, Physical Review Letters (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
On August 14, 2017 at 10:30:43 UTC, the Advanced Virgo detector and the two Advanced LIGO detectors coherently observed a transient gravitational-wave signal produced by the coalescence of two stellar mass black holes, with a false-alarm-rate of ≾ 1 in 27000 years. The signal was observed with a three-detector network matched-filter signal-to-noise ratio of 18. The inferred masses of the initial black holes are 30.5^(+5.7)_(-3.0)M⊙ and 25.3^(+2.8)_(-4.2)M⊙ (at the 90% credible level). The luminosity distance of the source is 540^(+130)_(-210) Mpc, corresponding to a redshift of z =0.11^(+0.03)_(-0.04). A network of three detectors improves the sky localization of the source, reducing the area of the 90% credible region from 1160 deg^2 using only the two LIGO detectors to 60 deg^2 using all three detectors. For the first time, we can test the nature of gravitational wave polarizations from the antenna response of the LIGO-Virgo network, thus enabling a new class of phenomenological tests of gravity.
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“GW170608: Observation of a 19 Solar-mass Binary Black Hole Coalescence”, Astrophysical Journal Letters (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
On 2017 June 8 at 02:01:16.49 UTC, a gravitational-wave (GW) signal from the merger of two stellar-mass black holes was observed by the two Advanced Laser Interferometer Gravitational-Wave Observatory detectors with a network signal-to-noise ratio of 13. This system is the lightest black hole binary so far observed, with component masses of 12^(+7)_(-2) M⊙ and 7^(+2)_(-2) M⊙ (90% credible intervals). These lie in the range of measured black hole masses in low-mass X-ray binaries, thus allowing us to compare black holes detected through GWs with electromagnetic observations. The source's luminosity distance is 340^(+140)_(-140) Mpc, corresponding to redshift 0.07^(+0.03)_(-0.03). We verify that the signal waveform is consistent with the predictions of general relativity.
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“GW170104: Observation of a 50-Solar-Mass Binary Black Hole Coalescence at Redshift 0.2”, Physical Review Letters (2017).
B. P. Abbott, R. Abbott, C. Adams, R. X. Adhikari, and A. Ananyeva, et al.Abstract
We describe the observation of GW170104, a gravitational-wave signal produced by the coalescence of a pair of stellar-mass black holes. The signal was measured on January 4, 2017 at 10∶11:58.6 UTC by the twin advanced detectors of the Laser Interferometer Gravitational-Wave Observatory during their second observing run, with a network signal-to-noise ratio of 13 and a false alarm rate less than 1 in 70 000 years. The inferred component black hole masses are 31.2^(8.4) _(−6.0)M_⊙ and 19.4^(5.3)_( −5.9)M_⊙ (at the 90% credible level). The black hole spins are best constrained through measurement of the effective inspiral spin parameter, a mass-weighted combination of the spin components perpendicular to the orbital plane, χ_(eff) = −0.12^(0.21)_( −0.30). This result implies that spin configurations with both component spins positively aligned with the orbital angular momentum are disfavored. The source luminosity distance is 880^(450)_(−390) Mpc corresponding to a redshift of z = 0.18^(0.08)_( −0.07) . We constrain the magnitude of modifications to the gravitational-wave dispersion relation and perform null tests of general relativity. Assuming that gravitons are dispersed in vacuum like massive particles, we bound the graviton mass to m_g ≤ 7.7 × 10^(−23) eV/c^2. In all cases, we find that GW170104 is consistent with general relativity.
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“Gravitational Waves and Gamma-Rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A”, Astrophysical Journal Letters (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
On 2017 August 17, the gravitational-wave event GW170817 was observed by the Advanced LIGO and Virgo detectors, and the gamma-ray burst (GRB) GRB 170817A was observed independently by the Fermi Gamma-ray Burst Monitor, and the Anti-Coincidence Shield for the Spectrometer for the International Gamma-Ray Astrophysics Laboratory. The probability of the near-simultaneous temporal and spatial observation of GRB 170817A and GW170817 occurring by chance is 5.0 x 10(-8). We therefore confirm binary neutron star mergers as a progenitor of short GRBs. The association of GW170817 and GRB 170817A provides new insight into fundamental physics and the origin of short GRBs. We use the observed time delay of (+1.74 ± 0.05) s between GRB 170817A and GW170817 to: (i) constrain the difference between the speed of gravity and the speed of light to be between -3 x 10^(-15) and +7 x 10^(-16) times the speed of light, (ii) place new bounds on the violation of Lorentz invariance, (iii) present a new test of the equivalence principle by constraining the Shapiro delay between gravitational and electromagnetic radiation. We also use the time delay to constrain the size and bulk Lorentz factor of the region emitting the gamma-rays. GRB 170817A is the closest short GRB with a known distance, but is between 2 and 6 orders of magnitude less energetic than other bursts with measured redshift. A new generation of gamma-ray detectors, and subthreshold searches in existing detectors, will be essential to detect similar short bursts at greater distances. Finally, we predict a joint detection rate for the Fermi Gamma-ray Burst Monitor and the Advanced LIGO and Virgo detectors of 0.1–1.4 per year during the 2018–2019 observing run and 0.3–1.7 per year at design sensitivity.
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“First Search for Gravitational Waves from Known Pulsars with Advanced LIGO”, Astrophysical Journal (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
A search is performed for Higgs-boson-mediated flavor-changing neutral currents in the decays of top quarks. The search is based on proton-proton collision data corresponding to an integrated luminosity of 19.7 fb^(−1) at a center-of-mass energy of 8 TeV collected with the CMS detector at the LHC. Events in which a top quark pair is produced with one top quark decaying into a charm or up quark and a Higgs boson (H), and the other top quark decaying into a bottom quark and a W boson are selected. The Higgs boson in these events is assumed to subsequently decay into either dibosons or difermions. No significant excess is observed above the expected standard model background, and an upper limit at the 95% confidence level is set on the branching fraction ℬ(t → Hc) of 0.40% and ℬ(t → Hu) of 0.55%, where the expected upper limits are 0.43% and 0.40%, respectively. These results correspond to upper limits on the square of the flavor-changing Higgs boson Yukawa couplings |λ_(tc)H|^2 < 6.9 × 10^(−3) and |λ_(tu)H|^2 < 9.8 × 10^(−3).
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“First narrow-band search for continuous gravitational waves from known pulsars in advanced detector data”, Physical Review D (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
Spinning neutron stars asymmetric with respect to their rotation axis are potential sources of continuous gravitational waves for ground-based interferometric detectors. In the case of known pulsars a fully coherent search, based on matched filtering, which uses the position and rotational parameters obtained from electromagnetic observations, can be carried out. Matched filtering maximizes the signal-to-noise (SNR) ratio, but a large sensitivity loss is expected in case of even a very small mismatch between the assumed and the true signal parameters. For this reason, narrow-band analysis methods have been developed, allowing a fully coherent search for gravitational waves from known pulsars over a fraction of a hertz and several spin-down values. In this paper we describe a narrow-band search of 11 pulsars using data from Advanced LIGO's first observing run. Although we have found several initial outliers, further studies show no significant evidence for the presence of a gravitational wave signal. Finally, we have placed upper limits on the signal strain amplitude lower than the spin-down limit for 5 of the 11 targets over the bands searched; in the case of J1813-1749 the spin-down limit has been beaten for the first time. For an additional 3 targets, the median upper limit across the search bands is below the spin-down limit. This is the most sensitive narrow-band search for continuous gravitational waves carried out so far.
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“First low-frequency Einstein@Home all-sky search for continuous gravitational waves in Advanced LIGO data”, Physical Review D (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
We report results of a deep all-sky search for periodic gravitational waves from isolated neutron stars in data from the first Advanced LIGO observing run. This search investigates the low frequency range of Advanced LIGO data, between 20 and 100 Hz, much of which was not explored in initial LIGO. The search was made possible by the computing power provided by the volunteers of the Einstein@Home project. We find no significant signal candidate and set the most stringent upper limits to date on the amplitude of gravitational wave signals from the target population, corresponding to a sensitivity depth of 48.7 [1/√Hz]. At the frequency of best strain sensitivity, near 100 Hz, we set 90% confidence upper limits of 1.8×10^(−25). At the low end of our frequency range, 20 Hz, we achieve upper limits of 3.9×10^(−24). At 55 Hz we can exclude sources with ellipticities greater than 10^(−5) within 100 pc of Earth with fiducial value of the principal moment of inertia of 10^(38) kg m^2.
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“First Demonstration of Electrostatic Damping of Parametric Instability at Advanced LIGO”, Physical Review Letters (2017).
Carl Blair, Richard Abbott, B. P. Abbott, R. X. Adhikari, and S. B. Anderson, et al.Abstract
Interferometric gravitational wave detectors operate with high optical power in their arms in order to achieve high shot-noise limited strain sensitivity. A significant limitation to increasing the optical power is the phenomenon of three-mode parametric instabilities, in which the laser field in the arm cavities is scattered into higher-order optical modes by acoustic modes of the cavity mirrors. The optical modes can further drive the acoustic modes via radiation pressure, potentially producing an exponential buildup. One proposed technique to stabilize parametric instability is active damping of acoustic modes. We report here the first demonstration of damping a parametrically unstable mode using active feedback forces on the cavity mirror. A 15 538 Hz mode that grew exponentially with a time constant of 182 sec was damped using electrostatic actuation, with a resulting decay time constant of 23 sec. An average control force of 0.03 nN was required to maintain the acoustic mode at its minimum amplitude.
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“Exploring the sensitivity of next generation gravitational wave detectors”, Classical and Quantum Gravity (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, S. B. Anderson, and K. Arai, et al.Abstract
The second-generation of gravitational-wave detectors are just starting operation, and have already yielding their first detections. Research is now concentrated on how to maximize the scientific potential of gravitational-wave astronomy. To support this effort, we present here design targets for a new generation of detectors, which will be capable of observing compact binary sources with high signal-to-noise ratio throughout the Universe.
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“Estimating the contribution of dynamical ejecta in the kilonova associated with GW170817”, Astrophysical Journal Letters (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
The source of the gravitational-wave (GW) signal GW170817, very likely a binary neutron star merger, was also observed electromagnetically, providing the first multi-messenger observations of this type. The two-week-long electromagnetic (EM) counterpart had a signature indicative of an r-process-induced optical transient known as a kilonova. This Letter examines how the mass of the dynamical ejecta can be estimated without a direct electromagnetic observation of the kilonova, using GW measurements and a phenomenological model calibrated to numerical simulations of mergers with dynamical ejecta. Specifically, we apply the model to the binary masses inferred from the GW measurements, and use the resulting mass of the dynamical ejecta to estimate its contribution (without the effects of wind ejecta) to the corresponding kilonova light curves from various models. The distributions of dynamical ejecta mass range between M_(ej) = 10^(-3) – 10^(-2) M⊙ for various equations of state, assuming that the neutron stars are rotating slowly. In addition, we use our estimates of the dynamical ejecta mass and the neutron star merger rates inferred from GW170817 to constrain the contribution of events like this to the r-process element abundance in the Galaxy when ejecta mass from post-merger winds is neglected. We find that if ≳10% of the matter dynamically ejected from binary neutron star (BNS) mergers is converted to r-process elements, GW170817-like BNS mergers could fully account for the amount of r-process material observed in the Milky Way.
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“Effects of waveform model systematics on the interpretation of GW150914”, Classical and Quantum Gravity (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
Parameter estimates of GW150914 were obtained using Bayesian inference, based on three semi-analytic waveform models for binary black hole coalescences. These waveform models differ from each other in their treatment of black hole spins, and all three models make some simplifying assumptions, notably to neglect sub-dominant waveform harmonic modes and orbital eccentricity. Furthermore, while the models are calibrated to agree with waveforms obtained by full numerical solutions of Einstein's equations, any such calibration is accurate only to some non-zero tolerance and is limited by the accuracy of the underlying phenomenology, availability, quality, and parameter-space coverage of numerical simulations. This paper complements the original analyses of GW150914 with an investigation of the effects of possible systematic errors in the waveform models on estimates of its source parameters. To test for systematic errors we repeat the original Bayesian analysis on mock signals from numerical simulations of a series of binary configurations with parameters similar to those found for GW150914. Overall, we find no evidence for a systematic bias relative to the statistical error of the original parameter recovery of GW150914 due to modeling approximations or modeling inaccuracies. However, parameter biases are found to occur for some configurations disfavored by the data of GW150914: for binaries inclined edge-on to the detector over a small range of choices of polarization angles, and also for eccentricities greater than ~0.05. For signals with higher signal-to-noise ratio than GW150914, or in other regions of the binary parameter space (lower masses, larger mass ratios, or higher spins), we expect that systematic errors in current waveform models may impact gravitational-wave measurements, making more accurate models desirable for future observations.
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“Effects of transients in LIGO suspensions on searches for gravitational waves”, Review of Scientific Instruments (2017).
M. Walker, J. McIver, B. P. Abbott, R. Abbott, and R. X. Adhikari, et al.Abstract
This paper presents an analysis of the transient behavior of the Advanced LIGO (Laser Interferometer Gravitational-wave Observatory) suspensions used to seismically isolate the optics. We have characterized the transients in the longitudinal motion of the quadruple suspensions during Advanced LIGO's first observing run. Propagation of transients between stages is consistent with modeled transfer functions, such that transient motion originating at the top of the suspension chain is significantly reduced in amplitude at the test mass. We find that there are transients seen by the longitudinal motion monitors of quadruple suspensions, but they are not significantly correlated with transient motion above the noise floor in the gravitational wave strain data, and therefore do not present a dominant source of background noise in the searches for transient gravitational wave signals. Using the suspension transfer functions, we compared the transients in a week of gravitational wave strain data with transients from a quadruple suspension. Of the strain transients between 10 and 60 Hz, 84% are loud enough that they would have appeared above the sensor noise in the top stage quadruple suspension monitors if they had originated at that stage at the same frequencies. We find no significant temporal correlation with the suspension transients in that stage, so we can rule out suspension motion originating at the top stage as the cause of those transients. However, only 3.2% of the gravitational wave strain transients are loud enough that they would have been seen by the second stage suspension sensors, and none of them are above the sensor noise levels of the penultimate stage. Therefore, we cannot eliminate the possibility of transient noise in the detectors originating in the intermediate stages of the suspension below the sensing noise.
Full text · DOI: 10.1063/1.5000264
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“Directional Limits on Persistent Gravitational Waves from Advanced LIGO's First Observing Run”, Physical Review Letters (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
We employ gravitational-wave radiometry to map the stochastic gravitational wave background expected from a variety of contributing mechanisms and test the assumption of isotropy using data from the Advanced Laser Interferometer Gravitational Wave Observatory's (aLIGO) first observing run. We also search for persistent gravitational waves from point sources with only minimal assumptions over the 20–1726 Hz frequency band. Finding no evidence of gravitational waves from either point sources or a stochastic background, we set limits at 90% confidence. For broadband point sources, we report upper limits on the gravitational wave energy flux per unit frequency in the range F_(α,Θ)(f)<(0.1–56)×10^(-8) erg cm^(-2) s^(-1) Hz^(-1)(f/25 Hz)^(α-1) depending on the sky location Θ and the spectral power index α. For extended sources, we report upper limits on the fractional gravitational wave energy density required to close the Universe of Ω(f,Θ)<(0.39–7.6)×10^(-8) sr-^(-1)(f/25 Hz)α depending on Θ and α. Directed searches for narrowband gravitational waves from astrophysically interesting objects (Scorpius X-1, Supernova 1987 A, and the Galactic Center) yield median frequency-dependent limits on strain amplitude of h_0<(6.7,5.5, and 7.0)×10^(-25), respectively, at the most sensitive detector frequencies between 130–175 Hz. This represents a mean improvement of a factor of 2 across the band compared to previous searches of this kind for these sky locations, considering the different quantities of strain constrained in each case.
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“Cryogenically cooled ultra low vibration silicon mirrors for gravitational wave observatories”, Cryogenics (2017).
Brett Shapiro, Rana X. Adhikari, Odylio Aguiar, Edgard Bonilla, Danyang Fan, Litawn Gan, Ian Gomez, Sanditi Khandelwal, Brian Lantz, Tim MacDonald, and Dakota Madden-FongAbstract
Interferometric gravitational wave observatories recently launched a new field of gravitational wave astronomy with the first detections of gravitational waves in 2015. The number and quality of these detections is limited in part by thermally induced vibrations in the mirrors, which show up as noise in these interferometers. One way to reduce this thermally induced noise is to use low temperature mirrors made of high purity single-crystalline silicon. However, these low temperatures must be achieved without increasing the mechanical vibration of the mirror surface or the vibration of any surface within close proximity to the mirrors. The vibration of either surface can impose a noise inducing phase shift on the light within the interferometer or physically push the mirror through oscillating radiation pressure. This paper proposes a system for the Laser Interferometric Gravitational-wave Observatory (LIGO) to achieve the dual goals of low temperature and low vibration to reduce the thermally induced noise in silicon mirrors. Experimental results are obtained at Stanford University to prove that these dual goals can be realized simultaneously.
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“Calibration of the Advanced LIGO detectors for the discovery of the binary black-hole merger GW150914”, Physical Review D (2017).
B. P. Abbott, R. Abbott, M. R. Abernathy, R. X. Adhikari, and S. B. Anderson, et al.Abstract
In Advanced LIGO, detection and astrophysical source parameter estimation of the binary black hole merger GW150914 requires a calibrated estimate of the gravitational-wave strain sensed by the detectors. Producing an estimate from each detector's differential arm length control loop readout signals requires applying time domain filters, which are designed from a frequency domain model of the detector's gravitational-wave response. The gravitational-wave response model is determined by the detector's opto-mechanical response and the properties of its feedback control system. The measurements used to validate the model and characterize its uncertainty are derived primarily from a dedicated photon radiation pressure actuator, with cross-checks provided by optical and radio frequency references. We describe how the gravitational-wave readout signal is calibrated into equivalent gravitational-wave-induced strain and how the statistical uncertainties and systematic errors are assessed. Detector data collected over 38 calendar days, from September 12 to October 20, 2015, contain the event GW150914 and approximately 16 days of coincident data used to estimate the event false alarm probability. The calibration uncertainty is less than 10% in magnitude and 10° in phase across the relevant frequency band, 20 Hz to 1 kHz.
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“All-sky search for short gravitational-wave bursts in the first Advanced LIGO run”, Physical Review D (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
We present the results from an all-sky search for short-duration gravitational waves in the data of the first run of the Advanced LIGO detectors between September 2015 and January 2016. The search algorithms use minimal assumptions on the signal morphology, so they are sensitive to a wide range of sources emitting gravitational waves. The analyses target transient signals with duration ranging from milliseconds to seconds over the frequency band of 32 to 4096 Hz. The first observed gravitational-wave event, GW150914, has been detected with high confidence in this search; the other known gravitational-wave event, GW151226, falls below the search's sensitivity. Besides GW150914, all of the search results are consistent with the expected rate of accidental noise coincidences. Finally, we estimate rate-density limits for a broad range of non-binary-black-hole transient gravitational-wave sources as a function of their gravitational radiation emission energy and their characteristic frequency. These rate-density upper limits are stricter than those previously published by an order of magnitude.
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“All-sky search for periodic gravitational waves in the O1 LIGO data”, Physical Review D (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
We report on an all-sky search for periodic gravitational waves in the frequency band 20–475 Hz and with a frequency time derivative in the range of [−1.0,+0.1] × 10^(−8) Hz/s. Such a signal could be produced by a nearby spinning and slightly nonaxisymmetric isolated neutron star in our galaxy. This search uses the data from Advanced LIGO's first observational run, O1. No periodic gravitational wave signals were observed, and upper limits were placed on their strengths. The lowest upper limits on worst-case (linearly polarized) strain amplitude h_0 are ∼4 × 10^(−25) near 170 Hz. For a circularly polarized source (most favorable orientation), the smallest upper limits obtained are ∼1.5 × 10^(−25). These upper limits refer to all sky locations and the entire range of frequency derivative values. For a population-averaged ensemble of sky locations and stellar orientations, the lowest upper limits obtained for the strain amplitude are ~2.5 × 10^(−25).
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“A gravitational-wave standard siren measurement of the Hubble constant”, Nature (2017).
B. P. Abbott, R. Abbott, R. X. Adhikari, A. Ananyeva, and S. B. Anderson, et al.Abstract
On 17 August 2017, the Advanced LIGO and Virgo detectors observed the gravitational-wave event GW170817—a strong signal from the merger of a binary neutron-star system. Less than two seconds after the merger, a γ-ray burst (GRB 170817A) was detected within a region of the sky consistent with the LIGO–Virgo-derived location of the gravitational-wave source. This sky region was subsequently observed by optical astronomy facilities, resulting in the identification of an optical transient signal within about ten arcseconds of the galaxy NGC 4993. This detection of GW170817 in both gravitational waves and electromagnetic waves represents the first 'multi-messenger' astronomical observation. Such observations enable GW170817 to be used as a 'standard siren' (meaning that the absolute distance to the source can be determined directly from the gravitational-wave measurements) to measure the Hubble constant. This quantity represents the local expansion rate of the Universe, sets the overall scale of the Universe and is of fundamental importance to cosmology. Here we report a measurement of the Hubble constant that combines the distance to the source inferred purely from the gravitational-wave signal with the recession velocity inferred from measurements of the redshift using the electromagnetic data. In contrast to previous measurements, ours does not require the use of a cosmic 'distance ladder': the gravitational-wave analysis can be used to estimate the luminosity distance out to cosmological scales directly, without the use of intermediate astronomical distance measurements. We determine the Hubble constant to be about 70 kilometres per second per megaparsec. This value is consistent with existing measurements, while being completely independent of them. Additional standard siren measurements from future gravitational-wave sources will enable the Hubble constant to be constrained to high precision.
Full text · DOI: 10.1038/nature24471
2016
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“Upper Limits on the Rates of Binary Neutron Star and Neutron-Star—Black-Hole Mergers from Advanced Ligo's First Observing Run”, Astrophysical Journal Letters (2016).
B. P. Abbott, R. Abbott, R. X. Adhikari, S. B. Anderson, and K. Arai, et al.Abstract
We report here the non-detection of gravitational waves from the merger of binary neutron star systems and neutron-star–black-hole systems during the first observing run of Advanced LIGO. In particular we searched for gravitational wave signals from binary neutron star systems with component masses ∈ [1,3] M_⊙ and component dimensionless spins < 0.05. We also searched for neutron-star–black-hole systems with the same neutron star parameters, black hole mass ∈ [2,99] M_⊙ and no restriction on the black hole spin magnitude. We assess the sensitivity of the two LIGO detectors to these systems, and find that they could have detected the merger of binary neutron star systems with component mass distributions of 1.35 ± 0.13M_⊙ at a volume-weighted average distance of ~ 70 Mpc, and for neutron-star–black-hole systems with neutron star masses of 1.4M_⊙ and black hole masses of at least 5M_⊙, a volume-weighted average distance of at least ~ 110 Mpc. From this we constrain with 90% confidence the merger rate to be less than 12,600 Gpc^(-3) yr^(-1) for binary-neutron star systems and less than 3,600 Gpc^(-3) yr^(-1) for neutron-star–black-hole systems. We discuss the astrophysical implications of these results, which we find to be in tension with only the most optimistic predictions. However, we find that if no detection of neutron-star binary mergers is made in the next two Advanced LIGO and Advanced Virgo observing runs we would place significant constraints on the merger rates. Finally, assuming a rate of 10^(+20)_(-7) Gpc^(-3) yr^(-1) short gamma ray bursts beamed towards the Earth and assuming that all short gamma ray bursts have binary-neutron-star (neutron-star–black-hole) progenitors we can use our 90% confidence rate upper limits to constrain the beaming angle of the gamma-ray burst to be greater than 2.3^(+1.7º)_(-1.1) (4.3^(+3.1º)_(-1.9)).
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“Towards a first design of a Newtonian-noise cancellation system for Advanced LIGO”, Classical and Quantum Gravity (2016).
M. Coughlin, N. Mukund, J. Harms, J. Driggers, R. Adhikari, and S. MitraAbstract
Newtonian gravitational noise from seismic fields is predicted to be a limiting noise source at low frequency for second generation gravitational-wave detectors. Mitigation of this noise will be achieved by Wiener filtering using arrays of seismometers deployed in the vicinity of all test masses. In this work, we present optimized configurations of seismometer arrays using a variety of simplified models of the seismic field based on seismic observations at LIGO Hanford. The model that best fits the seismic measurements leads to noise reduction limited predominantly by seismometer self-noise. A first simplified design of seismic arrays for Newtonian-noise cancellation at the LIGO sites is presented, which suggests that it will be sufficient to monitor surface displacement inside the buildings.
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“The Rate of Binary Black Hole Mergers Inferred from Advanced LIGO Observations Surrounding GW150914”, Astrophysical Journal Letters (2016).
B. P. Abbott, R. Abbott, M. R. Abernathy, R. X. Adhikari, and S. B. Anderson, et al.Abstract
A transient gravitational-wave signal, GW150914, was identified in the twin Advanced LIGO detectors on September 14, 2015 at 09:50:45 UTC. To assess the implications of this discovery, the detectors remained in operation with unchanged configurations over a period of 39 d around the time of the signal. At the detection statistic threshold corresponding to that observed for GW150914, our search of the 16 days of simultaneous two-detector observational data is estimated to have a false alarm rate (FAR) of < 4.9 × 10^(−6) yr^(−1), yielding a p-value for GW150914 of < 2 × 10^(−7). Parameter estimation followup on this trigger identifies its source as a binary black hole (BBH) merger with component masses (m_1, m_2) = (36^(+5)_(−4), 29^(+4)_(−4)) M_⊙ at redshift z = 0.09^(+0.03)_(−0.04) (median and 90\% credible range). Here we report on the constraints these observations place on the rate of BBH coalescences. Considering only GW150914, assuming that all BBHs in the Universe have the same masses and spins as this event, imposing a search FAR threshold of 1 per 100 years, and assuming that the BBH merger rate is constant in the comoving frame, we infer a 90% credible range of merger rates between 2--53 Gpc^(−3) yr^(−1) (comoving frame). Incorporating all search triggers that pass a much lower threshold while accounting for the uncertainty in the astrophysical origin of each trigger, we estimate a higher rate, ranging from 13--600 Gpc^(−3) yr^(−1) depending on assumptions about the BBH mass distribution. All together, our various rate estimates fall in the conservative range 2--600 Gpc^(−3) yr^(−1).
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“Tests of General Relativity with GW150914”, Physical Review Letters (2016).
B. P. Abbott, R. Abbott, M. R. Abernathy, R. X. Adhikari, and S. B. Anderson, et al.Abstract
The LIGO detection of GW150914 provides an unprecedented opportunity to study the two-body motion of a compact-object binary in the large-velocity, highly nonlinear regime, and to witness the final merger of the binary and the excitation of uniquely relativistic modes of the gravitational field. We carry out several investigations to determine whether GW150914 is consistent with a binary black-hole merger in general relativity. We find that the final remnant's mass and spin, as determined from the low-frequency (inspiral) and high-frequency (postinspiral) phases of the signal, are mutually consistent with the binary black-hole solution in general relativity. Furthermore, the data following the peak of GW150914 are consistent with the least-damped quasinormal mode inferred from the mass and spin of the remnant black hole. By using waveform models that allow for parametrized general-relativity violations during the inspiral and merger phases, we perform quantitative tests on the gravitational-wave phase in the dynamical regime and we determine the first empirical bounds on several high-order post-Newtonian coefficients. We constrain the graviton Compton wavelength, assuming that gravitons are dispersed in vacuum in the same way as particles with mass, obtaining a 90%-confidence lower bound of 10^(13 ) km. In conclusion, within our statistical uncertainties, we find no evidence for violations of general relativity in the genuinely strong-field regime of gravity.
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“Supplement: The Rate of Binary Black Hole Mergers Inferred from Advanced LIGO Observations Surrounding GW150914”, Astrophysical Journal Supplement Series (2016).
B. P. Abbott, M. R. Abernathy, R. X. Adhikari, S. B. Anderson, and K. Arai, et al.Abstract
This article provides supplemental information for a Letter reporting the rate of (BBH) coalescences inferred from 16 days of coincident Advanced LIGO observations surrounding the transient (GW) signal GW150914. In that work we reported various rate estimates whose 90% confidence intervals fell in the range 2–600 Gpc^(−3) yr^(−1). Here we give details on our method and computations, including information about our search pipelines, a derivation of our likelihood function for the analysis, a description of the astrophysical search trigger distribution expected from merging BBHs, details on our computational methods, a description of the effects and our model for calibration uncertainty, and an analytic method for estimating our detector sensitivity, which is calibrated to our measurements.
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“Sensitivity of the Advanced LIGO detectors at the beginning of gravitational wave astronomy”, Physical Review D (2016).
D. V. Martynov, E. D. Hall, B. P. Abbott, R. Abbott, and R. X. Adhikari, et al.Abstract
The Laser Interferometer Gravitational Wave Observatory (LIGO) consists of two widely separated 4 km laser interferometers designed to detect gravitational waves from distant astrophysical sources in the frequency range from 10 Hz to 10 kHz. The first observation run of the Advanced LIGO detectors started in September 2015 and ended in January 2016. A strain sensitivity of better than 10^(−23)/√Hz was achieved around 100 Hz. Understanding both the fundamental and the technical noise sources was critical for increasing the astrophysical strain sensitivity. The average distance at which coalescing binary black hole systems with individual masses of 30 M⊙ could be detected above a signal-to-noise ratio (SNR) of 8 was 1.3 Gpc, and the range for binary neutron star inspirals was about 75 Mpc. With respect to the initial detectors, the observable volume of the Universe increased by a factor 69 and 43, respectively. These improvements helped Advanced LIGO to detect the gravitational wave signal from the binary black hole coalescence, known as GW150914.
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“Search of the Orion spur for continuous gravitational waves using a loosely coherent algorithm on data from LIGO interferometers”, Physical Review D (2016).
J. Aasi, B. P. Abbott, R. Abbott, M. R. Abernathy, and R. X. Adhikari, et al.Abstract
We report results of a wideband search for periodic gravitational waves from isolated neutron stars within the Orion spur towards both the inner and outer regions of our Galaxy. As gravitational waves interact very weakly with matter, the search is unimpeded by dust and concentrations of stars. One search disk (A) is 6.87° in diameter and centered on 20^h10^m54.71^s+33°33′25.29′′, and the other (B) is 7.45° in diameter and centered on 8^h35^m20.61^s−46°49′25.151′′. We explored the frequency range of 50–1500 Hz and frequency derivative from 0 to −5×10^(−9) Hz/s. A multistage, loosely coherent search program allowed probing more deeply than before in these two regions, while increasing coherence length with every stage. Rigorous follow-up parameters have winnowed the initial coincidence set to only 70 candidates, to be examined manually. None of those 70 candidates proved to be consistent with an isolated gravitational-wave emitter, and 95% confidence level upper limits were placed on continuous-wave strain amplitudes. Near 169 Hz we achieve our lowest 95% C.L. upper limit on the worst-case linearly polarized strain amplitude h_0 of 6.3×10^(−25), while at the high end of our frequency range we achieve a worst-case upper limit of 3.4×10^(−24) for all polarizations and sky locations.
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“Search for transient gravitational waves in coincidence with short-duration radio transients during 2007-2013”, Physical Review D (2016).
B. P. Abbott, R. Abbott, M. R. Abernathy, Rana X. Adhikari, and S. B. Anderson, et al.Abstract
We present an archival search for transient gravitational-wave bursts in coincidence with 27 single-pulse triggers from Green Bank Telescope pulsar surveys, using the LIGO, Virgo, and GEO interferometer network. We also discuss a check for gravitational-wave signals in coincidence with Parkes fast radio bursts using similar methods. Data analyzed in these searches were collected between 2007 and 2013. Possible sources of emission of both short-duration radio signals and transient gravitational-wave emission include starquakes on neutron stars, binary coalescence of neutron stars, and cosmic string cusps. While no evidence for gravitational-wave emission in coincidence with these radio transients was found, the current analysis serves as a prototype for similar future searches using more sensitive second-generation interferometers.
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“Results of the deepest all-sky survey for continuous gravitational waves on LIGO S6 data running on the Einstein@Home volunteer distributed computing project”, Physical Review D (2016).
B. P. Abbott, R. Abbott, R. X. Adhikari, S. B. Anderson, and K. Arai, et al.Abstract
We report results of a deep all-sky search for periodic gravitational waves from isolated neutron stars in data from the S6 LIGO science run. The search was possible thanks to the computing power provided by the volunteers of the Einstein@Home distributed computing project. We find no significant signal candidate and set the most stringent upper limits to date on the amplitude of gravitational wave signals from the target population. At the frequency of best strain sensitivity, between 170.5 and 171 Hz we set a 90% confidence upper limit of 5.5×10^(−25), while at the high end of our frequency range, around 505 Hz, we achieve upper limits ≃10^(−24). At 230 Hz we can exclude sources with ellipticities greater than 10^(−6) within 100 pc of Earth with fiducial value of the principal moment of inertia of 10 38 kg m^2. If we assume a higher (lower) gravitational wave spin-down we constrain farther (closer) objects to higher (lower) ellipticities.
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“Prospects for Observing and Localizing Gravitational-Wave Transients with Advanced LIGO and Advanced Virgo”, Living Reviews in Relativity (2016).
B. P. Abbott, R. Abbott, M. R. Abernathy, R. X. Adhikari, and S. B. Anderson, et al.Abstract
We present a possible observing scenario for the Advanced LIGO and Advanced Virgo gravitational-wave detectors over the next decade, with the intention of providing information to the astronomy community to facilitate planning for multi-messenger astronomy with gravitational waves. We determine the expected sensitivity of the network to transient gravitational-wave signals, and study the capability of the network to determine the sky location of the source. We report our findings for gravitational-wave transients, with particular focus on gravitational-wave signals from the inspiral of binary neutron-star systems, which are considered the most promising for multi-messenger astronomy. The ability to localize the sources of the detected signals depends on the geographical distribution of the detectors and their relative sensitivity, and 90% credible regions can be as large as thousands of square degrees when only two sensitive detectors are operational. Determining the sky position of a significant fraction of detected signals to areas of 5 deg^2 to 20 deg^2 will require at least three detectors of sensitivity within a factor of ∼ 2 of each other and with a broad frequency bandwidth. Should the third LIGO detector be relocated to India as expected, a significant fraction of gravitational-wave signals will be localized to a few square degrees by gravitational-wave observations alone.
Full text · DOI: 10.1007/lrr-2016-1
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“Properties of the Binary Black Hole Merger GW150914”, Physical Review Letters (2016).
B. P. Abbott, R. Abbott, M. R. Abernathy, R. X. Adhikari, and S. B. Anderson, et al.Abstract
On September 14, 2015, the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected a gravitational-wave transient (GW150914); we characterize the properties of the source and its parameters. The data around the time of the event were analyzed coherently across the LIGO network using a suite of accurate waveform models that describe gravitational waves from a compact binary system in general relativity. GW150914 was produced by a nearly equal mass binary black hole of masses 36^(+5)_(−4)M_⊙ and 29^(+4)_(−4)M_⊙; for each parameter we report the median value and the range of the 90% credible interval. The dimensionless spin magnitude of the more massive black hole is bound to be <0.7 (at 90% probability). The luminosity distance to the source is 410^(+160)_(−180) Mpc, corresponding to a redshift 0.09+0.03−0.04 assuming standard cosmology. The source location is constrained to an annulus section of 610 deg^2, primarily in the southern hemisphere. The binary merges into a black hole of mass 62^(+4)_(−4)M_⊙ and spin 0.67^(+0.05)_(−0.07). This black hole is significantly more massive than any other inferred from electromagnetic observations in the stellar-mass regime.
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“Passive, free-space heterodyne laser gyroscope”, Classical and Quantum Gravity (2016).
W. Z. Korth, A. Heptonstall, E. D. Hall, K. Arai, E. K. Gustafson, and R. X. AdhikariAbstract
Laser gyroscopes making use of the Sagnac effect have been used as highly accurate rotation sensors for many years. First used in aerospace and defense applications, these devices have more recently been used for precision seismology and in other research settings. In particular, mid-sized (~1 m-scale) laser gyros have been under development as tilt sensors to augment the adaptive active seismic isolation systems in terrestrial interferometric gravitational wave detectors. The most prevalent design is the 'active' gyroscope, in which the optical ring cavity used to measure the Sagnac degeneracy breaking is itself a laser resonator. In this article, we describe another topology: a 'passive' gyroscope, in which the sensing cavity is not itself a laser but is instead tracked using external laser beams. While subject to its own limitations, this design is free from the deleterious lock-in effects observed in active systems, and has the advantage that it can be constructed using commercially available components. We demonstrate that our device achieves comparable sensitivity to those of similarly sized active laser gyroscopes.
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“Observing gravitational-wave transient GW150914 with minimal assumptions”, Physical Review D (2016).
B. P. Abbott, R. Abbott, M. R. Abernathy, R. X. Adhikari, and S. B. Anderson, et al.Abstract
The gravitational-wave signal GW150914 was first identified on September 14, 2015, by searches for short-duration gravitational-wave transients. These searches identify time-correlated transients in multiple detectors with minimal assumptions about the signal morphology, allowing them to be sensitive to gravitational waves emitted by a wide range of sources including binary black hole mergers. Over the observational period from September 12 to October 20, 2015, these transient searches were sensitive to binary black hole mergers similar to GW150914 to an average distance of ∼600 Mpc. In this paper, we describe the analyses that first detected GW150914 as well as the parameter estimation and waveform reconstruction techniques that initially identified GW150914 as the merger of two black holes. We find that the reconstructed waveform is consistent with the signal from a binary black hole merger with a chirp mass of ∼30 M_⊙ and a total mass before merger of ∼70 M_⊙ in the detector frame.
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“Observation of Gravitational Waves from a Binary Black Hole Merger”, Physical Review Letters (2016).
K. S. Thorne, R. W. P. Drever, R. X. Adhikari, Y. Chen, and C. D. Ott, et al.Abstract
On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10^(−21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203 000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410 +160/−180 Mpc corresponding to a redshift z=0.09 +0.03/−0.04. In the source frame, the initial black hole masses are 36+5−4M_⊙ and 29+4−4M_⊙, and the final black hole mass is 62+4−4M⊙, with 3.0+0.5−0.5M_⊙c^2 radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.
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“Measurement of mechanical loss in the Acktar Black coating of silicon wafers”, Classical and Quantum Gravity (2016).
M. R. Abernathy, N. Smith, W. Z. Korth, R. X. Adhikari, L. G Prokhorov, D. V. Koptsov, and V. P. MitrofanovAbstract
Some proposed interferometric gravitational wave detectors of the next generation are designed to use silicon test masses cooled to cryogenic temperatures. The test masses will need to be partially coated with high emissivity coating to provide sufficient cooling when they absorb the laser light. The mechanical loss of the Acktar Black coating is determined based on the measurements of the Q-factors of the bending vibration modes of coated and uncoated commercial silicon wafers. The Young's modulus of the coating material is determined using nanoindentation. We use this information to calculate thermal noise of the silicon test masses associated with a high emissivity coating on its lateral side (barrel). It is found that such a coating results in a less than 9% increase of the total strain noise of LIGO Voyager design for a future cryogenic gravitational wave detector.
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“Localization and Broadband Follow-up of the Gravitational-wave Transient GW150914”, Astrophysical Journal Letters (2016).
B. P. Abbott, R. Abbott, M. R. Abernathy, R. X. Adhikari, and S. B. Anderson, et al.Abstract
A gravitational-wave (GW) transient was identified in data recorded by the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) detectors on 2015 September 14. The event, initially designated G184098 and later given the name GW150914, is described in detail elsewhere. By prior arrangement, preliminary estimates of the time, significance, and sky location of the event were shared with 63 teams of observers covering radio, optical, near-infrared, X-ray, and gamma-ray wavelengths with ground- and space-based facilities. In this Letter we describe the low-latency analysis of the GW data and present the sky localization of the first observed compact binary merger. We summarize the follow-up observations reported by 25 teams via private Gamma-ray Coordinates Network circulars, giving an overview of the participating facilities, the GW sky localization coverage, the timeline, and depth of the observations. As this event turned out to be a binary black hole merger, there is little expectation of a detectable electromagnetic (EM) signature. Nevertheless, this first broadband campaign to search for a counterpart of an Advanced LIGO source represents a milestone and highlights the broad capabilities of the transient astronomy community and the observing strategies that have been developed to pursue neutron star binary merger events. Detailed investigations of the EM data and results of the EM follow-up campaign are being disseminated in papers by the individual teams.
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“Improved analysis of GW150914 using a fully spin-precessing waveform model”, Physical Review X (2016).
B. P. Abbott, R. Abbott, R. X. Adhikari, S. B. Anderson, and K. Arai, et al.Abstract
This paper presents updated estimates of source parameters for GW150914, a binary black-hole coalescence event detected by the Laser Interferometer Gravitational-wave Observatory (LIGO) in 2015 [Abbott et al. Phys. Rev. Lett. 116, 061102 (2016).]. Abbott et al. [Phys. Rev. Lett. 116, 241102 (2016).] presented parameter estimation of the source using a 13-dimensional, phenomenological precessing-spin model (precessing IMRPhenom) and an 11-dimensional nonprecessing effective-one-body (EOB) model calibrated to numerical-relativity simulations, which forces spin alignment (nonprecessing EOBNR). Here, we present new results that include a 15-dimensional precessing-spin waveform model (precessing EOBNR) developed within the EOB formalism. We find good agreement with the parameters estimated previously [Abbott et al. Phys. Rev. Lett. 116, 241102 (2016).], and we quote updated component masses of 35^(+5)_(−3) M⊙ and 30^(+3)_(−4) M⊙ (where errors correspond to 90% symmetric credible intervals). We also present slightly tighter constraints on the dimensionless spin magnitudes of the two black holes, with a primary spin estimate <0.65 and a secondary spin estimate <0.75 at 90% probability. Abbott et al. [Phys. Rev. Lett. 116, 241102 (2016).] estimated the systematic parameter-extraction errors due to waveform-model uncertainty by combining the posterior probability densities of precessing IMRPhenom and nonprecessing EOBNR. Here, we find that the two precessing-spin models are in closer agreement, suggesting that these systematic errors are smaller than previously quoted.
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“High-energy Neutrino follow-up search of Gravitational Wave Event GW150914 with ANTARES and IceCube”, Physical Review D (2016).
S. Adrián-Martínez, B. P. Abbott, R. Abbott, M. R. Abernathy, and R. X. Adhikari, et al.Abstract
We present the high-energy-neutrino follow-up observations of the first gravitational wave transient GW150914 observed by the Advanced LIGO detectors on September 14, 2015. We search for coincident neutrino candidates within the data recorded by the IceCube and Antares neutrino detectors. A possible joint detection could be used in targeted electromagnetic follow-up observations, given the significantly better angular resolution of neutrino events compared to gravitational waves. We find no neutrino candidates in both temporal and spatial coincidence with the gravitational wave event. Within ±500 s of the gravitational wave event, the number of neutrino candidates detected by IceCube and Antares were three and zero, respectively. This is consistent with the expected atmospheric background, and none of the neutrino candidates were directionally coincident with GW150914. We use this nondetection to constrain neutrino emission from the gravitational-wave event.
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“High power and ultra-low-noise photodetector for squeezed-light enhanced gravitational wave detectors”, Optics Express (2016).
Hartmut Grote, Michael Weinert, Rana X. Adhikari, Christoph Affeldt, Volker Kringel, Jonathan Leong, James Lough, Harald Lück, Emil Schreiber, Kenneth A. Strain, Henning Vahlbruch, and Holger WittelAbstract
Current laser-interferometric gravitational wave detectors employ a self-homodyne readout scheme where a comparatively large light power (5–50 mW) is detected per photosensitive element. For best sensitivity to gravitational waves, signal levels as low as the quantum shot noise have to be measured as accurately as possible. The electronic noise of the detection circuit can produce a relevant limit to this accuracy, in particular when squeezed states of light are used to reduce the quantum noise. We present a new electronic circuit design reducing the electronic noise of the photodetection circuit in the audio band. In the application of this circuit at the gravitational-wave detector GEO 600 the shot-noise to electronic noise ratio was permanently improved by a factor of more than 4 above 1 kHz, while the dynamic range was improved by a factor of 7. The noise equivalent photocurrent of the implemented photodetector and circuit is about 5 µA/√Hz above 1 kHz with a maximum detectable photocurrent of 20 mA. With the new circuit, the observed squeezing level in GEO 600 increased by 0.2 dB. The new circuit also creates headroom for higher laser power and more squeezing to be observed in the future in GEO 600 and is applicable to other optics experiments.
Full text · DOI: 10.1364/oe.24.020107
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“GW151226: Observation of Gravitational Waves from a 22-Solar-Mass Binary Black Hole Coalescence”, Physical Review Letters (2016).
B. P. Abbott, R. Abbott, R. X. Adhikari, S. B. Anderson, and K. Arai, et al.Abstract
We report the observation of a gravitational-wave signal produced by the coalescence of two stellar-mass black holes. The signal, GW151226, was observed by the twin detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) on December 26, 2015 at 03:38:53 UTC. The signal was initially identified within 70 s by an online matched-filter search targeting binary coalescences. Subsequent off-line analyses recovered GW151226 with a network signal-to-noise ratio of 13 and a significance greater than 5σ. The signal persisted in the LIGO frequency band for approximately 1 s, increasing in frequency and amplitude over about 55 cycles from 35 to 450 Hz, and reached a peak gravitational strain of 3.4^(+0.7)_(-0.9) ×10^(-22). The inferred source-frame initial black hole masses are 14.2^(+8.3)_(-3.7) M⊙ and 7.5^(+2.3)_(-2.3) M⊙, and the final black hole mass is 20.8^(+6.1)_(-1.7) M⊙. We find that at least one of the component black holes has spin greater than 0.2. This source is located at a luminosity distance of 440^(+180)_(-190) Mpc corresponding to a redshift of 0.09^(+0.03)_(-0.04). All uncertainties define a 90% credible interval. This second gravitational-wave observation provides improved constraints on stellar populations and on deviations from general relativity.
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“GW150914: The Advanced LIGO Detectors in the Era of First Discoveries”, Physical Review Letters (2016).
B. P. Abbott, R. Abbott, M. R. Abernathy, R. X. Adhikari, and S. B. Anderson, et al.Abstract
Following a major upgrade, the two advanced detectors of the Laser Interferometer Gravitational-wave Observatory (LIGO) held their first observation run between September 2015 and January 2016. With a strain sensitivity of 10^(−23)/√Hz at 100 Hz, the product of observable volume and measurement time exceeded that of all previous runs within the first 16 days of coincident observation. On September 14, 2015, the Advanced LIGO detectors observed a transient gravitational-wave signal determined to be the coalescence of two black holes [B. P. Abbott et al., Phys. Rev. Lett. 116, 061102 (2016)], launching the era of gravitational-wave astronomy. The event, GW150914, was observed with a combined signal-to-noise ratio of 24 in coincidence by the two detectors. Here, we present the main features of the detectors that enabled this observation. At full sensitivity, the Advanced LIGO detectors are designed to deliver another factor of 3 improvement in the signal-to-noise ratio for binary black hole systems similar in mass to GW150914.
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“GW150914: Implications for the Stochastic Gravitational-Wave Background from Binary Black Holes”, Physical Review Letters (2016).
B. P. Abbott, R. Abbott, M. R. Abernathy, R. X. Adhikari, and S. B. Anderson, et al.Abstract
The LIGO detection of the gravitational wave transient GW150914, from the inspiral and merger of two black holes with masses ≳30M_⊙, suggests a population of binary black holes with relatively high mass. This observation implies that the stochastic gravitational-wave background from binary black holes, created from the incoherent superposition of all the merging binaries in the Universe, could be higher than previously expected. Using the properties of GW150914, we estimate the energy density of such a background from binary black holes. In the most sensitive part of the Advanced LIGO and Advanced Virgo band for stochastic backgrounds (near 25 Hz), we predict Ω_(GW)(f=25 Hz)=1.1^(+2.7)_(−0.9)×10^−9 with 90% confidence. This prediction is robustly demonstrated for a variety of formation scenarios with different parameters. The differences between models are small compared to the statistical uncertainty arising from the currently poorly constrained local coalescence rate. We conclude that this background is potentially measurable by the Advanced LIGO and Advanced Virgo detectors operating at their projected final sensitivity.
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“GW150914: First results from the search for binary black hole coalescence with Advanced LIGO”, Physical Review D (2016).
B. P. Abbott, R. Abbott, M. R. Abernathy, R. X. Adhikari, and S. B. Anderson, et al.Abstract
On September 14, 2015, at 09∶50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) simultaneously observed the binary black hole merger GW150914. We report the results of a matched-filter search using relativistic models of compact-object binaries that recovered GW150914 as the most significant event during the coincident observations between the two LIGO detectors from September 12 to October 20, 2015 GW150914 was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203000 years, equivalent to a significance greater than 5.1 σ.
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“First low frequency all-sky search for continuous gravitational wave signals”, Physical Review D (2016).
J. Aasi, R. Abbott, T. D. Abbott, M. R. Abernathy, and R. X. Adhikari, et al.Abstract
In this paper we present the results of the first low frequency all-sky search of continuous gravitational wave signals conducted on Virgo VSR2 and VSR4 data. The search covered the full sky, a frequency range between 20 Hz and 128 Hz with a range of spin-down between −1.0×10^(−10) Hz/s and +1.5×10^(−11) Hz/s, and was based on a hierarchical approach. The starting point was a set of short Fast Fourier Transforms (FFT), of length 8192 seconds, built from the calibrated strain data. Aggressive data cleaning, both in the time and frequency domains, has been done in order to remove, as much as possible, the effect of disturbances of instrumental origin. On each dataset a number of candidates has been selected, using the FrequencyHough transform in an incoherent step. Only coincident candidates among VSR2 and VSR4 have been examined in order to strongly reduce the false alarm probability, and the most significant candidates have been selected. The criteria we have used for candidate selection and for the coincidence step greatly reduce the harmful effect of large instrumental artifacts. Selected candidates have been subject to a follow-up by constructing a new set of longer FFTs followed by a further incoherent analysis. No evidence for continuous gravitational wave signals was found, therefore we have set a population-based joint VSR2-VSR4 90% confidence level upper limit on the dimensionless gravitational wave strain in the frequency range between 20 Hz and 128 Hz. This is the first all-sky search for continuous gravitational waves conducted at frequencies below 50 Hz. We set upper limits in the range between about 10^(−24) and 2×10^(−23) at most frequencies. Our upper limits on signal strain show an improvement of up to a factor of ∼2 with respect to the results of previous all-sky searches at frequencies below 80 Hz.
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“Directly comparing GW150914 with numerical solutions of Einstein's equations for binary black hole coalescence”, Physical Review D (2016).
B. P. Abbott, R. Abbott, R. X. Adhikari, S. B. Anderson, and W. G. Anderson, et al.Abstract
We compare GW150914 directly to simulations of coalescing binary black holes in full general relativity, including several performed specifically to reproduce this event. Our calculations go beyond existing semianalytic models, because for all simulations—including sources with two independent, precessing spins—we perform comparisons which account for all the spin-weighted quadrupolar modes, and separately which account for all the quadrupolar and octopolar modes. Consistent with the posterior distributions reported by Abbott et al. [Phys. Rev. Lett. 116, 241102 (2016)] (at the 90% credible level), we find the data are compatible with a wide range of nonprecessing and precessing simulations. Follow-up simulations performed using previously estimated binary parameters most resemble the data, even when all quadrupolar and octopolar modes are included. Comparisons including only the quadrupolar modes constrain the total redshifted mass M_z ∈[64 M_⊙−82 M_⊙], mass ratio 1/q = m_2/m_1 ∈[0.6,1], and effective aligned spin χ_(eff) ∈[−0.3,0.2], where χ_(eff)=(S_1/m_1+S_2/m_2)⋅L/M. Including both quadrupolar and octopolar modes, we find the mass ratio is even more tightly constrained. Even accounting for precession, simulations with extreme mass ratios and effective spins are highly inconsistent with the data, at any mass. Several nonprecessing and precessing simulations with similar mass ratio and χ_(eff) are consistent with the data. Though correlated, the components' spins (both in magnitude and directions) are not significantly constrained by the data: the data is consistent with simulations with component spin magnitudes ɑ_(1,2) up to at least 0.8, with random orientations. Further detailed follow-up calculations are needed to determine if the data contain a weak imprint from transverse (precessing) spins. For nonprecessing binaries, interpolating between simulations, we reconstruct a posterior distribution consistent with previous results. The final black hole's redshifted mass is consistent with Mf,z in the range 64.0 M_⊙−73.5 M_⊙ and the final black hole's dimensionless spin parameter is consistent with ɑ_f = 0.62–0.73. As our approach invokes no intermediate approximations to general relativity and can strongly reject binaries whose radiation is inconsistent with the data, our analysis provides a valuable complement to Abbott et al. [Phys. Rev. Lett. 116, 241102 (2016)].
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“Comprehensive all-sky search for periodic gravitational waves in the sixth science run LIGO data”, Physical Review D (2016).
B. P. Abbott, R. Abbott, R. X. Adhikari, S. B. Anderson, and K. Arai, et al.Abstract
We report on a comprehensive all-sky search for periodic gravitational waves in the frequency band 100–1500 Hz and with a frequency time derivative in the range of [−1.18,+1.00]×10^(−8) Hz/s. Such a signal could be produced by a nearby spinning and slightly nonaxisymmetric isolated neutron star in our galaxy. This search uses the data from the initial LIGO sixth science run and covers a larger parameter space with respect to any past search. A Loosely Coherent detection pipeline was applied to follow up weak outliers in both Gaussian (95% recovery rate) and non-Gaussian (75% recovery rate) bands. No gravitational wave signals were observed, and upper limits were placed on their strength. Our smallest upper limit on worst-case (linearly polarized) strain amplitude h_0 is 9.7×10^(−25) near 169 Hz, while at the high end of our frequency range we achieve a worst-case upper limit of 5.5×10^(−24). Both cases refer to all sky locations and entire range of frequency derivative values.
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“Coherent Cancellation of Photothermal Noise in GaAs/Al_(0.92)Ga_(0.08)As Bragg Mirrors”, Metrologia (2016).
Tara Chalermsongsak, Evan D. Hall, Garrett D. Cole, David Follman, Frank Seifert, Koji Arai, Eric K. Gustafson, Joshua R. Smith, Markus Aspelmeyer, and Rana X. AdhikariAbstract
Thermal noise is a limiting factor in many high-precision optical experiments. A search is underway for novel optical materials with reduced thermal noise. One such pair of materials, gallium arsenide and aluminum-alloyed gallium arsenide (collectively referred to as AlGaAs), shows promise for its low Brownian noise when compared to conventional materials such as silica and tantala. However, AlGaAs has the potential to produce a high level of thermo-optic noise. We have fabricated a set of AlGaAs crystalline coatings, transferred to fused silica substrates, whose layer structure has been optimized to reduce thermo-optic noise by inducing coherent cancellation of the thermoelastic and thermorefractive effects. By measuring the photothermal transfer function of these mirrors, we find evidence that this optimization has been successful.
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“Characterization of transient noise in Advanced LIGO relevant to gravitational wave signal GW150914”, Classical and Quantum Gravity (2016).
B. P. Abbott, R. Abbott, M. R. Abernathy, R. X. Adhikari, and S. B. Anderson, et al.Abstract
On 14 September 2015, a gravitational wave signal from a coalescing black hole binary system was observed by the Advanced LIGO detectors. This paper describes the transient noise backgrounds used to determine the significance of the event (designated GW150914) and presents the results of investigations into potential correlated or uncorrelated sources of transient noise in the detectors around the time of the event. The detectors were operating nominally at the time of GW150914. We have ruled out environmental influences and non-Gaussian instrument noise at either LIGO detector as the cause of the observed gravitational wave signal.
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“Binary Black Hole Mergers in the First Advanced LIGO Observing Run”, Physical Review X (2016).
B. P. Abbott, R. Abbott, R. X. Adhikari, S. B. Anderson, and K. Arai, et al.Abstract
The first observational run of the Advanced LIGO detectors, from September 12, 2015 to January 19, 2016, saw the first detections of gravitational waves from binary black hole mergers. In this paper, we present full results from a search for binary black hole merger signals with total masses up to 100M⊙ and detailed implications from our observations of these systems. Our search, based on general-relativistic models of gravitational-wave signals from binary black hole systems, unambiguously identified two signals, GW150914 and GW151226, with a significance of greater than 5σ over the observing period. It also identified a third possible signal, LVT151012, with substantially lower significance and with an 87% probability of being of astrophysical origin. We provide detailed estimates of the parameters of the observed systems. Both GW150914 and GW151226 provide an unprecedented opportunity to study the two-body motion of a compact-object binary in the large velocity, highly nonlinear regime. We do not observe any deviations from general relativity, and we place improved empirical bounds on several high-order post-Newtonian coefficients. From our observations, we infer stellar-mass binary black hole merger rates lying in the range 9–240 Gpc^(−3) yr^(−1). These observations are beginning to inform astrophysical predictions of binary black hole formation rates and indicate that future observing runs of the Advanced detector network will yield many more gravitational-wave detections.
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“Astrophysical Implications of the Binary Black Hole Merger GW150914”, Astrophysical Journal Letters (2016).
B. P. Abbott, R. Abbott, M. R. Abernathy, R. X. Adhikari, and S. B. Anderson, et al.Abstract
The discovery of the gravitational-wave (GW) source GW150914 with the Advanced LIGO detectors provides the first observational evidence for the existence of binary black hole (BH) systems that inspiral and merge within the age of the universe. Such BH mergers have been predicted in two main types of formation models, involving isolated binaries in galactic fields or dynamical interactions in young and old dense stellar environments. The measured masses robustly demonstrate that relatively "heavy" BHs (≳25 M_☉) can form in nature. This discovery implies relatively weak massive-star winds and thus the formation of GW150914 in an environment with a metallicity lower than about 1/2 of the solar value. The rate of binary-BH (BBH) mergers inferred from the observation of GW150914 is consistent with the higher end of rate predictions (≳1 Gpc^(−3) yr^(−1)) from both types of formation models. The low measured redshift (z ≃ 0.1) of GW150914 and the low inferred metallicity of the stellar progenitor imply either BBH formation in a low-mass galaxy in the local universe and a prompt merger, or formation at high redshift with a time delay between formation and merger of several Gyr. This discovery motivates further studies of binary-BH formation astrophysics. It also has implications for future detections and studies by Advanced LIGO and Advanced Virgo, and GW detectors in space.
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“An instrument to measure mechanical up-conversion phenomena in metals in the elastic regime”, Review of Scientific Instruments (2016).
G. Vajente, E. A. Quintero, X. Ni, K. Arai, E. K. Gustafson, N. A. Robertson, E. J. Sanchez, J. R. Greer, and R. X. AdhikariAbstract
Crystalline materials, such as metals, are known to exhibit deviation from a simple linear relation between strain and stress when the latter exceeds the yield stress. In addition, it has been shown that metals respond to varying external stress in a discontinuous way in this regime, exhibiting discrete releases of energy. This crackling noise has been extensively studied both experimentally and theoretically when the metals are operating in the plastic regime. In our study, we focus on the behavior of metals in the elastic regime, where the stresses are well below the yield stress. We describe an instrument that aims to characterize non-linear mechanical noise in metals when stressed in the elastic regime. In macroscopic systems, this phenomenon is expected to manifest as a non-stationary noise modulated by external disturbances applied to the material, a form of mechanical up-conversion of noise. The main motivation for this work is for the case of maraging steel components (cantilevers and wires) in the suspension systems of terrestrial gravitational wave detectors. Such instruments are planned to reach very ambitious displacement sensitivities, and therefore mechanical noise in the cantilevers could prove to be a limiting factor for the detectors' final sensitivities, mainly due to non-linear up-conversion of low frequency residual seismic motion to the frequencies of interest for the gravitational wave observations. We describe here the experimental setup, with a target sensitivity of 10^(−15) m/√Hz in the frequency range of 10–1000 Hz, a simple phenomenological model of the non-linear mechanical noise, and the analysis method that is inspired by this model.
Full text · DOI: 10.1063/1.4953114
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“All-sky search for long-duration gravitational wave transients with initial LIGO”, Physical Review D (2016).
B. P. Abbott, R. Abbott, M. R. Abernathy, R. X. Adhikari, and S. B. Anderson, et al.Abstract
We present the results of a search for long-duration gravitational wave transients in two sets of data collected by the LIGO Hanford and LIGO Livingston detectors between November 5, 2005 and September 30, 2007, and July 7, 2009 and October 20, 2010, with a total observational time of 283.0 days and 132.9 days, respectively. The search targets gravitational wave transients of duration 10–500 s in a frequency band of 40–1000 Hz, with minimal assumptions about the signal waveform, polarization, source direction, or time of occurrence. All candidate triggers were consistent with the expected background; as a result we set 90% confidence upper limits on the rate of long-duration gravitational wave transients for different types of gravitational wave signals. For signals from black hole accretion disk instabilities, we set upper limits on the source rate density between 3.4×10^(−5) and 9.4×10^(−4) Mpc^(−3) yr^(−1) at 90% confidence. These are the first results from an all-sky search for unmodeled long-duration transient gravitational waves.
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“A First Targeted Search for Gravitational-Wave Bursts from Core-Collapse Supernovae in Data of First-Generation Laser Interferometer Detectors”, Physical Review D (2016).
B. P. Abbott, R. Abbott, M. R. Abernathy, R. X. Adhikari, and S. B. Anderson, et al.Abstract
We present results from a search for gravitational-wave bursts coincident with two core-collapse supernovae observed optically in 2007 and 2011. We employ data from the Laser Interferometer Gravitational-wave Observatory (LIGO), the Virgo gravitational-wave observatory, and the GEO 600 gravitational-wave observatory. The targeted core-collapse supernovae were selected on the basis of (1) proximity (within approximately 15 Mpc), (2) tightness of observational constraints on the time of core collapse that defines the gravitational-wave search window, and (3) coincident operation of at least two interferometers at the time of core collapse.We find no plausible gravitational-wave candidates. We present the probability of detecting signals from both astrophysically well-motivated and more speculative gravitational-wave emission mechanisms as a function of distance from Earth, and discuss the implications for the detection of gravitational waves from core-collapse supernovae by the upgraded Advanced LIGO and Virgo detectors.
2015
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“Towards the Laboratory Search for Space-Time Dissipation”, (2015).
Huan Yang, Larry R. Price, Nicholas D. Smith, Rana X. Adhikari, Haixing Miao, and Yanbei ChenAbstract
It has been speculated that gravity could be an emergent phenomenon, with classical general relativity as an effective, macroscopic theory, valid only for classical systems at large temporal and spatial scales. As in classical continuum dynamics, the existence of underlying microscopic degrees of freedom may lead to macroscopic dissipative behaviors. With the hope that such dissipative behaviors of gravity could be revealed by carefully designed experiments in the laboratory, we consider a phenomenological model that adds dissipations to the gravitational field, much similar to frictions in solids and fluids. Constraints to such dissipative behavior can already be imposed by astrophysical observations and existing experiments, but mostly in lower frequencies. We propose a series of experiments working in higher frequency regimes, which may potentially put more stringent bounds on these models.
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“Searching for stochastic gravitational waves using data from the two colocated LIGO Hanford detectors”, Physical Review D (2015).
J. Aasi, J. Abadie, B. P. Abbott, R. Abbott, and T. Abbott, et al.Abstract
Searches for a stochastic gravitational-wave background (SGWB) using terrestrial detectors typically involve cross-correlating data from pairs of detectors. The sensitivity of such cross-correlation analyses depends, among other things, on the separation between the two detectors: the smaller the separation, the better the sensitivity. Hence, a colocated detector pair is more sensitive to a gravitational-wave background than a noncolocated detector pair. However, colocated detectors are also expected to suffer from correlated noise from instrumental and environmental effects that could contaminate the measurement of the background. Hence, methods to identify and mitigate the effects of correlated noise are necessary to achieve the potential increase in sensitivity of colocated detectors. Here we report on the first SGWB analysis using the two LIGO Hanford detectors and address the complications arising from correlated environmental noise. We apply correlated noise identification and mitigation techniques to data taken by the two LIGO Hanford detectors, H1 and H2, during LIGO's fifth science run. At low frequencies, 40–460 Hz, we are unable to sufficiently mitigate the correlated noise to a level where we may confidently measure or bound the stochastic gravitational-wave signal. However, at high frequencies, 460–1000 Hz, these techniques are sufficient to set a 95% confidence level upper limit on the gravitational-wave energy density of Ω(f)<7.7×10^(−4)(f/900 Hz)^3, which improves on the previous upper limit by a factor of ∼180. In doing so, we demonstrate techniques that will be useful for future searches using advanced detectors, where correlated noise (e.g., from global magnetic fields) may affect even widely separated detectors.
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“Searches for Continuous Gravitational Waves from Nine Young Supernova Remnants”, Astrophysical Journal (2015).
J. Aasi, B. P. Abbott, R. Abbott, M. R. Abernathy, and R. X. Adhikari, et al.Abstract
We describe directed searches for continuous gravitational waves (GWs) in data from the sixth Laser Interferometer Gravitational-wave Observatory (LIGO) science data run. The targets were nine young supernova remnants not associated with pulsars; eight of the remnants are associated with non-pulsing suspected neutron stars. One target's parameters are uncertain enough to warrant two searches, for a total of 10. Each search covered a broad band of frequencies and first and second frequency derivatives for a fixed sky direction. The searches coherently integrated data from the two LIGO interferometers over time spans from 5.3–25.3 days using the matched-filtering F-statistic. We found no evidence of GW signals. We set 95% confidence upper limits as strong (low) as 4 × 10^(−25) on intrinsic strain, 2 × 10^(−7) on fiducial ellipticity, and 4 × 10^(−5) on r-mode amplitude. These beat the indirect limits from energy conservation and are within the range of theoretical predictions for neutron-star ellipticities and r-mode amplitudes.
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“Observation of Parametric Instability in Advanced LIGO”, Physical Review Letters (2015).
Matthew Evans, Denis Martynov, Aidan Brooks, Dennis Coyne, Richard Abbott, Rana X. Adhikari, Koji Arai, Rolf Bork, Bill Kells, Jameson Rollins, Nicolas Smith-Lefebvre, Gabriele Vajente, and Hiroaki YamamotoAbstract
Parametric instabilities have long been studied as a potentially limiting effect in high-power interferometric gravitational wave detectors. Until now, however, these instabilities have never been observed in a kilometer-scale interferometer. In this Letter, we describe the first observation of parametric instability in a gravitational wave detector, and the means by which it has been removed as a barrier to progress.
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“Noise and control decoupling of Advanced LIGO suspensions”, Classical and Quantum Gravity (2015).
B. N. Shapiro, R. Adhikari, J. Driggers, J. Kissel, B. Lantz, J. Rollins, and K. Youcef-ToumiAbstract
Ground-based interferometric gravitational wave observatories such as Advanced LIGO must isolate their optics from ground vibrations with suspension systems to meet their stringent noise requirements. These suspensions typically have very high quality-factor resonances that require active damping. The sensor noise associated with this damping is a potential significant contributor to the sensitivity of these interferometers. This paper introduces a novel scheme for suspension damping that isolates much of this noise and permits greater amounts of damping. It also decouples the damping feedback design from the interferometer control. The scheme works by invoking a change from a local coordinate frame associated with each suspension, to a coordinate frame aligned with the interferometric readout. In this way, degrees of freedom invisible to the readout can employ effective, but noisy damping. The degree of freedom measured by the readout is then damped using low noise interferometer signals, eliminating the need to use the usual noisy sensors. Simulated and experimental results validate the concepts presented in this paper.
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“Narrow-band search of continuous gravitational-wave signals from Crab and Vela pulsars in Virgo VSR4 data”, Physical Review D (2015).
J. Aasi, B. P. Abbott, R. Abbott, M. R. Abernathy, and R. X. Adhikari, et al.Abstract
In this paper we present the results of a coherent narrow-band search for continuous gravitational-wave signals from the Crab and Vela pulsars conducted on Virgo VSR4 data. In order to take into account a possible small mismatch between the gravitational-wave frequency and two times the star rotation frequency, inferred from measurement of the electromagnetic pulse rate, a range of 0.02 Hz around two times the star rotational frequency has been searched for both the pulsars. No evidence for a signal has been found and 95% confidence level upper limits have been computed assuming both that polarization parameters are completely unknown and that they are known with some uncertainty, as derived from x-ray observations of the pulsar wind torii. For Vela the upper limits are comparable to the spin-down limit, computed assuming that all the observed spin-down is due to the emission of gravitational waves. For Crab the upper limits are about a factor of 2 below the spin-down limit, and represent a significant improvement with respect to past analysis. This is the first time the spin-down limit is significantly overcome in a narrow-band search.
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“In situcharacterization of the thermal state of resonant optical interferometers via tracking of their higher-order mode resonances”, Classical and Quantum Gravity (2015).
Chris L. Mueller, Paul Fulda, Rana X. Adhikari, Koji Arai, Aidan F. Brooks, Rijuparna Chakraborty, Valery V. Frolov, Peter Fritschel, Eleanor J. King, David B. Tanner, Hiroaki Yamamoto, and Guido MuellerAbstract
Thermal lensing in resonant optical interferometers such as those used for gravitational wave detection is a concern due to the negative impact on control signals and instrument sensitivity. In this paper we describe a method for monitoring the thermal state of such interferometers by probing the higher-order spatial mode resonances of the cavities within them. We demonstrate the use of this technique to measure changes in the advanced LIGO (aLIGO) input mode cleaner cavity geometry as a function of input power, and subsequently infer the optical absorption at the mirror surfaces at the level of 1 ppm per mirror. We also demonstrate the generation of a useful error signal for the thermal state of the aLIGO power recycling cavity by continuously tracking the first order spatial mode resonance frequency. Such an error signal could be used as an input to thermal compensation systems to maintain the interferometer cavity geometries in the presence of transients in circulating light power levels, thereby maintaining optimal sensitivity and maximizing the duty-cycle of the detectors.
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“Directed search for gravitational waves from Scorpius X-1 with initial LIGO data”, Physical Review D (2015).
J. Aasi, B. P. Abbott, R. Abbott, M. R. Abernathy, and R. X. Adhikari, et al.Abstract
We present results of a search for continuously emitted gravitational radiation, directed at the brightest low-mass x-ray binary, Scorpius X-1. Our semicoherent analysis covers 10 days of LIGO S5 data ranging from 50–550 Hz, and performs an incoherent sum of coherent F-statistic power distributed amongst frequency-modulated orbital sidebands. All candidates not removed at the veto stage were found to be consistent with noise at a 1% false alarm rate. We present Bayesian 95% confidence upper limits on gravitational-wave strain amplitude using two different prior distributions: a standard one, with no a priori assumptions about the orientation of Scorpius X-1; and an angle-restricted one, using a prior derived from electromagnetic observations. Median strain upper limits of 1.3×10^(−24) and 8×10^(−25) are reported at 150 Hz for the standard and angle-restricted searches respectively. This proof-of-principle analysis was limited to a short observation time by unknown effects of accretion on the intrinsic spin frequency of the neutron star, but improves upon previous upper limits by factors of ∼1.4 for the standard, and 2.3 for the angle-restricted search at the sensitive region of the detector.
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“Characterization of the LIGO detectors during their sixth science run”, Classical and Quantum Gravity (2015).
J. Aasi, J. Abadie, B. P. Abbott, R. Abbott, and M. R. Abernathy, et al.Abstract
In 2009–2010, the Laser Interferometer Gravitational-Wave Observatory (LIGO) operated together with international partners Virgo and GEO600 as a network to search for gravitational waves (GWs) of astrophysical origin. The sensitivity of these detectors was limited by a combination of noise sources inherent to the instrumental design and its environment, often localized in time or frequency, that couple into the GW readout. Here we review the performance of the LIGO instruments during this epoch, the work done to characterize the detectors and their data, and the effect that transient and continuous noise artefacts have on the sensitivity of LIGO to a variety of astrophysical sources.
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“Broadband measurement of coating thermal noise in rigid Fabry–Pérot cavities”, Metrologia (2015).
Tara Chalermsongsak, Frank Seifert, Evan D. Hall, Koji Arai, Eric K. Gustafson, and Rana X. AdhikariAbstract
We report on the relative length fluctuation of two fixed-spacer Fabry–Pérot cavities with mirrors fabricated from silica/tantala dielectric coatings on fused silica substrates. By locking a laser to each cavity and reading out the beat note v = v_1− v_2 of the transmitted beams, we find that, for frequencies from 10 Hz to 1 kHz, the power spectral density of beat note fluctuation is S_v(f)=(0.5Hz)^2/f. By careful budgeting of noise sources contributing to the beat note, we find that our measurement is consistent with the fluctuation in this band being dominated by the Brownian noise of the mirror coatings. Fitting for the coating loss angle ⌽_c, we find it equal to 4 × 10^(−4). We then use a Bayesian analysis to combine our measurement with previous observations, and thereby extract estimates for the individual loss angles of the silica and tantala constituents of these coatings. With minor upgrades, the testbed described in this article can be used in the future to measure the length noise of cavities formed with novel mirror coating materials and geometries.
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“Advanced LIGO”, Classical and Quantum Gravity (2015).
J. Aasi, B. P. Abbott, R. Abbott, M. R. Abernathy, and R. X. Adhikari, et al.Abstract
The Advanced LIGO gravitational wave detectors are second-generation instruments designed and built for the two LIGO observatories in Hanford, WA and Livingston, LA, USA. The two instruments are identical in design, and are specialized versions of a Michelson interferometer with 4 km long arms. As in Initial LIGO, Fabry–Perot cavities are used in the arms to increase the interaction time with a gravitational wave, and power recycling is used to increase the effective laser power. Signal recycling has been added in Advanced LIGO to improve the frequency response. In the most sensitive frequency region around 100 Hz, the design strain sensitivity is a factor of 10 better than Initial LIGO. In addition, the low frequency end of the sensitivity band is moved from 40 Hz down to 10 Hz. All interferometer components have been replaced with improved technologies to achieve this sensitivity gain. Much better seismic isolation and test mass suspensions are responsible for the gains at lower frequencies. Higher laser power, larger test masses and improved mirror coatings lead to the improved sensitivity at mid and high frequencies. Data collecting runs with these new instruments are planned to begin in mid-2015.
2014
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“The NINJA-2 project: detecting and characterizing gravitational waveforms modelled using numerical binary black hole simulations”, Classical and Quantum Gravity (2014).
J. Aasi, B. P. Abbott, R. Abbott, M. R. Abernathy, and Rana X. Adhikari, et al.Abstract
The Numerical INJection Analysis (NINJA) project is a collaborative effort between members of the numerical relativity and gravitational-wave (GW) astrophysics communities. The purpose of NINJA is to study the ability to detect GWs emitted from merging binary black holes (BBH) and recover their parameters with next-generation GW observatories. We report here on the results of the second NINJA project, NINJA-2, which employs 60 complete BBH hybrid waveforms consisting of a numerical portion modelling the late inspiral, merger, and ringdown stitched to a post-Newtonian portion modelling the early inspiral. In a 'blind injection challenge' similar to that conducted in recent Laser Interferometer Gravitational Wave Observatory (LIGO) and Virgo science runs, we added seven hybrid waveforms to two months of data recoloured to predictions of Advanced LIGO (aLIGO) and Advanced Virgo (AdV) sensitivity curves during their first observing runs. The resulting data was analysed by GW detection algorithms and 6 of the waveforms were recovered with false alarm rates smaller than 1 in a thousand years. Parameter-estimation algorithms were run on each of these waveforms to explore the ability to constrain the masses, component angular momenta and sky position of these waveforms. We find that the strong degeneracy between the mass ratio and the BHs' angular momenta will make it difficult to precisely estimate these parameters with aLIGO and AdV. We also perform a large-scale Monte Carlo study to assess the ability to recover each of the 60 hybrid waveforms with early aLIGO and AdV sensitivity curves. Our results predict that early aLIGO and AdV will have a volume-weighted average sensitive distance of 300 Mpc (1 Gpc) for 10M_⊙ + 10M_⊙ (50M_⊙ + 50M_⊙) BBH coalescences. We demonstrate that neglecting the component angular momenta in the waveform models used in matched-filtering will result in a reduction in sensitivity for systems with large component angular momenta. This reduction is estimated to be up to ~15% for 50M_⊙ + 50M_⊙ BBH coalescences with almost maximal angular momenta aligned with the orbit when using early aLIGO and AdV sensitivity curves.
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“Search for Gravitational Waves Associated with γ-ray Bursts Detected by the Interplanetary Network”, Physical Review Letters (2014).
J. Aasi, B. P. Abbott, R. Abbott, M. R. Abernathy, and R. X. Adhikari, et al.Abstract
We present the results of a search for gravitational waves associated with 223 γ-ray bursts (GRBs) detected by the InterPlanetary Network (IPN) in 2005–2010 during LIGO's fifth and sixth science runs and Virgo's first, second, and third science runs. The IPN satellites provide accurate times of the bursts and sky localizations that vary significantly from degree scale to hundreds of square degrees. We search for both a well-modeled binary coalescence signal, the favored progenitor model for short GRBs, and for generic, unmodeled gravitational wave bursts. Both searches use the event time and sky localization to improve the gravitational wave search sensitivity as compared to corresponding all-time, all-sky searches. We find no evidence of a gravitational wave signal associated with any of the IPN GRBs in the sample, nor do we find evidence for a population of weak gravitational wave signals associated with the GRBs. For all IPN-detected GRBs, for which a sufficient duration of quality gravitational wave data are available, we place lower bounds on the distance to the source in accordance with an optimistic assumption of gravitational wave emission energy of 10^(−2)M⊙c^2 at 150 Hz, and find a median of 13 Mpc. For the 27 short-hard GRBs we place 90% confidence exclusion distances to two source models: a binary neutron star coalescence, with a median distance of 12 Mpc, or the coalescence of a neutron star and black hole, with a median distance of 22 Mpc. Finally, we combine this search with previously published results to provide a population statement for GRB searches in first-generation LIGO and Virgo gravitational wave detectors and a resulting examination of prospects for the advanced gravitational wave detectors.
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“Search for gravitational wave ringdowns from perturbed intermediate mass black holes in LIGO-Virgo data from 2005–2010”, Physical Review D (2014).
J. Aasi, B. P. Abbott, R. Abbott, D. L. Abernathy, and R. X. Adhikari, et al.Abstract
We report results from a search for gravitational waves produced by perturbed intermediate mass black holes (IMBH) in data collected by LIGO and Virgo between 2005 and 2010. The search was sensitive to astrophysical sources that produced damped sinusoid gravitational wave signals, also known as ringdowns, with frequency 50≤f_0/Hz≤2000 and decay timescale 0.0001≲τ/s≲0.1 characteristic of those produced in mergers of IMBH pairs. No significant gravitational wave candidate was detected. We report upper limits on the astrophysical coalescence rates of IMBHs with total binary mass 50≤M/M_⊙≤450 and component mass ratios of either 1:1 or 4:1. For systems with total mass 100≤M/M_⊙≤150, we report a 90% confidence upper limit on the rate of binary IMBH mergers with nonspinning and equal mass components of 6.9×10^(−8) Mpc^(−3) yr^(−1). We also report a rate upper limit for ringdown waveforms from perturbed IMBHs, radiating 1% of their mass as gravitational waves in the fundamental, ℓ=m=2, oscillation mode, that is nearly three orders of magnitude more stringent than previous results.
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“Residual amplitude modulation in interferometric gravitational wave detectors”, Journal of the Optical Society of America A (2014).
Keiko Kokeyama, Kiwamu Izumi, William Z. Korth, Nicolas Smith-Lefebvre, Koji Arai, and Rana X. AdhikariAbstract
The effects of residual amplitude modulation (RAM) in laser interferometers using heterodyne sensing can be substantial and difficult to mitigate. In this work, we analyze the effects of RAM on a complex laser interferometer used for gravitational wave detection. The RAM introduces unwanted offsets in the cavity length signals and thereby shifts the operating point of the optical cavities from the nominal point via feedback control. This shift causes variations in the sensing matrix, and leads to degradation in the performance of the precision noise subtraction scheme of the multiple-degree-of-freedom control system. In addition, such detuned optical cavities produce an optomechanical spring, which also perturbs the sensing matrix. We use our simulations to derive requirements on RAM for the Advanced LIGO (aLIGO) detectors, and show that the RAM expected in aLIGO will not limit its sensitivity.
Full text · DOI: 10.1364/josaa.31.000081
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“Quantum limits of interferometer topologies for gravitational radiation detection”, Classical and Quantum Gravity (2014).
Haixing Miao, Huan Yang, Rana X. Adhikari, and Yanbei ChenAbstract
In order to expand the astrophysical reach of gravitational wave (GW) detectors, several interferometer topologies have been proposed, in the past, to evade the thermodynamic and quantum mechanical limits in future detectors. In this work, we make a systematic comparison among these topologies by considering their sensitivities and complexities. We numerically optimize their sensitivities by introducing a cost function that tries to maximize the broadband improvement over the sensitivity of current detectors. We find that frequency-dependent squeezed-light injection with a 100 m scale filter cavity yields a good broadband sensitivity, with low complexity, and good robustness against optical loss. This study gives us a guideline for the near-term experimental research programs in enhancing the performance of future GW detectors.
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“Multimessenger search for sources of gravitational waves and high-energy neutrinos: Initial results for LIGO-Virgo and IceCube”, Physical Review D (2014).
M. G. Aartsen, J. Aasi, B. P. Abbott, R. Abbott, and M. R. Abernathy, et al.Abstract
We report the results of a multimessenger search for coincident signals from the LIGO and Virgo gravitational-wave observatories and the partially completed IceCube high-energy neutrino detector, including periods of joint operation between 2007–2010. These include parts of the 2005–2007 run and the 2009–2010 run for LIGO-Virgo, and IceCube's observation periods with 22, 59 and 79 strings. We find no significant coincident events, and use the search results to derive upper limits on the rate of joint sources for a range of source emission parameters. For the optimistic assumption of gravitational-wave emission energy of 10^(−2) M_⊙c^2 at ∼150 Hz with ∼60 ms duration, and high-energy neutrino emission of 10^(51) erg comparable to the isotropic gamma-ray energy of gamma-ray bursts, we limit the source rate below 1.6×10^(−2) Mpc^(−3) yr^(−1). We also examine how combining information from gravitational waves and neutrinos will aid discovery in the advanced gravitational-wave detector era.
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“Metrology and Coatings for the 40 kg LIGO Optics”, (2014).
Rana X. AdhikariAbstract
The 4 km LIGO interferometers seek to measure the gravitational radiation from cosmic explosions. In order to do so, their massive mirrors must meet several demanding specifications which are sometimes conflicting. I will described why the job is so challenging and how the challenges may be met.
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“Methods and results of a search for gravitational waves associated with gamma-ray bursts using the GEO 600, LIGO, and Virgo detectors”, Physical Review D (2014).
J. Aasi, B. P. Abbott, R. Abbott, M. R. Abernathy, and Rana X. Adhikari, et al.Abstract
In this paper we report on a search for short-duration gravitational wave bursts in the frequency range 64 Hz–1792 Hz associated with gamma-ray bursts (GRBs), using data from GEO 600 and one of the LIGO or Virgo detectors. We introduce the method of a linear search grid to analyze GRB events with large sky localization uncertainties, for example the localizations provided by the Fermi Gamma-ray Burst Monitor (GBM). Coherent searches for gravitational waves (GWs) can be computationally intensive when the GRB sky position is not well localized, due to the corrections required for the difference in arrival time between detectors. Using a linear search grid we are able to reduce the computational cost of the analysis by a factor of O(10) for GBM events. Furthermore, we demonstrate that our analysis pipeline can improve upon the sky localization of GRBs detected by the GBM, if a high-frequency GW signal is observed in coincidence. We use the method of the linear grid in a search for GWs associated with 129 GRBs observed satellite-based gamma-ray experiments between 2006 and 2011. The GRBs in our sample had not been previously analyzed for GW counterparts. A fraction of our GRB events are analyzed using data from GEO 600 while the detector was using squeezed-light states to improve its sensitivity; this is the first search for GWs using data from a squeezed-light interferometric observatory. We find no evidence for GW signals, either with any individual GRB in this sample or with the population as a whole. For each GRB we place lower bounds on the distance to the progenitor, under an assumption of a fixed GW emission energy of 10^(−2)M⊙c^2, with a median exclusion distance of 0.8 Mpc for emission at 500 Hz and 0.3 Mpc at 1 kHz. The reduced computational cost associated with a linear search grid will enable rapid searches for GWs associated with Fermi GBM events once the advanced LIGO and Virgo detectors begin operation.
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“Instrumental vetoes for transient gravitational-wave triggers using noise-coupling models: The bilinear-coupling veto”, Physical Review D (2014).
Parameswaran Ajith, Tomoki Isogai, Nelson Christensen, Rana X. Adhikari, Aaron B. Pearlman, Alex Wein, Alan J. Weinstein, and Ben YuanAbstract
The Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo recently completed searches for gravitational waves at their initial target sensitivities, and soon Advanced LIGO and Advanced Virgo will commence observations with even better capabilities. In the search for short-duration signals, such as coalescing compact binary inspirals or "burst" events, noise transients can be problematic. Interferometric gravitational-wave detectors are highly complex instruments, and, based on the experience from the past, the data often contain a large number of noise transients that are not easily distinguishable from possible gravitational-wave signals. In order to perform a sensitive search for short-duration gravitational-wave signals it is important to identify these noise artifacts, and to "veto" them. Here we describe such a veto, the bilinear-coupling veto, that makes use of an empirical model of the coupling of instrumental noise to the output strain channel of the interferometric gravitational-wave detector. In this method, we check whether the data from the output strain channel at the time of an apparent signal is consistent with the data from a bilinear combination of auxiliary channels. We discuss the results of the application of this veto to recent LIGO data, and its possible utility when used with data from Advanced LIGO and Advanced Virgo.
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“Improved Upper Limits on the Stochastic Gravitational-Wave Background from 2009–2010 LIGO and Virgo Data”, Physical Review Letters (2014).
J. Aasi, B. P. Abbott, R. Abbott, M. R. Abernathy, and R. X. Adhikari, et al.Abstract
Gravitational waves from a variety of sources are predicted to superpose to create a stochastic background. This background is expected to contain unique information from throughout the history of the Universe that is unavailable through standard electromagnetic observations, making its study of fundamental importance to understanding the evolution of the Universe. We carry out a search for the stochastic background with the latest data from the LIGO and Virgo detectors. Consistent with predictions from most stochastic gravitational-wave background models, the data display no evidence of a stochastic gravitational-wave signal. Assuming a gravitational-wave spectrum of Ω_(GW)(f)=Ω_α(f/f_(ref))_α, we place 95% confidence level upper limits on the energy density of the background in each of four frequency bands spanning 41.5–1726 Hz. In the frequency band of 41.5–169.25 Hz for a spectral index of α=0, we constrain the energy density of the stochastic background to be Ω_(GW)(f)<5.6×10^(−6). For the 600–1000 Hz band, Ω_(GW)(f)<0.14(f/900 Hz)^3, a factor of 2.5 lower than the best previously reported upper limits. We find Ω_(GW)(f)<1.8×10^(−4) using a spectral index of zero for 170–600 Hz and Ω_(GW)(f)<1.0(f/1300 Hz)^3 for 1000–1726 Hz, bands in which no previous direct limits have been placed. The limits in these four bands are the lowest direct measurements to date on the stochastic background. We discuss the implications of these results in light of the recent claim by the BICEP2 experiment of the possible evidence for inflationary gravitational waves.
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“Implementation of an F-statistic all-sky search for continuous gravitational waves in Virgo VSR1 data”, Classical and Quantum Gravity (2014).
J. Aasi, B. P. Abbott, R. Abbott, M. R. Abernathy, and R. X. Adhikari, et al.Abstract
We present an implementation of the F-statistic to carry out the first search in data from the Virgo laser interferometric gravitational wave detector for periodic gravitational waves from a priori unknown, isolated rotating neutron stars. We searched a frequency f_0 range from 100 Hz to 1 kHz and the frequency dependent spindown f_1 range from -1.6(f_0/100 Hz) x 10^(-9) Hz s^(−1) to zero. A large part of this frequency–spindown space was unexplored by any of the all-sky searches published so far. Our method consisted of a coherent search over two-day periods using the F-statistic, followed by a search for coincidences among the candidates from the two-day segments. We have introduced a number of novel techniques and algorithms that allow the use of the fast Fourier transform (FFT) algorithm in the coherent part of the search resulting in a fifty-fold speed-up in computation of the F-statistic with respect to the algorithm used in the other pipelines. No significant gravitational wave signal was found. The sensitivity of the search was estimated by injecting signals into the data. In the most sensitive parts of the detector band more than 90% of signals would have been detected with dimensionless gravitational-wave amplitude greater than 5 x 10^(-24).
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“Gravitational-waves from known pulsars: results from the initial detector era”, Astrophysical Journal (2014).
J. Aasi, J. Abadie, B. P. Abbott, R. Abbott, and M. R. Abernathy, et al.Abstract
We present the results of searches for gravitational waves from a large selection of pulsars using data from the most recent science runs (S6, VSR2 and VSR4) of the initial generation of interferometric gravitational wave detectors LIGO (Laser Interferometric Gravitational-wave Observatory) and Virgo. We do not see evidence for gravitational wave emission from any of the targeted sources but produce upper limits on the emission amplitude. We highlight the results from seven young pulsars with large spin-down luminosities. We reach within a factor of five of the canonical spin-down limit for all seven of these, whilst for the Crab and Vela pulsars we further surpass their spin-down limits. We present new or updated limits for 172 other pulsars (including both young and millisecond pulsars). Now that the detectors are undergoing major upgrades, and, for completeness, we bring together all of the most up-to-date results from all pulsars searched for during the operations of the first-generation LIGO, Virgo and GEO600 detectors. This gives a total of 195 pulsars including the most recent results described in this paper.
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“Gravitational radiation detection with laser interferometry”, Reviews of Modern Physics (2014).
Rana X. AdhikariAbstract
Gravitational-wave detection has been pursued relentlessly for over 40 years. With the imminent operation of a new generation of laser interferometers, it is expected that detections will become a common occurrence. The research into more ambitious detectors promises to allow the field to move beyond detection and into the realm of precision science using gravitational radiation. In this article, the state of art for the detectors is reviewed and an outlook for the coming decades is described.
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“First Searches for Optical Counterparts to Gravitational-Wave Candidate Events”, Astrophysical Journal Supplement Series (2014).
J. Aasi, J. Abadie, B. P. Abbott, R. Abbott, and M. R. Abernathy, et al.Abstract
During the Laser Interferometer Gravitational-wave Observatory and Virgo joint science runs in 2009-2010, gravitational wave (GW) data from three interferometer detectors were analyzed within minutes to select GW candidate events and infer their apparent sky positions. Target coordinates were transmitted to several telescopes for follow-up observations aimed at the detection of an associated optical transient. Images were obtained for eight such GW candidates. We present the methods used to analyze the image data as well as the transient search results. No optical transient was identified with a convincing association with any of these candidates, and none of the GW triggers showed strong evidence for being astrophysical in nature. We compare the sensitivities of these observations to several model light curves from possible sources of interest, and discuss prospects for future joint GW-optical observations of this type.
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“First all-sky search for continuous gravitational waves from unknown sources in binary systems”, Physical Review D (2014).
J. Aasi, B. P. Abbott, R. Abbott, M. R. Abernathy, and R. X. Adhikari, et al.Abstract
We present the first results of an all-sky search for continuous gravitational waves from unknown spinning neutron stars in binary systems using LIGO and Virgo data. Using a specially developed analysis program, the TwoSpect algorithm, the search was carried out on data from the sixth LIGO science run and the second and third Virgo science runs. The search covers a range of frequencies from 20 Hz to 520 Hz, a range of orbital periods from 2 to ∼2,254 h and a frequency- and period-dependent range of frequency modulation depths from 0.277 to 100 mHz. This corresponds to a range of projected semimajor axes of the orbit from ∼0.6×10^(−3) ls to ∼6,500 ls assuming the orbit of the binary is circular. While no plausible candidate gravitational wave events survive the pipeline, upper limits are set on the analyzed data. The most sensitive 95% confidence upper limit obtained on gravitational wave strain is 2.3×10^(−24) at 217 Hz, assuming the source waves are circularly polarized. Although this search has been optimized for circular binary orbits, the upper limits obtained remain valid for orbital eccentricities as large as 0.9. In addition, upper limits are placed on continuous gravitational wave emission from the low-mass x-ray binary Scorpius X-1 between 20 Hz and 57.25 Hz.
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“Dark matter: Time for detection”, Nature Physics (2014).
Rana X. Adhikari, Paul Hamilton, and Holger MüllerAbstract
Multiple lines of astrophysical evidence suggest that over one-quarter of the mass of the Universe takes the form of dark matter, with a density in our Solar System of roughly one hydrogen atom's mass per cubic metre. Most attempts to directly detect dark matter have focused on particles such as weakly interacting massive particles (WIMPs) or axions. Enormous detectors searching for dark matter have been built. They are looking for signals such as tiny flashes of light from collisions between dark matter and liquid xenon, phonons created by collisions in germanium, or microwaves generated by axions in a resonant cavity. Yet so far, dark matter has passed through the Earth undetected. An alternative explanation is that dark matter acts more like a classical, spatially dependent field. Writing in Nature Physics, Andrei Derevianko and Maxim Pospelov now suggest searching for such a field using a world-wide network of atomic clocks to register any changes in the their ticking rate as the Earth passes through dark matter.
Full text · DOI: 10.1038/nphys3175
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“Constraints on Cosmic Strings from the LIGO-Virgo Gravitational-Wave Detectors”, Physical Review Letters (2014).
J. Aasi, J. Abadie, B. P. Abbott, R. Abbott, and M. R. Abernathy, et al.Abstract
Measurements are presented by the CMS Collaboration at the Large Hadron Collider (LHC) of the higher-order harmonic coefficients that describe the azimuthal anisotropy of charged particles emitted in sNN−−−√=2.76 TeV PbPb collisions. Expressed in terms of the Fourier components of the azimuthal distribution, the n=3–6 harmonic coefficients are presented for charged particles as a function of their transverse momentum (0.3
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“Concepts and research for future detectors - Summary of the Amaldi 10 C4 session”, General Relativity and Gravitation (2014).
F. Acernese and R. X. AdhikariAbstract
Technologies, design aspects and recent progresses for future gravitational wave (GW) detectors are mentioned in this summary of the C4 session of the Amaldi 10 conference.
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“Application of a Hough search for continuous gravitational waves on data from the fifth LIGO science run”, Classical and Quantum Gravity (2014).
J. Aasi, J. Abadie, B. P. Abbott, R. Abbott, and M. R. Abernathy, et al.Abstract
We report on an all-sky search for periodic gravitational waves in the frequency range 50–1000 Hz with the first derivative of frequency in the range −8.9 × 10^(−10) Hz s^(−1) to zero in two years of data collected during LIGO's fifth science run. Our results employ a Hough transform technique, introducing a χ^2 test and analysis of coincidences between the signal levels in years 1 and 2 of observations that offers a significant improvement in the product of strain sensitivity with compute cycles per data sample compared to previously published searches. Since our search yields no surviving candidates, we present results taking the form of frequency dependent, 95% confidence upper limits on the strain amplitude h0. The most stringent upper limit from year 1 is 1.0 × 10^(−24) in the 158.00–158.25 Hz band. In year 2, the most stringent upper limit is 8.9 × 10^(−25) in the 146.50–146.75 Hz band. This improved detection pipeline, which is computationally efficient by at least two orders of magnitude better than our flagship Einstein@Home search, will be important for 'quick-look' searches in the Advanced LIGO and Virgo detector era.
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“Achieving resonance in the Advanced LIGO gravitational-wave interferometer”, Classical and Quantum Gravity (2014).
A. Staley, D. Martynov, R. Abbott, R. X. Adhikari, K. Arai, A. F. Brooks, J. G. Rollins, N. D. Smith-Lefebvre, and G. VajenteAbstract
Interferometric gravitational-wave detectors are complex instruments comprised of a Michelson interferometer enhanced by multiple coupled cavities. Active feedback control is required to operate these instruments and keep the cavities locked on resonance. The optical response is highly nonlinear until a good operating point is reached. The linear operating range is between 0.01% and 1% of a fringe for each degree of freedom. The resonance lock has to be achieved in all five degrees of freedom simultaneously, making the acquisition difficult. Furthermore, the cavity linewidth seen by the laser is only _(~1) Hz, which is four orders of magnitude smaller than the linewidth of the free running laser. The arm length stabilization system is a new technique used for arm cavity locking in Advanced LIGO. Together with a modulation technique utilizing third harmonics to lock the central Michelson interferometer, the Advanced LIGO detector has been successfully locked and brought to an operating point where detecting gravitational-waves becomes feasible.
2013
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“Suppression of quantum-radiation-pressure noise in an optical spring”, Physical Review A (2013).
W. Zach Korth, Haixing Miao, Thomas Corbitt, Garrett D. Cole, Yanbei Chen, and Rana X. AdhikariAbstract
Recent advances in micro- and nanofabrication techniques have led to corresponding improvement in the performance of optomechanical systems, which provide a promising avenue towards quantum-limited metrology and the study of quantum behavior in macroscopic mechanical objects. One major impediment to reaching the quantum regime is thermal excitation, which can be overcome for a sufficiently high mechanical quality factor Q. Here, we propose a method for increasing the effective Q of a mechanical resonator by stiffening it via the optical spring effect exhibited by linear optomechanical systems and show how the associated quantum-radiation-pressure noise can be evaded by sensing and feedback control. In a parameter regime that is attainable with current technology, this method allows for realistic quantum cavity optomechanics in a frequency band well below that which has been realized thus far.
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“Search for long-lived gravitational-wave transients coincident with long gamma-ray bursts”, Physical Review D (2013).
J. Aasi, J. Abadie, B. P. Abbott, R. Abbott, and M. R. Abernathy, et al.Abstract
Long gamma-ray bursts (GRBs) have been linked to extreme core-collapse supernovae from massivestars. Gravitational waves (GW) offer a probe of the physics behind long GRBs. We investigate models of long-lived (~10–1000 s) GW emission associated with the accretion disk of a collapsed star or with its protoneutron star remnant. Using data from LIGO's fifth science run, and GRB triggers from the Swift experiment, we perform a search for unmodeled long-lived GW transients. Finding no evidence of GW emission, we place 90% confidence-level upper limits on the GW fluence at Earth from long GRBs for three waveforms inspired by a model of GWs from accretion disk instabilities. These limits range from F < 3:5 ergs cm^(-2) to F < 1200 ergs cm^(-2), depending on the GRB and on the model, allowing us to probe optimistic scenarios of GW production out to distances as far as ≈ 33 Mpc. Advanced detectors are expected to achieve strain sensitivities 10x better than initial LIGO, potentially allowing us to probe the engines of the nearest long GRBs.
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“Search for gravitational waves from binary black hole inspiral, merger, and ringdown in LIGO-Virgo data from 2009–2010”, Physical Review D (2013).
J. Aasi, J. Abadie, B. P. Abbott, R. Abbott, and Rana X. Adhikari, et al.Abstract
We report a search for gravitational waves from the inspiral, merger and ringdown of binary black holes (BBH) with total mass between 25 and 100 solar masses, in data taken at the LIGO and Virgo observatories between July 7, 2009 and October 20, 2010. The maximum sensitive distance of the detectors over this period for a (20,20)M_⊙ coalescence was 300 Mpc. No gravitational wave signals were found. We thus report upper limits on the astrophysical coalescence rates of BBH as a function of the component masses for nonspinning components, and also evaluate the dependence of the search sensitivity on component spins aligned with the orbital angular momentum. We find an upper limit at 90% confidence on the coalescence rate of BBH with nonspinning components of mass between 19 and 28M_⊙ of 3.3×10^(-7) mergers Mpc^(-3) yr^(-1).
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“Parameter estimation for compact binary coalescence signals with the first generation gravitational-wave detector network”, Physical Review D (2013).
J. Aasi, J. Abadie, B. P. Abbott, R. Abbott, and Rana X. Adhikari, et al.Abstract
Compact binary systems with neutron stars or black holes are one of the most promising sources for ground-based gravitational-wave detectors. Gravitational radiation encodes rich information about source physics; thus parameter estimation and model selection are crucial analysis steps for any detection candidate events. Detailed models of the anticipated waveforms enable inference on several parameters, such as component masses, spins, sky location and distance, that are essential for new astrophysical studies of these sources. However, accurate measurements of these parameters and discrimination of models describing the underlying physics are complicated by artifacts in the data, uncertainties in the waveform models and in the calibration of the detectors. Here we report such measurements on a selection of simulated signals added either in hardware or software to the data collected by the two LIGO instruments and the Virgo detector during their most recent joint science run, including a "blind injection" where the signal was not initially revealed to the collaboration. We exemplify the ability to extract information about the source physics on signals that cover the neutron-star and black-hole binary parameter space over the component mass range 1 M_⊙–25 M_⊙ and the full range of spin parameters. The cases reported in this study provide a snapshot of the status of parameter estimation in preparation for the operation of advanced detectors.
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“Enhanced sensitivity of the LIGO gravitational wave detector by using squeezed states of light”, Nature Photonics (2013).
J. Aasi, J. Abadie, B. P. Abbott, R. Abbott, and M. R. Abernathy, et al.Abstract
Nearly a century after Einstein first predicted the existence of gravitational waves, a global network of Earth-based gravitational wave observatories is seeking to directly detect this faint radiation using precision laser interferometry. Photon shot noise, due to the quantum nature of light, imposes a fundamental limit on the attometre-level sensitivity of the kilometre-scale Michelson interferometers deployed for this task. Here, we inject squeezed states to improve the performance of one of the detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) beyond the quantum noise limit, most notably in the frequency region down to 150 Hz, critically important for several astrophysical sources, with no deterioration of performance observed at any frequency. With the injection of squeezed states, this LIGO detector demonstrated the best broadband sensitivity to gravitational waves ever achieved, with important implications for observing the gravitational-wave Universe with unprecedented sensitivity.
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“Einstein@Home all-sky search for periodic gravitational waves in LIGO S5 data”, Physical Review D (2013).
J. Aasi, J. Abadie, B. P. Abbott, R. Abbott, and Rana X. Adhikari, et al.Abstract
This paper presents results of an all-sky search for periodic gravitational waves in the frequency range [50,1 190] Hz and with frequency derivative range of ∼[-20,1.1]×10^(-10) Hz s^(-1) for the fifth LIGO science run (S5). The search uses a noncoherent Hough-transform method to combine the information from coherent searches on time scales of about one day. Because these searches are very computationally intensive, they have been carried out with the Einstein@Home volunteer distributed computing project. Postprocessing identifies eight candidate signals; deeper follow-up studies rule them out. Hence, since no gravitational wave signals have been found, we report upper limits on the intrinsic gravitational wave strain amplitude h_0. For example, in the 0.5 Hz-wide band at 152.5 Hz, we can exclude the presence of signals with h_0 greater than 7.6×10^(-25) at a 90% confidence level. This search is about a factor 3 more sensitive than the previous Einstein@Home search of early S5 LIGO data.
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“Directed search for continuous gravitational waves from the Galactic center”, Physical Review D (2013).
J. Aasi, J. Abadie, R. Abbott, M. R. Abernathy, and R. X. Adhikari, et al.Abstract
We present the results of a directed search for continuous gravitational waves from unknown, isolated neutron stars in the Galactic center region, performed on two years of data from LIGO's fifth science run from two LIGO detectors. The search uses a semicoherent approach, analyzing coherently 630 segments, each spanning 11.5 hours, and then incoherently combining the results of the single segments. It covers gravitational wave frequencies in a range from 78 to 496 Hz and a frequency-dependent range of first-order spindown values down to −7.86×10^(−8) Hz/s at the highest frequency. No gravitational waves were detected. The 90% confidence upper limits on the gravitational wave amplitude of sources at the Galactic center are ∼3.35×10^(−25) for frequencies near 150 Hz. These upper limits are the most constraining to date for a large-parameter-space search for continuous gravitational wave signals.
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“Brownian thermal noise in multilayer coated mirrors”, Physical Review D (2013).
Ting Hong, Huan Yang, Eric K. Gustafson, Rana X. Adhikari, and Yanbei ChenAbstract
We analyze the Brownian thermal noise of a multilayer dielectric coating used in high-precision optical measurements, including interferometric gravitational-wave detectors. We assume the coating material to be isotropic, and therefore study thermal noises arising from shear and bulk losses of the coating materials. We show that coating noise arises not only from layer thickness fluctuations, but also from fluctuations of the interface between the coating and substrate, driven by fluctuating shear stresses of the coating. Although thickness fluctuations of different layers are statistically independent, there exists a finite coherence between the layers and the substrate-coating interface. In addition, photoelastic coefficients of the thin layers (so far not accurately measured) further influence the thermal noise, although at a relatively low level. Taking into account uncertainties in material parameters, we show that significant uncertainties still exist in estimating coating Brownian noise.
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“Angular control of optical cavities in a radiation-pressure-dominated regime: the Enhanced LIGO case”, Journal of the Optical Society of America A (2013).
Katherine L. Dooley, Lisa Barsotti, Rana X. Adhikari, Matthew Evans, Tobin T. Fricke, Peter Fritschel, Valera Frolov, Keita Kawabe, and Nicolás Smith-LefebvreAbstract
We describe the angular sensing and control (ASC) of 4 km detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO). Enhanced LIGO, the culmination of the first generation LIGO detectors, operated between 2009 and 2010 with about 40 kW of laser power in the arm cavities. In this regime, radiation-pressure effects are significant and induce instabilities in the angular opto-mechanical transfer functions. Here we present and motivate the ASC design in this extreme case and present the results of its implementation in Enhanced LIGO. Highlights of the ASC performance are successful control of opto-mechanical torsional modes, relative mirror motions of ≤ 1×10^−7 rad rms, and limited impact on in-band strain sensitivity.
Full text · DOI: 10.1364/josaa.30.002618
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“A first search for coincident gravitational waves and high energy neutrinos using LIGO, Virgo and ANTARES data from 2007”, Journal of Cosmology and Astroparticle Physics (2013).
S. Adrián-Martínez, J. Aasi, J. Abadie, B. P. Abbott, and R. Abbott, et al.Abstract
We present the results of the first search for gravitational wave bursts associated with high energy neutrinos. Together, these messengers could reveal new, hidden sources that are not observed by conventional photon astronomy, particularly at high energy. Our search uses neutrinos detected by the underwater neutrino telescope ANTARES in its 5 line configuration during the period January - September 2007, which coincided with the fifth and first science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed for candidate gravitational-wave signals coincident in time and direction with the neutrino events. No significant coincident events were observed. We place limits on the density of joint high energy neutrino - gravitational wave emission events in the local universe, and compare them with densities of merger and core-collapse events.
2012
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“Upper limits on a stochastic gravitational-wave background using LIGO and Virgo interferometers at 600–1000 Hz”, Physical Review D (2012).
J. Abadie, B. P. Abbott, R. Abbott, Rana X. Adhikari, and P. Ajith, et al.Abstract
A stochastic background of gravitational waves is expected to arise from a superposition of many incoherent sources of gravitational waves, of either cosmological or astrophysical origin. This background is a target for the current generation of ground-based detectors. In this article we present the first joint search for a stochastic background using data from the LIGO and Virgo interferometers. In a frequency band of 600–1000 Hz, we obtained a 95% upper limit on the amplitude of Ω_(GW)(f)=Ω_3(f/900 Hz)^3, of Ω_3<0.32, assuming a value of the Hubble parameter of h_(100)=0.71. These new limits are a factor of seven better than the previous best in this frequency band.
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“The characterization of Virgo data and its impact on gravitational-wave searches”, Classical and Quantum Gravity (2012).
J. Aasi, J. Abadie, B. P. Abbott, R. Abbott, and Rana X. Adhikari, et al.Abstract
Between 2007 and 2010 Virgo collected data in coincidence with the LIGO and GEO gravitational-wave (GW) detectors. These data have been searched for GWs emitted by cataclysmic phenomena in the universe, by non-axisymmetric rotating neutron stars or from a stochastic background in the frequency band of the detectors. The sensitivity of GW searches is limited by noise produced by the detector or its environment. It is therefore crucial to characterize the various noise sources in a GW detector. This paper reviews the Virgo detector noise sources, noise propagation, and conversion mechanisms which were identified in the three first Virgo observing runs. In many cases, these investigations allowed us to mitigate noise sources in the detector, or to selectively flag noise events and discard them from the data. We present examples from the joint LIGO-GEO-Virgo GW searches to show how well noise transients and narrow spectral lines have been identified and excluded from the Virgo data. We also discuss how detector characterization can improve the astrophysical reach of GW searches.
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“Technique for in situ measurement of free spectral range and transverse mode spacing of optical cavities”, Applied Optics (2012).
Alberto Stochino, Koji Arai, and Rana X. AdhikariAbstract
Length and g-factor are fundamental parameters that characterize optical cavities. We developed a technique to measure these parameters in situ by determining the frequency spacing between the resonances of fundamental and spatial modes of an optical cavity. Two laser beams are injected into the cavity, and their relative frequency is scanned by a phase-lock loop, while the cavity is locked to either laser. The measurement of the amplitude of their beat note in transmission reveals the resonances of the longitudinal and the transverse modes of the cavity and their spacing. This method proves particularly useful to characterize complex optical systems, including very long and/or coupled optical cavities, as in gravitational-wave interferometers. This technique and the results of its application to the coupled cavities of a 40 m-long gravitational-wave interferometer prototype are presented here.
Full text · DOI: 10.1364/ao.51.006571
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“Swift Follow-up Observations of Candidate Gravitational-wave Transient Events”, Astrophysical Journal Supplement Series (2012).
P. A. Evans, J. Aasi, J. Abadie, B. P. Abbott, and R. Abbott, et al.Abstract
We present the first multi-wavelength follow-up observations of two candidate gravitational-wave (GW) transient events recorded by LIGO and Virgo in their 2009-2010 science run. The events were selected with low latency by the network of GW detectors (within less than 10 minutes) and their candidate sky locations were observed by the Swift observatory (within 12 hr). Image transient detection was used to analyze the collected electromagnetic data, which were found to be consistent with background. Off-line analysis of the GW data alone has also established that the selected GW events show no evidence of an astrophysical origin; one of them is consistent with background and the other one was a test, part of a "blind injection challenge." With this work we demonstrate the feasibility of rapid follow-ups of GW transients and establish the sensitivity improvement joint electromagnetic and GW observations could bring. This is a first step toward an electromagnetic follow-up program in the regime of routine detections with the advanced GW instruments expected within this decade. In that regime, multi-wavelength observations will play a significant role in completing the astrophysical identification of GW sources. We present the methods and results from this first combined analysis and discuss its implications in terms of sensitivity for the present and future instruments.
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“Subtraction of Newtonian noise using optimized sensor arrays”, Physical Review D (2012).
Jennifer C. Driggers, Jan Harms, and Rana X. AdhikariAbstract
Fluctuations in the local Newtonian gravitational field present a limit to high precision measurements, including searches for gravitational waves using laser interferometers. In this work, we present a model of this perturbing gravitational field and evaluate schemes to mitigate the effect by estimating and subtracting it from the interferometer data stream. Information about the Newtonian noise is obtained from simulated seismic data. The method is tested on causal as well as acausal implementations of noise subtraction. In both cases it is demonstrated that broadband mitigation factors close to 10 can be achieved removing Newtonian noise as a dominant noise contribution. The resulting improvement in the detector sensitivity will substantially enhance the detection rate of gravitational radiation from cosmological sources.
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“Search for gravitational waves from low mass compact binary coalescence in LIGO's sixth science run and Virgo's science runs 2 and 3”, Physical Review D (2012).
J. Abadie, B. P. Abbott, R. Abbott, Rana X. Adhikari, and P. Ajith, et al.Abstract
We report on a search for gravitational waves from coalescing compact binaries using LIGO and Virgo observations between July 7, 2009, and October 20, 2010. We searched for signals from binaries with total mass between 2 and 25M_⊙; this includes binary neutron stars, binary black holes, and binaries consisting of a black hole and neutron star. The detectors were sensitive to systems up to 40 Mpc distant for binary neutron stars, and further for higher mass systems. No gravitational-wave signals were detected. We report upper limits on the rate of compact binary coalescence as a function of total mass, including the results from previous LIGO and Virgo observations. The cumulative 90% confidence rate upper limits of the binary coalescence of binary neutron star, neutron star-black hole, and binary black hole systems are 1.3×10^(-4), 3.1×10^(-5), and 6.4×10^(-6) Mpc^(-3) yr^(-1), respectively. These upper limits are up to a factor 1.4 lower than previously derived limits. We also report on results from a blind injection challenge.
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“Search for gravitational waves from intermediate mass binary black holes”, Physical Review D (2012).
J. Abadie, B. P. Abbott, R. Abbott, Rana X. Adhikari, and P. Ajith, et al.Abstract
We present the results of a weakly modeled burst search for gravitational waves from mergers of nonspinning intermediate mass black holes in the total mass range 100–450 M_⊙ and with the component mass ratios between 1:1 and 4:1. The search was conducted on data collected by the LIGO and Virgo detectors between November of 2005 and October of 2007. No plausible signals were observed by the search which constrains the astrophysical rates of the intermediate mass black holes mergers as a function of the component masses. In the most efficiently detected bin centered on 88+88 M_⊙, for nonspinning sources, the rate density upper limit is 0.13 per Mpc^3 per Myr at the 90% confidence level.
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“Search for Gravitational Waves Associated with Gamma-Ray Bursts during LIGO Science Run 6 and Virgo Science Runs 2 and 3”, Astrophysical Journal (2012).
J. Abadie, B. P. Abbott, R. Abbott, R. X. Adhikari, and P. Ajith, et al.Abstract
We present the results of a search for gravitational waves associated with 154 gamma-ray bursts (GRBs) that were detected by satellite-based gamma-ray experiments in 2009-2010, during the sixth LIGO science run and the second and third Virgo science runs. We perform two distinct searches: a modeled search for coalescences of either two neutron stars or a neutron star and black hole, and a search for generic, unmodeled gravitational-wave bursts. We find no evidence for gravitational-wave counterparts, either with any individual GRB in this sample or with the population as a whole. For all GRBs we place lower bounds on the distance to the progenitor, under the optimistic assumption of a gravitational-wave emission energy of 10^(–2) M_☉ c^2 at 150 Hz, with a median limit of 17 Mpc. For short-hard GRBs we place exclusion distances on binary neutron star and neutron-star-black-hole progenitors, using astrophysically motivated priors on the source parameters, with median values of 16 Mpc and 28 Mpc, respectively. These distance limits, while significantly larger than for a search that is not aided by GRB satellite observations, are not large enough to expect a coincidence with a GRB. However, projecting these exclusions to the sensitivities of Advanced LIGO and Virgo, which should begin operation in 2015, we find that the detection of gravitational waves associated with GRBs will become quite possible.
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“Multicolor cavity metrology”, Journal of the Optical Society of America A (2012).
Kiwamu Izumi, Koji Arai, Bryan Barr, Joseph Betzwieser, Aidan Brooks, Katrin Dahl, Suresh Doravari, Jennifer C. Driggers, W. Zach Korth, Haixing Miao, Jameson Rollins, Stephen Vass, David Yeaton-Massey, and Rana X. AdhikariAbstract
Long-baseline laser interferometers used for gravitational-wave detection have proven to be very complicated to control. In order to have sufficient sensitivity to astrophysical gravitational waves, a set of multiple coupled optical cavities comprising the interferometer must be brought into resonance with the laser field. A set of multi-input, multi-output servos then lock these cavities into place via feedback control. This procedure, known as lock acquisition, has proven to be a vexing problem and has reduced greatly the reliability and duty factor of the past generation of laser interferometers. In this article, we describe a technique for bringing the interferometer from an uncontrolled state into resonance by using harmonically related external fields to provide a deterministic hierarchical control. This technique reduces the effect of the external seismic disturbances by 4 orders of magnitude and promises to greatly enhance the stability and reliability of the current generation of gravitational-wave detectors. The possibility for using multicolor techniques to overcome current quantum and thermal noise limits is also discussed.
Full text · DOI: 10.1364/josaa.29.002092
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“Large-angle scattered light measurements for quantum-noise filter cavity design studies”, Journal of the Optical Society of America A (2012).
Fabian Magaña-Sandoval, Rana X. Adhikari, Valera Frolov, Jan Harms, Jacqueline Lee, Shannon Sankar, Peter R. Saulson, and Joshua R. SmithAbstract
Optical loss from scattered light could limit the performance of quantum-noise filter cavities being considered for an upgrade to the Advanced Laser Interferometer Gravitational Wave Observatory (LIGO) gravitational-wave detectors. This paper describes imaging scatterometer measurements of the large-angle scattered light from two high-quality sample optics, a high reflector and a beamsplitter. These optics are each superpolished fused silica substrates with silica:tantala dielectric coatings. They represent the current state-of-the art optical technology for use in filter cavities. We present angle-resolved scatter values and integrate these to estimate the total scatter over the measured angles. We find that the total integrated light scattered into larger angles can be as small as 4 ppm.
Full text · DOI: 10.1364/josaa.29.001722
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“Implications for the Origin of GRB 051103 from LIGO Observations”, Astrophysical Journal (2012).
J. Abadie, B. P. Abbott, R. Abbott, Rana X. Adhikari, and P. Ajith, et al.Abstract
We present the results of a LIGO search for gravitational waves (GWs) associated with GRB 051103, a short-duration hard-spectrum gamma-ray burst (GRB) whose electromagnetically determined sky position is coincident with the spiral galaxy M81, which is 3.6 Mpc from Earth. Possible progenitors for short-hard GRBs include compact object mergers and soft gamma repeater (SGR) giant flares. A merger progenitor would produce a characteristic GW signal that should be detectable at a distance of M81, while GW emission from an SGR is not expected to be detectable at that distance. We found no evidence of a GW signal associated with GRB 051103. Assuming weakly beamed γ-ray emission with a jet semi-angle of 30°, we exclude a binary neutron star merger in M81 as the progenitor with a confidence of 98%. Neutron star-black hole mergers are excluded with >99% confidence. If the event occurred in M81, then our findings support the hypothesis that GRB 051103 was due to an SGR giant flare, making it one of the most distant extragalactic magnetars observed to date.
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“Implementation and testing of the first prompt search for gravitational wave transients with electromagnetic counterparts”, Astronomy and Astrophysics (2012).
J. Abadie, B. P. Abbott, R. Abbott, Rana X. Adhikari, and P. Ajith, et al.Abstract
Aims. A transient astrophysical event observed in both gravitational wave (GW) and electromagnetic (EM) channels would yield rich scientific rewards. A first program initiating EM follow-ups to possible transient GW events has been developed and exercised by the LIGO and Virgo community in association with several partners. In this paper, we describe and evaluate the methods used to promptly identify and localize GW event candidates and to request images of targeted sky locations. Methods. During two observing periods (Dec. 17, 2009 to Jan. 8, 2010 and Sep. 2 to Oct. 20, 2010), a low-latency analysis pipeline was used to identify GW event candidates and to reconstruct maps of possible sky locations. A catalog of nearby galaxies and Milky Way globular clusters was used to select the most promising sky positions to be imaged, and this directional information was delivered to EM observatories with time lags of about thirty minutes. A Monte Carlo simulation has been used to evaluate the low-latency GW pipeline's ability to reconstruct source positions correctly. Results. For signals near the detection threshold, our low-latency algorithms often localized simulated GW burst signals to tens of square degrees, while neutron star/neutron star inspirals and neutron star/black hole inspirals were localized to a few hundred square degrees. Localization precision improves for moderately stronger signals. The correct sky location of signals well above threshold and originating from nearby galaxies may be observed with ~50% or better probability with a few pointings of wide-field telescopes.
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“Global feed-forward vibration isolation in a km scale interferometer”, Classical and Quantum Gravity (2012).
Ryan DeRosa, Jennifer C. Driggers, Dani Atkinson, Haixing Miao, Valery Frolov, Michael Landry, Joseph A. Giaime, and Rana X. AdhikariAbstract
Using a network of seismometers and sets of optimal filters, we implemented a feed-forward control technique to minimize the seismic contribution to multiple interferometric degrees of freedom of the Laser Interferometer Gravitational-wave Observatory interferometers. The filters are constructed by using the Levinson–Durbin recursion relation to approximate the optimal Wiener filter. By reducing the RMS of the interferometer feedback signals below ~10 Hz, we have improved the stability and duty cycle of the joint network of gravitational wave detectors. By suppressing the large control forces and mirror motions, we have dramatically reduced the rate of non-Gaussian transients in the gravitational wave signal stream.
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“First low-latency LIGO+Virgo search for binary inspirals and their electromagnetic counterparts”, Astronomy and Astrophysics (2012).
J. Abadie, B. P. Abbott, R. Abbott, Rana X. Adhikari, and P. Ajith, et al.Abstract
Aims. The detection and measurement of gravitational-waves from coalescing neutron-star binary systems is an important science goal for ground-based gravitational-wave detectors. In addition to emitting gravitational-waves at frequencies that span the most sensitive bands of the LIGO and Virgo detectors, these sources are also amongst the most likely to produce an electromagnetic counterpart to the gravitational-wave emission. A joint detection of the gravitational-wave and electromagnetic signals would provide a powerful new probe for astronomy. Methods. During the period between September 19 and October 20, 2010, the first low-latency search for gravitational-waves from binary inspirals in LIGO and Virgo data was conducted. The resulting triggers were sent to electromagnetic observatories for followup. We describe the generation and processing of the low-latency gravitational-wave triggers. The results of the electromagnetic image analysis will be described elsewhere. Results. Over the course of the science run, three gravitational-wave triggers passed all of the low-latency selection cuts. Of these, one was followed up by several of our observational partners. Analysis of the gravitational-wave data leads to an estimated false alarm rate of once every 6.4 days, falling far short of the requirement for a detection based solely on gravitational-wave data.
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“DC readout experiment in Enhanced LIGO”, Classical and Quantum Gravity (2012).
Tobin T. Fricke, Nicolás D. Smith-Lefebvre, Richard Abbott, Rana X. Adhikari, Katherine L. Dooley, Matthew Evans, Peter Fritschel, Valery V. Frolov, Keita Kawabe, Jeffrey S. Kissel, Bram J. J. Slagmolen, and Sam J. WaldmanAbstract
The two 4 km long gravitational wave detectors operated by the Laser Interferometer Gravitational-wave Observatory (LIGO) were modified in 2008 to read out the gravitational wave channel using the DC readout form of homodyne detection and to include an optical filter cavity at the output of the detector. As part of the upgrade to Enhanced LIGO, these modifications replaced the radio-frequency (RF) heterodyne system used previously. We describe the motivations for and the implementation of DC readout and the output mode cleaner in Enhanced LIGO. We present characterizations of the system, including measurements and models of the couplings of the noises from the laser source to the gravitational wave readout channel. We show that noise couplings using DC readout are improved over those for RF readout, and we find that the achieved shot-noise-limited sensitivity is consistent with modeled results.
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“All-sky search for periodic gravitational waves in the full S5 LIGO data”, Physical Review D (2012).
J. Abadie, B. P. Abbott, Rana X. Adhikari, P. Ajith, and S. B. Anderson, et al.Abstract
We report on an all-sky search for periodic gravitational waves in the frequency band 50–800 Hz and with the frequency time derivative in the range of 0 through -6×10^(-9) Hz/s. Such a signal could be produced by a nearby spinning and slightly nonaxisymmetric isolated neutron star in our Galaxy. After recent improvements in the search program that yielded a 10× increase in computational efficiency, we have searched in two years of data collected during LIGO's fifth science run and have obtained the most sensitive all-sky upper limits on gravitational-wave strain to date. Near 150 Hz our upper limit on worst-case linearly polarized strain amplitude h_0 is 1×10^(-24), while at the high end of our frequency range we achieve a worst-case upper limit of 3.8×10^(-24) for all polarizations and sky locations. These results constitute a factor of 2 improvement upon previously published data. A new detection pipeline utilizing a loosely coherent algorithm was able to follow up weaker outliers, increasing the volume of space where signals can be detected by a factor of 10, but has not revealed any gravitational-wave signals. The pipeline has been tested for robustness with respect to deviations from the model of an isolated neutron star, such as caused by a low-mass or long-period binary companion.
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“All-sky search for gravitational-wave bursts in the second joint LIGO-Virgo run”, Physical Review D (2012).
J. Abadie, B. P. Abbott, R. Abbott, Rana X. Adhikari, and P. Ajith, et al.Abstract
We present results from a search for gravitational-wave bursts in the data collected by the LIGO and Virgo detectors between July 7, 2009 and October 20, 2010: data are analyzed when at least two of the three LIGO-Virgo detectors are in coincident operation, with a total observation time of 207 days. The analysis searches for transients of duration ≲1 s over the frequency band 64–5000 Hz, without other assumptions on the signal waveform, polarization, direction or occurrence time. All identified events are consistent with the expected accidental background. We set frequentist upper limits on the rate of gravitational-wave bursts by combining this search with the previous LIGO-Virgo search on the data collected between November 2005 and October 2007. The upper limit on the rate of strong gravitational-wave bursts at the Earth is 1.3 events per year at 90% confidence. We also present upper limits on source rate density per year and Mpc^3 for sample populations of standard-candle sources. As in the previous joint run, typical sensitivities of the search in terms of the root-sum-squared strain amplitude for these waveforms lie in the range ∼5×10^(-22) Hz^(-1/2) to ∼1×10^(-20) Hz^(-1/2). The combination of the two joint runs entails the most sensitive all-sky search for generic gravitational-wave bursts and synthesizes the results achieved by the initial generation of interferometric detectors.
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“Active noise cancellation in a suspended interferometer”, Review of Scientific Instruments (2012).
J. C. Driggers, Matthew Evans, and Rana X. AdhikariAbstract
We demonstrate feed-forward vibration isolation on a suspended Fabry-Perot interferometer using Wiener filtering and a variant of the common least mean square adaptive filter algorithm. We compare the experimental results with theoretical estimates of the cancellation efficiency. Using data from the recent Laser Interferometer Gravitational Wave Observatory (LIGO) Science Run, we also estimate the impact of this technique on full scale gravitational wave interferometers. In the future, we expect to use this technique also to remove acoustic, magnetic, and gravitational noise perturbations from the LIGO interferometers. This noise cancellation technique is simple enough to implement in standard laboratory environments and can be used to improve signal-to-noise ratio for a variety of high precision experiments.
Full text · DOI: 10.1063/1.3675891
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“A new bound on excess frequency noise in second harmonic generation in PPKTP at the 10^(−19) level”, Optics Express (2012).
D. Yeaton-Massey and R. X. AdhikariAbstract
We report a bound on the relative frequency fluctuations in nonlinear second harmonic generation. A 1064nm Nd:YAG laser is used to read out the phase of a Mach-Zehnder interferometer while PPKTP, a nonlinear crystal, is placed in each arm to generate second harmonic light. By comparing the arm length difference of the Mach Zehnder as read out by the fundamental 1064 nm light, and its second harmonic at 532 nm, we can bound the excess frequency noise introduced in the harmonic generation process. We report an amplitude spectral density of frequency noise with total RMS frequency deviation of 3mHz and a minimum value of 20 μHz/Hz^(1/2) over 250 seconds with a measurement bandwidth of 128 Hz, corresponding to an Allan deviation of 10^(−19) at 20 seconds.
Full text · DOI: 10.1364/oe.20.021019
2011
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“Search for gravitational waves from binary black hole inspiral, merger, and ringdown”, Physical Review D (2011).
B. P. Abbott, J. Abadie, R. Abbott, Rana X. Adhikari, and P. Ajith, et al.Abstract
We present the first modeled search for gravitational waves using the complete binary black-hole gravitational waveform from inspiral through the merger and ringdown for binaries with negligible component spin. We searched approximately 2 years of LIGO data, taken between November 2005 and September 2007, for systems with component masses of 1–99M_⊙ and total masses of 25–100M_⊙. We did not detect any plausible gravitational-wave signals but we do place upper limits on the merger rate of binary black holes as a function of the component masses in this range. We constrain the rate of mergers for 19M_⊙ ≤ m_1, m_2 ≤ 28M_⊙ binary black-hole systems with negligible spin to be no more than 2.0 Mpc^(-3) Myr^(-1) at 90% confidence.
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“Search for gravitational waves associated with the August 2006 timing glitch of the Vela pulsar”, Physical Review D (2011).
J. Abadie, R. Abbott, B. P. Abbott, Rana X. Adhikari, and P. Ajith, et al.Abstract
The physical mechanisms responsible for pulsar timing glitches are thought to excite quasinormal mode oscillations in their parent neutron star that couple to gravitational-wave emission. In August 2006, a timing glitch was observed in the radio emission of PSR B0833-45, the Vela pulsar. At the time of the glitch, the two colocated Hanford gravitational-wave detectors of the Laser Interferometer Gravitational wave observatory (LIGO) were operational and taking data as part of the fifth LIGO science run (S5). We present the first direct search for the gravitational-wave emission associated with oscillations of the fundamental quadrupole mode excited by a pulsar timing glitch. No gravitational-wave detection candidate was found. We place Bayesian 90% confidence upper limits of 6.3 x 10^(-21) to 1.4 x 10^(-20) on the peak intrinsic strain amplitude of gravitational-wave ring-down signals, depending on which spherical harmonic mode is excited. The corresponding range of energy upper limits is 5.0 x 10^(-44) to 1.3 x 10^(-45) erg.
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“Search for Gravitational Wave Bursts from Six Magnetars”, Astrophysical Journal Letters (2011).
J. Abadie, B. P. Abbott, R. Abbott, Rana X. Adhikari, and S. B. Anderson, et al.Abstract
Soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are thought to be magnetars: neutron stars powered by extreme magnetic fields. These rare objects are characterized by repeated and sometimes spectacular gamma-ray bursts. The burst mechanism might involve crustal fractures and excitation of non-radial modes which would emit gravitational waves (GWs). We present the results of a search for GW bursts from six galactic magnetars that is sensitive to neutron star f-modes, thought to be the most efficient GW emitting oscillatory modes in compact stars. One of them, SGR 0501+4516, is likely ~1 kpc from Earth, an order of magnitude closer than magnetars targeted in previous GW searches. A second, AXP 1E 1547.0–5408, gave a burst with an estimated isotropic energy >10^(44) erg which is comparable to the giant flares. We find no evidence of GWs associated with a sample of 1279 electromagnetic triggers from six magnetars occurring between 2006 November and 2009 June, in GW data from the LIGO, Virgo, and GEO600 detectors. Our lowest model-dependent GW emission energy upper limits for band- and time-limited white noise bursts in the detector sensitive band, and for f-mode ringdowns (at 1090 Hz), are 3.0 × 10^(44) d^2_1 erg and 1.4 × 10^(47) d^2_1 erg, respectively, where d_1 = ^(d0501)_(1kpc) and d_ (0501) is the distance to SGR 0501+4516. These limits on GW emission from f-modes are an order of magnitude lower than any previous, and approach the range of electromagnetic energies seen in SGR giant flares for the first time.
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“Effects of mirror aberrations on Laguerre-Gaussian beams in interferometric gravitational-wave detectors”, Physical Review D (2011).
T. Hong, J. Miller, H. Yamamoto, Y. Chen, and Rana X. AdhikariAbstract
A fundamental limit to the sensitivity of optical interferometers is imposed by Brownian thermal fluctuations of the mirrors' surfaces. This thermal noise can be reduced by using larger beams which "average out" the random fluctuations of the surfaces. It has been proposed previously that wider, higher-order Laguerre-Gaussian modes can be used to exploit this effect. In this paper, we show that susceptibility to spatial imperfections of the mirrors' surfaces limits the effectiveness of this approach in interferometers used for gravitational-wave detection. Possible methods of reducing this susceptibility are also discussed.
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“Directional Limits on Persistent Gravitational Waves Using LIGO S5 Science Data”, Physical Review Letters (2011).
J. Abadie, R. W. P. Drever, J. Harms, M. Boyle, and Y. Chen, et al.Abstract
The gravitational-wave (GW) sky may include nearby pointlike sources as well as stochastic backgrounds. We perform two directional searches for persistent GWs using data from the LIGO S5 science run: one optimized for pointlike sources and one for arbitrary extended sources. Finding no evidence to support the detection of GWs, we present 90% confidence level (C.L.) upper-limit maps of GW strain power with typical values between 2-20×10^(-50) strain^2 Hz^(-1) and 5-35×10^(-49) strain^2 Hz^(-1) sr^(-1) for pointlike and extended sources, respectively. The latter result is the first of its kind. We also set 90% C.L. limits on the narrow-band root-mean-square GW strain from interesting targets including Sco X-1, SN 1987A and the Galactic center as low as ≈7×10^(-25) in the most sensitive frequency range near 160 Hz.
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“Beating the Spin-down Limit on Gravitational Wave Emission from the Vela Pulsar”, Astrophysical Journal (2011).
J. Abadie, B. P. Abbott, R. Abbott, Rana X. Adhikari, and S. B. Anderson, et al.Abstract
We present direct upper limits on continuous gravitational wave emission from the Vela pulsar using data from the Virgo detector's second science run. These upper limits have been obtained using three independent methods that assume the gravitational wave emission follows the radio timing. Two of the methods produce frequentist upper limits for an assumed known orientation of the star's spin axis and value of the wave polarization angle of, respectively, 1.9 × 10^(–24) and 2.2 × 10^(–24), with 95% confidence. The third method, under the same hypothesis, produces a Bayesian upper limit of 2.1 × 10^(–24), with 95% degree of belief. These limits are below the indirect spin-down limit of 3.3 × 10^(–24) for the Vela pulsar, defined by the energy loss rate inferred from observed decrease in Vela's spin frequency, and correspond to a limit on the star ellipticity of ~10^(–3). Slightly less stringent results, but still well below the spin-down limit, are obtained assuming the star's spin axis inclination and the wave polarization angles are unknown.
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“A gravitational wave observatory operating beyond the quantum shot-noise limit”, Nature Physics (2011).
J. Abadie, A. Marandi, B. P. Abbott, R. Abbott, and R. Adhikari, et al.Abstract
Around the globe several observatories are seeking the first direct detection of gravitational waves (GWs). These waves are predicted by Einstein's general theory of relativity and are generated, for example, by black-hole binary systems. Present GW detectors are Michelson-type kilometre-scale laser interferometers measuring the distance changes between mirrors suspended in vacuum. The sensitivity of these detectors at frequencies above several hundred hertz is limited by the vacuum (zero-point) fluctuations of the electromagnetic field. A quantum technology—the injection of squeezed light—offers a solution to this problem. Here we demonstrate the squeezed-light enhancement of GEO 600, which will be the GW observatory operated by the LIGO Scientific Collaboration in its search for GWs for the next 3–4 years. GEO 600 now operates with its best ever sensitivity, which proves the usefulness of quantum entanglement and the qualification of squeezed light as a key technology for future GW astronomy.
Full text · DOI: 10.1038/nphys2083
2010
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“Sensitivity to Gravitational Waves from Compact Binary Coalescences Achieved during LIGO's Fifth and Virgo's First Science Run”, (2010).
J. Abadie, B. P. Abbott, R. Abbott, M. Abernathy, and T. Accadia, et al.Abstract
We summarize the sensitivity achieved by the LIGO and Virgo gravitational wave detectors for compact binary coalescence (CBC) searches during LIGO's fifth science run and Virgo's first science run. We present noise spectral density curves for each of the four detectors that operated during these science runs which are representative of the typical performance achieved by the detectors for CBC searches. These spectra are intended for release to the public as a summary of detector performance for CBC searches during these science runs.
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“Searches for gravitational waves from known pulsars with S5 LIGO data”, Astrophysical Journal (2010).
B. P. Abbott, R. Abbott, R. Adhikari, S. B. Anderson, and M. Araya, et al.Abstract
We present a search for gravitational waves from 116 known millisecond and young pulsars using data from the fifth science run of the LIGO detectors. For this search, ephemerides overlapping the run period were obtained for all pulsars using radio and X-ray observations. We demonstrate an updated search method that allows for small uncertainties in the pulsar phase parameters to be included in the search. We report no signal detection from any of the targets and therefore interpret our results as upper limits on the gravitational wave signal strength. The most interesting limits are those for young pulsars. We present updated limits on gravitational radiation from the Crab pulsar, where the measured limit is now a factor of 7 below the spin-down limit. This limits the power radiated via gravitational waves to be less than ~2% of the available spin-down power. For the X-ray pulsar J0537 – 6910 we reach the spin-down limit under the assumption that any gravitational wave signal from it stays phase locked to the X-ray pulses over timing glitches, and for pulsars J1913+1011 and J1952+3252 we are only a factor of a few above the spin-down limit. Of the recycled millisecond pulsars, several of the measured upper limits are only about an order of magnitude above their spin-down limits. For these our best (lowest) upper limit on gravitational wave amplitude is 2.3 × 10^(–26) for J1603 – 7202 and our best (lowest) limit on the inferred pulsar ellipticity is 7.0 × 10^(–8) for J2124 – 3358.
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“Search for Gravitational-wave Inspiral Signals Associated with Short Gamma-ray Bursts During LIGO's Fifth and Virgo's First Science Run”, Astrophysical Journal (2010).
J. Abadie, B. P. Abbott, R. Abbott, Rana X. Adhikari, and P. Ajith, et al.Abstract
Progenitor scenarios for short gamma-ray bursts (short GRBs) include coalescenses of two neutron stars or a neutron star and black hole, which would necessarily be accompanied by the emission of strong gravitational waves. We present a search for these known gravitational-wave signatures in temporal and directional coincidence with 22 GRBs that had sufficient gravitational-wave data available in multiple instruments during LIGO's fifth science run, S5, and Virgo's first science run, VSR1. We find no statistically significant gravitational-wave candidates within a [ – 5, + 1) s window around the trigger time of any GRB. Using the Wilcoxon-Mann-Whitney U-test, we find no evidence for an excess of weak gravitational-wave signals in our sample of GRBs. We exclude neutron star-black hole progenitors to a median 90% confidence exclusion distance of 6.7 Mpc.
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“Search For Gravitational-wave Bursts Associated with Gamma-ray Bursts using Data from LIGO Science Run 5 and Virgo Science Run 1”, Astrophysical Journal (2010).
B. P. Abbott, R. Abbott, Rana X. Adhikari, S. B. Anderson, and M. Araya, et al.Abstract
We present the results of a search for gravitational-wave bursts (GWBs) associated with 137 gamma-ray bursts (GRBs) that were detected by satellite-based gamma-ray experiments during the fifth LIGO science run and first Virgo science run. The data used in this analysis were collected from 2005 November 4 to 2007 October 1, and most of the GRB triggers were from the Swift satellite. The search uses a coherent network analysis method that takes into account the different locations and orientations of the interferometers at the three LIGO-Virgo sites. We find no evidence for GWB signals associated with this sample of GRBs. Using simulated short-duration (<1 s) waveforms, we set upper limits on the amplitude of gravitational waves associated with each GRB. We also place lower bounds on the distance to each GRB under the assumption of a fixed energy emission in gravitational waves, with a median limit of D ~ 12 Mpc(E^(iso)_(GW)/0.01 M_☉ c ^(2)^(1/2) for emission at frequencies around 150 Hz, where the LIGO-Virgo detector network has best sensitivity. We present astrophysical interpretations and implications of these results, and prospects for corresponding searches during future LIGO-Virgo runs.
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“Search for gravitational waves from compact binary coalescence in LIGO and Virgo data from S5 and VSR1”, Physical Review D (2010).
J. Abadie, R. W. P. Drever, Michael Boyle, Y. Chen, and J. Luan, et al.Abstract
We report the results of the first search for gravitational waves from compact binary coalescence using data from the Laser Interferometer Gravitational-Wave Observatory and Virgo detectors. Five months of data were collected during the Laser Interferometer Gravitational-Wave Observatory's S5 and Virgo's VSR1 science runs. The search focused on signals from binary mergers with a total mass between 2 and 35M_⊙. No gravitational waves are identified. The cumulative 90%-confidence upper limits on the rate of compact binary coalescence are calculated for nonspinning binary neutron stars, black hole-neutron star systems, and binary black holes to be 8.7×10^(-3) yr^(-1) L_(10)^(-1), 2.2×10^(-3) yr^(-1) L_(10)^(-1), and 4.4×10^(-4) yr^(-1) L_(10)^(-1), respectively, where L_(10) is 10^(10) times the blue solar luminosity. These upper limits are compared with astrophysical expectations.
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“Predictions for the rates of compact binary coalescences observable by ground-based gravitational-wave detectors”, Classical and Quantum Gravity (2010).
J. Abadie, B. P. Abbott, R. Abbott, Rana X. Adhikari, and P. Ajith, et al.Abstract
We present an up-to-date, comprehensive summary of the rates for all types of compact binary coalescence sources detectable by the initial and advanced versions of the ground-based gravitational-wave detectors LIGO and Virgo. Astrophysical estimates for compact-binary coalescence rates depend on a number of assumptions and unknown model parameters and are still uncertain. Themost confident among these estimates are the rate predictions for coalescing binary neutron stars which are based on extrapolations from observed binary pulsars in our galaxy. These yield a likely coalescence rate of 100 Myr^(−1) per Milky Way Equivalent Galaxy (MWEG), although the rate could plausibly range from 1 Myr^(−1) MWEG^(−1) to 1000 Myr^(−1) MWEG^(−1) (Kalogera et al 2004 Astrophys. J. 601 L179; Kalogera et al 2004 Astrophys. J. 614 L137 (erratum)). We convert coalescence rates into detection rates based on data from the LIGO S5 and Virgo VSR2 science runs and projected sensitivities for our advanced detectors. Using the detector sensitivities derived from these data, we find a likely detection rate of 0.02 per year for Initial LIGO–Virgo interferometers, with a plausible range between 2 × 10^(−4) and 0.2 per year. The likely binary neutron–star detection rate for the Advanced LIGO–Virgo network increases to 40 events per year, with a range between 0.4 and 400 per year.
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“First search for gravitational waves from the youngest known neutron star”, Astrophysical Journal (2010).
J. Abadie, B. P. Abbott, R. Abbott, Rana X. Adhikari, and P. Ajith, et al.Abstract
We present a search for periodic gravitational waves from the neutron star in the supernova remnant Cassiopeia A. The search coherently analyzes data in a 12 day interval taken from the fifth science run of the Laser Interferometer Gravitational-Wave Observatory. It searches gravitational-wave frequencies from 100 to 300 Hz and covers a wide range of first and second frequency derivatives appropriate for the age of the remnant and for different spin-down mechanisms. No gravitational-wave signal was detected. Within the range of search frequencies, we set 95% confidence upper limits of (0.7–1.2) × 10^(−24) on the intrinsic gravitational-wave strain, (0.4–4) × 10^(−4) on the equatorial ellipticity of the neutron star, and 0.005–0.14 on the amplitude of r-mode oscillations of the neutron star. These direct upper limits beat indirect limits derived from energy conservation and enter the range of theoretical predictions involving crystalline exotic matter or runaway r-modes. This paper is also the first gravitational-wave search to present upper limits on the r-mode amplitude.
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“Calibration of the LIGO gravitational wave detectors in the fifth science run”, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment (2010).
J. Abadie, B. P. Abbott, R. Abbott, Rana X. Adhikari, and P. Ajith, et al.Abstract
The Laser Interferometer Gravitational Wave Observatory (LIGO) is a network of three detectors built to detect local perturbations in the space-time metric from astrophysical sources These detectors two in Hanford WA and one in Livingston LA are power-recycled Fabry-Perot Michelson interferometers In their fifth science run (S5) between November 2005 and October 2007 these detectors accumulated one year of triple coincident data while operating at their designed sensitivity In this paper we describe the calibration of the instruments in the S5 data set including measurement techniques and uncertainty estimation.
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“Angular instability due to radiation pressure in the LIGO gravitational-wave detector”, Applied Optics (2010).
Eiichi Hirose, Keita Kawabe, Daniel Sigg, Rana X. Adhikari, and Peter R. SaulsonAbstract
We observed the effect of radiation pressure on the angular sensing and control system of the Laser Interferometer Gravitational-Wave Observatory (LIGO) interferometer's core optics at LIGO Hanford Observatory. This is the first measurement of this effect in a complete gravitational-wave interferometer. Only one of the two angular modes survives with feedback control, because the other mode is suppressed when the control gain is sufficiently large. We developed a mathematical model to understand the physics of the system. This model matches well with the dynamics that we observe.
Full text · DOI: 10.1364/ao.49.003474
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“All-sky search for gravitational-wave bursts in the first joint LIGO-GEO-Virgo run”, Physical Review D (2010).
J. Abadie, B. P. Abbott, R. Abbott, Rana X. Adhikari, and P. Ajith, et al.Abstract
We present results from an all-sky search for unmodeled gravitational-wave bursts in the data collected by the LIGO, GEO 600 and Virgo detectors between November 2006 and October 2007. The search is performed by three different analysis algorithms over the frequency band 50–6000 Hz. Data are analyzed for times with at least two of the four LIGO-Virgo detectors in coincident operation, with a total live time of 266 days. No events produced by the search algorithms survive the selection cuts. We set a frequentist upper limit on the rate of gravitational-wave bursts impinging on our network of detectors. When combined with the previous LIGO search of the data collected between November 2005 and November 2006, the upper limit on the rate of detectable gravitational-wave bursts in the 64–2048 Hz band is 2.0 events per year at 90% confidence. We also present event rate versus strength exclusion plots for several types of plausible burst waveforms. The sensitivity of the combined search is expressed in terms of the root-sum-squared strain amplitude for a variety of simulated waveforms and lies in the range 6×10^(-22) Hz^(-1/2) to 2×10^(-20) Hz^(-1/2). This is the first untriggered burst search to use data from the LIGO and Virgo detectors together, and the most sensitive untriggered burst search performed so far.
2009
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“Stacked Search for Gravitational Waves from the 2006 SGR 1900+14 Storm”, Astrophysical Journal Letters (2009).
B. P. Abbott, R. Abbott, Rana X. Adhikari, P. Ajith, and B. Allen, et al.Abstract
We present the results of a LIGO search for short-duration gravitational waves (GWs) associated with the 2006 March 29 SGR 1900+14 storm. A new search method is used, "stacking" the GW data around the times of individual soft-gamma bursts in the storm to enhance sensitivity for models in which multiple bursts are accompanied by GW emission. We assume that variation in the time difference between burst electromagnetic emission and potential burst GW emission is small relative to the GW signal duration, and we time-align GW excess power time-frequency tilings containing individual burst triggers to their corresponding electromagnetic emissions. We use two GW emission models in our search: a fluence-weighted model and a flat (unweighted) model for the most electromagnetically energetic bursts. We find no evidence of GWs associated with either model. Model-dependent GW strain, isotropic GW emission energy E_(GW), and γ ≡ E_(GW)/E_(EM) upper limits are estimated using a variety of assumed waveforms. The stacking method allows us to set the most stringent model-dependent limits on transient GW strain published to date. We find E_(GW) upper limit estimates (at a nominal distance of 10 kpc) of between 2 × 10^(45) erg and 6 × 10^(50) erg depending on the waveform type. These limits are an order of magnitude lower than upper limits published previously for this storm and overlap with the range of electromagnetic energies emitted in soft gamma repeater (SGR) giant flares.
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“Search for high frequency gravitational-wave bursts in the first calendar year of LIGO's fifth science run”, Physical Review D (2009).
B. P. Abbott, R. Abbott, Rana X. Adhikari, P. Ajith, and B. Allen, et al.Abstract
We present an all-sky search for gravitational waves in the frequency range 1 to 6 kHz during the first calendar year of LIGO's fifth science run. This is the first untriggered LIGO burst analysis to be conducted above 3 kHz. We discuss the unique properties of interferometric data in this regime. 161.3 days of triple-coincident data were analyzed. No gravitational events above threshold were observed and a frequentist upper limit of 5.4 year^(-1) on the rate of strong gravitational-wave bursts was placed at a 90% confidence level. Implications for specific theoretical models of gravitational-wave emission are also discussed.
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“Search for gravitational-wave bursts in the first year of the fifth LIGO science run”, Physical Review D (2009).
B. P. Abbott, R. Abbott, Rana X. Adhikari, P. Ajith, and B. Allen, et al.Abstract
We present the results obtained from an all-sky search for gravitational-wave (GW) bursts in the 64– 2000 Hz frequency range in data collected by the LIGO detectors during the first year (November 2005— November 2006) of their fifth science run. The total analyzed live time was 268.6 days. Multiple hierarchical data analysis methods were invoked in this search. The overall sensitivity expressed in terms of the root-sum-square (rss) strain amplitude h_(rss) for gravitational-wave bursts with various morphologies was in the range of 6 x 10^(-22) Hz^(-1/2) to a few x 10^(-21) Hz^(-1/2). No GW signals were observed and a frequentist upper limit of 3.75 events per year on the rate of strong GW bursts was placed at the 90% confidence level. As in our previous searches, we also combined this rate limit with the detection efficiency for selected waveform morphologies to obtain event rate versus strength exclusion curves. In sensitivity, these exclusion curves are the most stringent to date.
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“Search for gravitational waves from low mass compact binary coalescence in 186 days of LIGO's fifth science run”, Physical Review D (2009).
B. P. Abbott, R. Abbott, Rana X. Adhikari, P. Ajith, and B. Allen, et al.Abstract
We report on a search for gravitational waves from coalescing compact binaries, of total mass between 2 and 35M_☉, using LIGO observations between November 14, 2006 and May 18, 2007. No gravitational-wave signals were detected. We report upper limits on the rate of compact binary coalescence as a function of total mass. The LIGO cumulative 90%-confidence rate upper limits of the binary coalescence of neutron stars, black holes and black hole-neutron star systems are 1.4 × 10^(-2), 7.3 × 10(-4) and 3.6 × 10(-3) yr(-1) L_10^(-1), respectively, where L_(10_ is 10^(10) times the blue solar luminosity
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“Search for gravitational waves from low mass binary coalescences in the first year of LIGO's S5 data”, Physical Review D (2009).
B. P. Abbott, R. Abbott, Rana X. Adhikari, P. Ajith, and B. Allen, et al.Abstract
We have searched for gravitational waves from coalescing low mass compact binary systems with a total mass between 2M_([sun]) and 35Mz-([sun]) and a minimum component mass of 1M_([sun]) using data from the first year of the fifth science run of the three LIGO detectors, operating at design sensitivity. Depending on the mass, we are sensitive to coalescences as far as 150 Mpc from the Earth. No gravitational-wave signals were observed above the expected background. Assuming a population of compact binary objects with a Gaussian mass distribution representing binary neutron star systems, black hole–neutron star binary systems, and binary black hole systems, we calculate the 90% confidence upper limit on the rate of coalescences to be 3.9×10^(-2) yr^(-1)L_(10)^(-1), 1.1×10^(-2) yr^(-1)L_(10)^(-1), and 2.5×10^(-3)yr^(-1)L_(10)^(-1), respectively, where L_(10) is 10^(10) times the blue solar luminosity. We also set improved upper limits on the rate of compact binary coalescences per unit blue-light luminosity, as a function of mass.
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“Search for gravitational wave ringdowns from perturbed black holes in LIGO S4 data”, Physical Review D (2009).
B. P. Abbott, R. Abbott, Rana X. Adhikari, P. Ajith, and B. Allen, et al.Abstract
According to general relativity a perturbed black hole will settle to a stationary configuration by the emission of gravitational radiation. Such a perturbation will occur, for example, in the coalescence of a black hole binary, following their inspiral and subsequent merger. At late times the waveform is a superposition of quasinormal modes, which we refer to as the ringdown. The dominant mode is expected to be the fundamental mode, l = m = 2. Since this is a well-known waveform, matched filtering can be implemented to search for this signal using LIGO data. We present a search for gravitational waves from black hole ringdowns in the fourth LIGO science run S4, during which LIGO was sensitive to the dominant mode of perturbed black holes with masses in the range of 10M_☉ to 500M_☉, the regime of intermediate-mass black holes, to distances up to 300 Mpc. We present a search for gravitational waves from black hole ringdowns using data from S4. No gravitational wave candidates were found; we place a 90%-confidence upper limit on the rate of ringdowns from black holes with mass between 85M_☉ and 390M_☉ in the local universe, assuming a uniform distribution of sources, of 3:2 X 10^(-5) yr^(-1) Mpc^(-3)= 1:6 X 10^(-3) yr^(-1)L_10-^1 L_(10) ; where L_(10) is 10^(10) times the solar blue-light luminosity.
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“Observation of a kilogram-scale oscillator near its quantum ground state”, New Journal of Physics (2009).
B. P. Abbott, R. Abbott, Rana X. Adhikari, P. Ajith, and B. Allen, et al.Abstract
We introduce a novel cooling technique capable of approaching the quantum ground state of a kilogram-scale system—an interferometric gravitational wave detector. The detectors of the Laser Interferometer Gravitational-wave Observatory (LIGO) operate within a factor of 10 of the standard quantum limit (SQL), providing a displacement sensitivity of 10^(−18) m in a 100 Hz band centered on 150 Hz. With a new feedback strategy, we dynamically shift the resonant frequency of a 2.7 kg pendulum mode to lie within this optimal band, where its effective temperature falls as low as 1.4 μK, and its occupation number reaches about 200 quanta. This work shows how the exquisite sensitivity necessary to detect gravitational waves can be made available to probe the validity of quantum mechanics on an enormous mass scale.
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“LIGO: the Laser Interferometer Gravitational-Wave Observatory”, Reports on Progress in Physics (2009).
B. P. Abbott, R. Abbott, Rana X. Adhikari, P Ajith, and B. Allen, et al.Abstract
The goal of the Laser Interferometric Gravitational-Wave Observatory (LIGO) is to detect and study gravitational waves (GWs) of astrophysical origin. Direct detection of GWs holds the promise of testing general relativity in the strong-field regime, of providing a new probe of exotic objects such as black holes and neutron stars and of uncovering unanticipated new astrophysics. LIGO, a joint Caltech–MIT project supported by the National Science Foundation, operates three multi-kilometer interferometers at two widely separated sites in the United States. These detectors are the result of decades of worldwide technology development, design, construction and commissioning. They are now operating at their design sensitivity, and are sensitive to gravitational wave strains smaller than one part in 10^(21). With this unprecedented sensitivity, the data are being analyzed to detect or place limits on GWs from a variety of potential astrophysical sources.
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“First LIGO search for gravitational wave bursts from cosmic (super)strings”, Physical Review D (2009).
B. P. Abbott, R. Abbott, Rana X. Adhikari, P. Ajith, and B. Allen, et al.Abstract
We report on a matched-filter search for gravitational wave bursts from cosmic string cusps using LIGO data from the fourth science run (S4) which took place in February and March 2005. No gravitational waves were detected in 14.9 days of data from times when all three LIGO detectors were operating. We interpret the result in terms of a frequentist upper limit on the rate of gravitational wave bursts and use the limits on the rate to constrain the parameter space (string tension, reconnection probability, and loop sizes) of cosmic string models. Many grand unified theory-scale models (with string tension Gµ/c^2[approximate]10^(-6)) can be ruled out at 90% confidence for reconnection probabilities p<=10^(-3) if loop sizes are set by gravitational back reaction.
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“Einstein@Home search for periodic gravitational waves in LIGO S4 data”, Physical Review D (2009).
B. P. Abbott, R. Abbott, Rana X. Adhikari, P Ajith, and B. Allen, et al.Abstract
A search for periodic gravitational waves, from sources such as isolated rapidly spinning neutron stars, was carried out using 510 h of data from the fourth LIGO science run (S4). The search was for quasimonochromatic waves in the frequency range from 50 to 1500 Hz, with a linear frequency drift _f (measured at the solar system barycenter) in the range -f/T < f <0: 1f/T, where the minimum spindown age T was 1000 yr for signals below 300 Hz and 10 000 yr above 300 Hz. The main computational work of the search was distributed over approximately 100 000 computers volunteered by the general public. This large computing power allowed the use of a relatively long coherent integration time of 30 h, despite the large parameter space searched. No statistically significant signals were found. The sensitivity of the search is estimated, along with the fraction of parameter space that was vetoed because of contamination by instrumental artifacts. In the 100 to 200 Hz band, more than 90% of sources with dimensionless gravitational-wave strain amplitude greater than 10^(-23) would have been detected.
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“Einstein@Home search for periodic gravitational waves in early S5 LIGO data”, Physical Review D (2009).
B. P. Abbott, R. Abbott, Rana X. Adhikari, P. Ajith, and B. Allen, et al.Abstract
This paper reports on an all-sky search for periodic gravitational waves from sources such as deformed isolated rapidly spinning neutron stars. The analysis uses 840 hours of data from 66 days of the fifth LIGO science run (S5). The data were searched for quasimonochromatic waves with frequencies f in the range from 50 to 1500 Hz, with a linear frequency drift _ƒ (measured at the solar system barycenter) in the range -ƒ/T < ƒ_ < 0:1ƒ/T, for a minimum spin-down age T of 1000 years for signals below 400 Hz and 8000 years above 400 Hz. The main computational work of the search was distributed over approximately 100 000 computers volunteered by the general public. This large computing power allowed the use of a relatively long coherent integration time of 30 hours while searching a large parameter space. This search extends Einstein@Home's previous search in LIGO S4 data to about 3 times better sensitivity. No statistically significant signals were found. In the 125–225 Hz band, more than 90% of sources with dimensionless gravitational-wave strain tensor amplitude greater than 3 X 10^(-24) would have been detected.
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“All-Sky LIGO Search for Periodic Gravitational Waves in the Early Fifth-Science-Run Data”, Physical Review Letters (2009).
B. P. Abbott, R. Abbott, Rana X. Adhikari, P. Ajith, and B. Allen, et al.Abstract
We report on an all-sky search with the LIGO detectors for periodic gravitational waves in the frequency range 50–1100 Hz and with the frequency's time derivative in the range -5 x 10^(-9)–0 Hzs^(-1). Data from the first eight months of the fifth LIGO science run (S5) have been used in this search, which is based on a semicoherent method (PowerFlux) of summing strain power. Observing no evidence of periodic gravitational radiation, we report 95% confidence-level upper limits on radiation emitted by any unknown isolated rotating neutron stars within the search range. Strain limits below 10^(-24) are obtained over a 200-Hz band, and the sensitivity improvement over previous searches increases the spatial volume sampled by an average factor of about 100 over the entire search band. For a neutron star with nominal equatorial ellipticity of 10^-6, the search is sensitive to distances as great as 500 pc.
2008
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“Search of S3 LIGO data for gravitational wave signals from spinning black hole and neutron star binary inspirals”, Physical Review D (2008).
B. Abbott, R. W. P. Drever, D. A. Brown, P. Savov, and X. Siemens, et al.Abstract
We report on the methods and results of the first dedicated search for gravitational waves emitted during the inspiral of compact binaries with spinning component bodies. We analyze 788 hours of data collected during the third science run (S3) of the LIGO detectors. We searched for binary systems using a detection template family specially designed to capture the effects of the spin-induced precession of the orbital plane. We present details of the techniques developed to enable this search for spin-modulated gravitational waves, highlighting the differences between this and other recent searches for binaries with nonspinning components. The template bank we employed was found to yield high matches with our spin-modulated target waveform for binaries with masses in the asymmetric range 1.0M⊙
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“Search for Gravitational-Wave Bursts from Soft Gamma Repeaters”, Physical Review Letters (2008).
B. Abbott, R. Abbott, Rana X. Adhikari, P. Ajith, and B. Allen, et al.Abstract
We present a LIGO search for short-duration gravitational waves (GWs) associated with soft gamma ray repeater (SGR) bursts. This is the first search sensitive to neutron star f modes, usually considered the most efficient GW emitting modes. We find no evidence of GWs associated with any SGR burst in a sample consisting of the 27 Dec. 2004 giant flare from SGR 1806-20 and 190 lesser events from SGR 1806-20 and SGR 1900+14. The unprecedented sensitivity of the detectors allows us to set the most stringent limits on transient GW amplitudes published to date. We find upper limit estimates on the model-dependent isotropic GW emission energies (at a nominal distance of 10 kpc) between 3×10^(45) and 9×10^(52) erg depending on waveform type, detector antenna factors and noise characteristics at the time of the burst. These upper limits are within the theoretically predicted range of some SGR models.
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“Search for gravitational waves from binary inspirals in S3 and S4 LIGO data”, Physical Review D (2008).
B. Abbott, R. W. P. Drever, D. A. Brown, P. Savov, and K. S. Thorne, et al.Abstract
We report on a search for gravitational waves from the coalescence of compact binaries during the third and fourth LIGO science runs. The search focused on gravitational waves generated during the inspiral phase of the binary evolution. In our analysis, we considered three categories of compact binary systems, ordered by mass: (i) primordial black hole binaries with masses in the range 0.35M_⊙
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“Search for gravitational waves associated with 39 gamma-ray bursts using data from the second, third, and fourth LIGO runs”, Physical Review D (2008).
B. Abbott, R. W. P. Drever, M. Tinto, D. A. Brown, and P. Savov, et al.Abstract
We present the results of a search for short-duration gravitational-wave bursts associated with 39 gamma-ray bursts (GRBs) detected by gamma-ray satellite experiments during LIGO's S2, S3, and S4 science runs. The search involves calculating the crosscorrelation between two interferometer data streams surrounding the GRB trigger time. We search for associated gravitational radiation from single GRBs, and also apply statistical tests to search for a gravitational-wave signature associated with the whole sample. For the sample examined, we find no evidence for the association of gravitational radiation with GRBs, either on a single-GRB basis or on a statistical basis. Simulating gravitational-wave bursts with sine-Gaussian waveforms, we set upper limits on the root-sum-square of the gravitational-wave strain amplitude of such waveforms at the times of the GRB triggers. We also demonstrate how a sample of several GRBs can be used collectively to set constraints on population models. The small number of GRBs and the significant change in sensitivity of the detectors over the three runs, however, limits the usefulness of a population study for the S2, S3, and S4 runs. Finally, we discuss prospects for the search sensitivity for the ongoing S5 run, and beyond for the next generation of detectors.
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“Implications for the origin of GRB 070201 from LIGO observations”, Astrophysical Journal (2008).
B. Abbott, R. Abbott, Rana X. Adhikari, J. Agresti, and P. Ajith, et al.Abstract
We analyzed the available LIGO data coincident with GRB 070201, a short-duration, hard-spectrum gamma-ray burst (GRB) whose electromagnetically determined sky position is coincident with the spiral arms of the Andromeda galaxy (M31). Possible progenitors of such short, hard GRBs include mergers of neutron stars or a neutron star and a black hole, or soft gamma-ray repeater (SGR) flares. These events can be accompanied by gravitational-wave emission. No plausible gravitational-wave candidates were found within a 180s long window around the time of GRB 070201. This result implies that a compact binary progenitor of GRB 070201, with masses in the range 1M☉ < m1 < 3M☉ and 1M☉ < m2 < 40M☉, located in M31 is excluded at > 99% confidence. If the GRB 070201 progenitor was not in M31, then we can exclude a binary neutron star merger progenitor with distance D < 3.5 Mpc, assuming random inclination, at 90% confidence. The result also implies that an unmodeled gravitational-wave burst from GRB 070201 most probably emitted less than 4.4×10^(-4) M☉c^2 (7.9×10^50 ergs) in any 100 ms long period within the signal region if the source was in M31 and radiated isotropically at the same frequency as LIGO's peak sensitivity (f ≈ 150 Hz). This upper limit does not exclude current models of SGRs at the M31 distance.
Full text · DOI: 10.1086/587954
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“First joint search for gravitational-wave bursts in LIGO and GEO 600 data”, Classical and Quantum Gravity (2008).
B. P. Abbott, R. Abbott, Rana X. Adhikari, P. Ajith, and B. Allen, et al.Abstract
We present the results of the first joint search for gravitational-wave bursts by the LIGO and GEO 600 detectors. We search for bursts with characteristic central frequencies in the band 768-2048 Hz in the data acquired between 22 February and 23 March, 2005 (fourth LSC Science Run-S4). We discuss the inclusion of the GEO 600 data in the Waveburst-CorrPower pipeline that first searches for coincident excess power events without taking into account differences in the antenna responses or strain sensitivities of the various detectors. We compare the performance of this pipeline to that of the coherent Waveburst pipeline based on the maximum likelihood statistic. This likelihood statistic is derived from a coherent sum of the detector data streams that takes into account the antenna patterns and sensitivities of the different detectors in the network. We find that the coherent Waveburst pipeline is sensitive to signals of amplitude 30-50% smaller than the Waveburst-CorrPower pipeline. We perform a search for gravitational-wave bursts using both pipelines and find no detection candidates in the S4 data set when all four instruments were operating stably.
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“dc readout experiment at the Caltech 40m prototype interferometer”, Classical and Quantum Gravity (2008).
R. L. Ward, Rana X. Adhikari, B. Abbott, R. Abbott, D. Barron, R. Bork, T. Fricke, V. Frolov, J. Heefner, A. Ivanov, O. Miyakawa, K. McKenzie, B. Slagmolen, M. Smith, R. Taylor, S. Vass, S. Waldman, and Alan J. WeinsteinAbstract
The Laser Interferometer Gravitational Wave Observatory (LIGO) operates a 40m prototype interferometer on the Caltech campus. The primary mission of the prototype is to serve as an experimental testbed for upgrades to the LIGO interferometers and for gaining experience with advanced interferometric techniques, including detuned resonant sideband extraction (i.e. signal recycling) and dc readout (optical homodyne detection). The former technique will be employed in Advanced LIGO, and the latter in both Enhanced and Advanced LIGO. Using dc readout for gravitational wave signal extraction has several technical advantages, including reduced laser and oscillator noise couplings as well as reduced shot noise, when compared to the traditional rf readout technique (optical heterodyne detection) currently in use in large-scale ground-based interferometric gravitational wave detectors. The Caltech 40m laboratory is currently prototyping a dc readout system for a fully suspended interferometric gravitational wave detector. The system includes an optical filter cavity at the interferometer's output port, and the associated controls and optics to ensure that the filter cavity is optimally coupled to the interferometer. We present the results of measurements to characterize noise couplings in rf and dc readout using this system.
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“Beating the spin-down limit on gravitational wave emission from the Crab pulsar”, Astrophysical Journal Letters (2008).
B. Abbott, R. Abbott, Rana X. Adhikari, P. Ajith, and B. Allen, et al.Abstract
We present direct upper limits on gravitational wave emission from the Crab pulsar using data from the first 9 months of the fifth science run of the Laser Interferometer Gravitational-wave Observatory (LIGO). These limits are based on two searches. In the first we assume that the gravitational wave emission follows the observed radio timing, giving an upper limit on gravitational wave emission that beats indirect limits inferred from the spin-down and braking index of the pulsar and the energetics of the nebula. In the second we allow for a small mismatch between the gravitational and radio signal frequencies and interpret our results in the context of two possible gravitational wave emission mechanisms.
Full text · DOI: 10.1086/591526
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“Astrophysically triggered searches for gravitational waves: status and prospects”, Classical and Quantum Gravity (2008).
B. Abbott, R. Abbott, Rana X. Adhikari, P. Ajith, and B. Allen, et al.Abstract
In gravitational-wave detection, special emphasis is put onto searches that focus on cosmic events detected by other types of astrophysical observatories. The astrophysical triggers, e. g. from gamma-ray and x-ray satellites, optical telescopes and neutrino observatories, provide a trigger time for analyzing gravitational-wave data coincident with the event. In certain cases the expected frequency range, source energetics, directional and progenitor information are also available. Beyond allowing the recognition of gravitational waveforms with amplitudes closer to the noise floor of the detector, these triggered searches should also lead to rich science results even before the onset of Advanced LIGO. In this paper we provide a broad review of LIGO's astrophysically triggered searches and the sources they target.
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“All-sky search for periodic gravitational waves in LIGO S4 data”, Physical Review D (2008).
B. Abbott, R. Abbott, Rana X. Adhikari, J. Agresti, and S. B. Anderson, et al.Abstract
We report on an all-sky search with the LIGO detectors for periodic gravitational waves in the frequency range 50–1000 Hz and with the frequency's time derivative in the range −1×10^(−8) Hz s^(−1) to zero. Data from the fourth LIGO science run (S4) have been used in this search. Three different semicoherent methods of transforming and summing strain power from short Fourier transforms (SFTs) of the calibrated data have been used. The first, known as StackSlide, averages normalized power from each SFT. A "weighted Hough" scheme is also developed and used, which also allows for a multi-interferometer search. The third method, known as PowerFlux, is a variant of the StackSlide method in which the power is weighted before summing. In both the weighted Hough and PowerFlux methods, the weights are chosen according to the noise and detector antenna-pattern to maximize the signal-to-noise ratio. The respective advantages and disadvantages of these methods are discussed. Observing no evidence of periodic gravitational radiation, we report upper limits; we interpret these as limits on this radiation from isolated rotating neutron stars. The best population-based upper limit with 95% confidence on the gravitational-wave strain amplitude, found for simulated sources distributed isotropically across the sky and with isotropically distributed spin axes, is 4.28×10^(−24) (near 140 Hz). Strict upper limits are also obtained for small patches on the sky for best-case and worst-case inclinations of the spin axes.
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“A quantum-enhanced prototype gravitational-wave detector”, Nature Physics (2008).
K. Goda, O. Miyakawa, E. E. Mikhailov, S. Saraf, R. Adhikari, K. McKenzie, R. Ward, S. Vass, A. J. Weinstein, and N. MavalvalaAbstract
The quantum nature of the electromagnetic field imposes a fundamental limit on the sensitivity of optical precision measurements such as spectroscopy, microscopy and interferometry. The so-called quantum limit is set by the zero-point fluctuations of the electromagnetic field, which constrain the precision with which optical signals can be measured. In the world of precision measurement, laser-interferometric gravitational-wave detectors, are the most sensitive position meters ever operated, capable of measuring distance changes of the order of 10- 18 m r.m.s. over kilometre separations caused by gravitational waves from astronomical sources. The sensitivity of currently operational and future gravitational-wave detectors is limited by quantum optical noise. Here, we demonstrate a 44% improvement in displacement sensitivity of a prototype gravitational-wave detector with suspended quasi-free mirrors at frequencies where the sensitivity is shot-noise-limited, by injecting a squeezed state of light. This demonstration is a critical step towards implementation of squeezing-enhancement in large-scale gravitational-wave detectors.
Full text · DOI: 10.1038/nphys920
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“A joint search for gravitational wave bursts with AURIGA and LIGO”, Classical and Quantum Gravity (2008).
L. Baggio, M. Bignotto, M. Bonaldi, M. Cerdonio, and M. De Rosa, et al.Abstract
The first simultaneous operation of the AURIGA detector and the LIGO observatory was an opportunity to explore real data, joint analysis methods between two very different types of gravitational wave detectors: resonant bars and interferometers. This paper describes a coincident gravitational wave burst search, where data from the LIGO interferometers are cross-correlated at the time of AURIGA candidate events to identify coincident transients. The analysis pipeline is tuned with two thresholds, on the signal-to-noise ratio of AURIGA candidate events and on the significance of the cross-correlation test in LIGO. The false alarm rate is estimated by introducing time shifts between data sets and the network detection efficiency is measured by adding simulated gravitational wave signals to the detector output. The simulated waveforms have a significant fraction of power in the narrower AURIGA band. In the absence of a detection, we discuss how to set an upper limit on the rate of gravitational waves and to interpret it according to different source models. Due to the short amount of analyzed data and to the high rate of non-Gaussian transients in the detectors' noise at the time, the relevance of this study is methodological: this was the first joint search for gravitational wave bursts among detectors with such different spectral sensitivity and the first opportunity for the resonant and interferometric communities to unify languages and techniques in the pursuit of their common goal.
2007
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“Upper limits on gravitational wave emission from 78 radio pulsars”, Physical Review D (2007).
B. Abbott, R. W. P. Drever, D. A. Brown, P. Savov, and X. Siemens, et al.Abstract
We present upper limits on the gravitational wave emission from 78 radio pulsars based on data from the third and fourth science runs of the LIGO and GEO 600 gravitational wave detectors. The data from both runs have been combined coherently to maximize sensitivity. For the first time, pulsars within binary (or multiple) systems have been included in the search by taking into account the signal modulation due to their orbits. Our upper limits are therefore the first measured for 56 of these pulsars. For the remaining 22, our results improve on previous upper limits by up to a factor of 10. For example, our tightest upper limit on the gravitational strain is 2.6×10^(−25) for PSR J1603−7202, and the equatorial ellipticity of PSR J2124–3358 is less than 10^(−6). Furthermore, our strain upper limit for the Crab pulsar is only 2.2 times greater than the fiducial spin-down limit.
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“Upper limit map of a background of gravitational waves”, Physical Review D (2007).
B. Abbott, R. W. P. Drever, P. Savov, X. Siemens, and K. S. Thorne, et al.Abstract
We searched for an anisotropic background of gravitational waves using data from the LIGO S4 science run and a method that is optimized for point sources. This is appropriate if, for example, the gravitational wave background is dominated by a small number of distinct astrophysical sources. No signal was seen. Upper limit maps were produced assuming two different power laws for the source strain power spectrum. For an f^(−3) power law and using the50 Hz to 1.8 kHz band the upper limits on the source strain power spectrum vary between 1.2×10^(−48) Hz^(−1) (100 Hz/f)^3 and 1.2×10^(−47) Hz^(−1) (100 Hz/f)^3, depending on the position in the sky. Similarly, in the case of constant strain power spectrum, the upper limits vary between 8.5×10−49 Hz−1 and 6.1×10^(−48) Hz^(−1). As a side product a limit on an isotropic background of gravitational waves was also obtained. All limits are at the 90% confidence level. Finally, as an application, we focused on the direction of Sco-X1, the brightest low-mass x-ray binary. We compare the upper limit on strain amplitude obtained by this method to expectations based on the x-ray flux from Sco-X1.
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“Searching for a Stochastic Background of Gravitational Waves with the Laser Interferometer Gravitational-Wave Observatory”, Astrophysical Journal (2007).
B. Abbott, R. Abbott, Rana X. Adhikari, J. Agresti, and S. B. Anderson, et al.Abstract
The Laser Interferometer Gravitational-Wave Observatory (LIGO) has performed the fourth science run, S4, with significantly improved interferometer sensitivities with respect to previous runs. Using data acquired during this science run, we place a limit on the amplitude of a stochastic background of gravitational waves. For a frequency independent spectrum, the new Bayesian 90% upper limit is Ω_(GW) × [H_0/(72 km s^(−1) Mpc^(−1))]^2 < 6.5 × 10^(-5). This is currently the most sensitive result in the frequency range 51-150 Hz, with a factor of 13 improvement over the previous LIGO result. We discuss the complementarity of the new result with other constraints on a stochastic background of gravitational waves, and we investigate implications of the new result for different models of this background.
Full text · DOI: 10.1086/511329
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“Searches for periodic gravitational waves from unknown isolated sources and Scorpius X-1: Results from the second LIGO science run”, Physical Review D (2007).
B. Abbott, R. W. P. Drever, M. Tinto, D. A. Brown, and C. Cutler, et al.Abstract
We carry out two searches for periodic gravitational waves using the most sensitive few hours of data from the second LIGO science run. Both searches exploit fully coherent matched filtering and cover wide areas of parameter space, an innovation over previous analyses which requires considerable algorithm development and computational power. The first search is targeted at isolated, previously unknown neutron stars, covers the entire sky in the frequency band 160–728.8 Hz, and assumes a frequency derivative of less than 4×10^(−10) Hz/s. The second search targets the accreting neutron star in the low-mass x-ray binary Scorpius X-1 and covers the frequency bands 464–484 Hz and 604–624 Hz as well as the two relevant binary orbit parameters. Because of the high computational cost of these searches we limit the analyses to the most sensitive 10 hours and 6 hours of data, respectively. Given the limited sensitivity and duration of the analyzed data set, we do not attempt deep follow-up studies. Rather we concentrate on demonstrating the data analysis method on a real data set and present our results as upper limits over large volumes of the parameter space. In order to achieve this, we look for coincidences in parameter space between the Livingston and Hanford 4-km interferometers. For isolated neutron stars our 95% confidence level upper limits on the gravitational wave strain amplitude range from 6.6×10^(−23) to 1×10^(−21) across the frequency band; for Scorpius X-1 they range from 1.7×10^(−22) to 1.3×10^(−21) across the two 20-Hz frequency bands. The upper limits presented in this paper are the first broadband wide parameter space upper limits on periodic gravitational waves from coherent search techniques. The methods developed here lay the foundations for upcoming hierarchical searches of more sensitive data which may detect astrophysical signals.
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“Search for gravitational-wave bursts in LIGO data from the fourth science run”, Classical and Quantum Gravity (2007).
B. Abbott, R. Abbott, Rana X. Adhikari, J. Agresti, and S. B. Anderson, et al.Abstract
The fourth science run of the LIGO and GEO 600 gravitational-wave detectors, carried out in early 2005, collected data with significantly lower noise than previous science runs. We report on a search for short-duration gravitational-wave bursts with arbitrary waveform in the 64–1600 Hz frequency range appearing in all three LIGO interferometers. Signal consistency tests, data quality cuts and auxiliary-channel vetoes are applied to reduce the rate of spurious triggers. No gravitational-wave signals are detected in 15.5 days of live observation time; we set a frequentist upper limit of 0.15 day^(−1) (at 90% confidence level) on the rate of bursts with large enough amplitudes to be detected reliably. The amplitude sensitivity of the search, characterized using Monte Carlo simulations, is several times better than that of previous searches. We also provide rough estimates of the distances at which representative supernova and binary black hole merger signals could be detected with 50% efficiency by this analysis.
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“Search for gravitational wave radiation associated with the pulsating tail of the SGR 1806-20 hyperflare of 27 December 2004 using LIGO”, Physical Review D (2007).
B. Abbott, R. W. P. Drever, D. A. Brown, P. Savov, and X. Siemens, et al.Abstract
We have searched for gravitational waves (GWs) associated with the SGR 1806−20 hyperflare of 27 December 2004. This event, originating from a Galactic neutron star, displayed exceptional energetics. Recent investigations of the x-ray light curve's pulsating tail revealed the presence of quasiperiodic oscillations (QPOs) in the 30–2000 Hz frequency range, most of which coincides with the bandwidth of the LIGO detectors. These QPOs, with well-characterized frequencies, can plausibly be attributed to seismic modes of the neutron star which could emit GWs. Our search targeted potential quasimonochromatic GWs lasting for tens of seconds and emitted at the QPO frequencies. We have observed no candidate signals above a predetermined threshold, and our lowest upper limit was set by the 92.5 Hz QPO observed in the interval from 150 s to 260 s after the start of the flare. This bound corresponds to a (90% confidence) root-sum-squared amplitude h^(90%)_(rss-det) =4.5×10^(−22) strain Hz^(−1/2) on the GW waveform strength in the detectable polarization state reaching our Hanford (WA) 4 km detector. We illustrate the astrophysical significance of the result via an estimated characteristic energy in GW emission that we would expect to be able to detect. The above result corresponds to 7.7×10^(46) erg (=4.3×10^(−8) M_⊙c^2), which is of the same order as the total (isotropic) energy emitted in the electromagnetic spectrum. This result provides a means to probe the energy reservoir of the source with the best upper limit on the GW waveform strength published and represents the first broadband asteroseismology measurement using a GW detector.
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“First cross-correlation analysis of interferometric and resonant-bar gravitational-wave data for stochastic backgrounds”, Physical Review D (2007).
B. Abbott, R. W. P. Drever, D. A. Brown, P. Savov, and X. Siemens, et al.Abstract
Data from the LIGO Livingston interferometer and the ALLEGRO resonant-bar detector, taken during LIGO's fourth science run, were examined for cross correlations indicative of a stochastic gravitational-wave background in the frequency range 850–950 Hz, with most of the sensitivity arising between 905 and 925 Hz. ALLEGRO was operated in three different orientations during the experiment to modulate the relative sign of gravitational-wave and environmental correlations. No statistically significant correlations were seen in any of the orientations, and the results were used to set a Bayesian 90% confidence level upper limit of Ω_(gw)(f)≤1.02, which corresponds to a gravitational-wave strain at 915 Hz of 1.5×10^(−23) Hz^(−1/2). In the traditional units of h^2_(100)Ω_(gw)(f), this is a limit of 0.53, 2 orders of magnitude better than the previous direct limit at these frequencies. The method was also validated with successful extraction of simulated signals injected in hardware and software.
2006
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“Search for gravitational-wave bursts in LIGO's third science run”, Classical and Quantum Gravity (2006).
B. Abbott, R. Abbott, Rana X. Adhikari, J. Agresti, and P. Ajith, et al.Abstract
We report on a search for gravitational-wave bursts in data from the three LIGO interferometric detectors during their third science run. The search targets subsecond bursts in the frequency range 100-1100 Hz for which no waveform model is assumed and has a sensitivity in terms of the root-sum-square (rss) strain amplitude of h(rss) ~10^(-20) Hz^(-1/2). No gravitational-wave signals were detected in the eight days of analysed data.
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“Search for gravitational waves from binary black hole inspirals in LIGO data”, Physical Review D (2006).
B. Abbott, R. Abbott, Rana X. Adhikari, A. Ageev, and J Agresti, et al.Abstract
We report on a search for gravitational waves from binary black hole inspirals in the data from the second science run of the LIGO interferometers. The search focused on binary systems with component masses between 3 and 20M_☉. Optimally oriented binaries with distances up to 1 Mpc could be detected with efficiency of at least 90%. We found no events that could be identified as gravitational waves in the 385.6 hours of data that we searched.
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“Measurement of optical response of a detuned resonant sideband extraction gravitational wave detector”, Physical Review D (2006).
Osamu Miyakawa, Robert Ward, Rana X. Adhikari, Matthew Evans, Benjamin Abbott, Rolf Bork, Daniel Busby, Jay Heefner, Alexander Ivanov, Michael Smith, Robert Taylor, Stephen Vass, Monica Varvella, Seiji Kawamura, Fumiko Kawazoe, Shihori Sakata, Conor Mow-Lowry, and Alan J. WeinsteinAbstract
We report on the optical response of a suspended-mass detuned resonant sideband extraction (RSE) interferometer with power recycling. The purpose of the detuned RSE configuration is to manipulate and optimize the optical response of the interferometer to differential displacements (induced by gravitational waves) as a function of frequency, independently of other parameters of the interferometer. The design of our interferometer results in an optical gain with two peaks: an RSE optical resonance at around 4 kHz and a radiation pressure induced optical spring at around 41 Hz. We have developed a reliable procedure for acquiring lock and establishing the desired optical configuration. In this configuration, we have measured the optical response to differential displacement and found good agreement with predictions at both resonances and all other relevant frequencies. These results build confidence in both the theory and practical implementation of the more complex optical configuration being planned for Advanced LIGO.
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“Lock Acquisition Scheme For The Advanced LIGO Optical configuration”, Journal of Physics: Conference Series (2006).
Osamu Miyakawa, Robert Ward, Rana X. Adhikari, Benjamin Abbott, Rolf Bork, Daniel Busby, Matthew Evans, Hartmut Grote, Jay Heefner, Alexander Ivanov, Seiji Kawamura, Fumiko Kawazoe, Shihori Sakata, Michael Smith, Robert Taylor, Monica Varvella, Stephen Vass, and Alan J. WeinsteinAbstract
The lock acquisition scheme for the Advanced LIGO optical configuration, which makes use of "resonant sideband extraction", is under investigation in the 40 meter prototype interferometer at Caltech. The 40m has a similar optical configuration to the one planned for Advanced LIGO which has 5 degrees of freedom for length control. So far we have succeeded in locking the 5 degrees of freedom routinely. The differential mode of arm cavities was locked in the same state as the final setup, and the peak of optical resonance was verified to be around 4 kHz. Currently, since an offset remains in the common mode of the arm cavities, another optical resonance can be seen in common mode optical gain.
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“Joint LIGO and TAMA300 search for gravitational waves from inspiralling neutron star binaries”, Physical Review D (2006).
B. Abbott, R. Abbott, R. Adhikari, A. Ageev, and J. Agresti, et al.Abstract
We search for coincident gravitational wave signals from inspiralling neutron star binaries using LIGO and TAMA300 data taken during early 2003. Using a simple trigger exchange method, we perform an intercollaboration coincidence search during times when TAMA300 and only one of the LIGO sites were operational. We find no evidence of any gravitational wave signals. We place an observational upper limit on the rate of binary neutron star coalescence with component masses between 1 and 3Mסּ of 49 per year per Milky Way equivalent galaxy at a 90% confidence level. The methods developed during this search will find application in future network inspiral analyses.
2005
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“Upper limits on gravitational wave bursts in LIGO's second science run”, Physical Review D (2005).
B. P. Abbott, R. Abbott, Rana X. Adhikari, A. Ageev, and J. Agresti, et al.Abstract
We perform a search for gravitational wave bursts using data from the second science run of the LIGO detectors, using a method based on a wavelet time-frequency decomposition. This search is sensitive to bursts of duration much less than a second and with frequency content in the 100–1100 Hz range. It features significant improvements in the instrument sensitivity and in the analysis pipeline with respect to the burst search previously reported by LIGO. Improvements in the search method allow exploring weaker signals, relative to the detector noise floor, while maintaining a low false alarm rate, O(0.1) μHz. The sensitivity in terms of the root-sum-square (rss) strain amplitude lies in the range of hrss∼10^-20 - 10^-19 Hz^-1/2. No gravitational wave signals were detected in 9.98 days of analyzed data. We interpret the search result in terms of a frequentist upper limit on the rate of detectable gravitational wave bursts at the level of 0.26 events per day at 90% confidence level. We combine this limit with measurements of the detection efficiency for selected waveform morphologies in order to yield rate versus strength exclusion curves as well as to establish order-of-magnitude distance sensitivity to certain modeled astrophysical sources. Both the rate upper limit and its applicability to signal strengths improve our previously reported limits and reflect the most sensitive broad-band search for untriggered and unmodeled gravitational wave bursts to date.
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“Upper Limits on a Stochastic Background of Gravitational Waves”, Physical Review Letters (2005).
B. Abbott, R. Abbott, Rana X. Adhikari, J. Agresti, and S. B. Anderson, et al.Abstract
The Laser Interferometer Gravitational-Wave Observatory has performed a third science run with much improved sensitivities of all three interferometers. We present an analysis of approximately 200 hours of data acquired during this run, used to search for a stochastic background of gravitational radiation. We place upper bounds on the energy density stored as gravitational radiation for three different spectral power laws. For the flat spectrum, our limit of Ω_0<8.4×10^(-4) in the 69–156 Hz band is ~10^5 times lower than the previous result in this frequency range.
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“Upper limits from the LIGO and TAMA detectors on the rate of gravitational-wave bursts”, Physical Review D (2005).
B. Abbott, R. Abbott, Rana X. Adhikari, A. Ageev, and J. Agresti, et al.Abstract
We report on the first joint search for gravitational waves by the TAMA and LIGO collaborations. We looked for millisecond-duration unmodeled gravitational-wave bursts in 473 hr of coincident data collected during early 2003. No candidate signals were found. We set an upper limit of 0.12 events per day on the rate of detectable gravitational-wave bursts, at 90% confidence level. From software simulations, we estimate that our detector network was sensitive to bursts with root-sum-square strain amplitude above approximately 1–3×10-19 Hz-1/2 in the frequency band 700-2000 Hz. We describe the details of this collaborative search, with particular emphasis on its advantages and disadvantages compared to searches by LIGO and TAMA separately using the same data. Benefits include a lower background and longer observation time, at some cost in sensitivity and bandwidth. We also demonstrate techniques for performing coincidence searches with a heterogeneous network of detectors with different noise spectra and orientations. These techniques include using coordinated software signal injections to estimate the network sensitivity, and tuning the analysis to maximize the sensitivity and the livetime, subject to constraints on the background.
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“Search for gravitational waves from primordial black hole binary coalescences in the galactic halo”, Physical Review D (2005).
B. Abbott, R. Abbott, Rana X. Adhikari, A. Ageev, and B. Allen, et al.Abstract
We use data from the second science run of the LIGO gravitational-wave detectors to search for the gravitational waves from primordial black hole binary coalescence with component masses in the range 0.2–1.0M☉. The analysis requires a signal to be found in the data from both LIGO observatories, according to a set of coincidence criteria. No inspiral signals were found. Assuming a spherical halo with core radius 5 kpc extending to 50 kpc containing nonspinning black holes with masses in the range 0.2–1.0M☉, we place an observational upper limit on the rate of primordial black hole coalescence of 63 per year per Milky Way halo (MWH) with 90% confidence.
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“Search for gravitational waves from galactic and extra-galactic binary neutron stars”, Physical Review D (2005).
B. P. Abbott, R. Abbott, Rana X. Adhikari, A. Ageev, and B. Allen, et al.Abstract
We use 373 hours (≈15 days) of data from the second science run of the LIGO gravitational-wave detectors to search for signals from binary neutron star coalescences within a maximum distance of about 1.5 Mpc, a volume of space which includes the Andromeda Galaxy and other galaxies of the Local Group of galaxies. This analysis requires a signal to be found in data from detectors at the two LIGO sites, according to a set of coincidence criteria. The background (accidental coincidence rate) is determined from the data and is used to judge the significance of event candidates. No inspiral gravitational-wave events were identified in our search. Using a population model which includes the Local Group, we establish an upper limit of less than 47 inspiral events per year per Milky Way equivalent galaxy with 90% confidence for nonspinning binary neutron star systems with component masses between 1 and 3M☉.
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“First all-sky upper limits from LIGO on the strength of periodic gravitational waves using the Hough transform”, Physical Review D (2005).
B. Abbott, Rana X. Adhikari, J. Agresti, S. B. Anderson, and M. Araya, et al.Abstract
We perform a wide parameter-space search for continuous gravitational waves over the whole sky and over a large range of values of the frequency and the first spin-down parameter. Our search method is based on the Hough transform, which is a semicoherent, computationally efficient, and robust pattern recognition technique. We apply this technique to data from the second science run of the LIGO detectors and our final results are all-sky upper limits on the strength of gravitational waves emitted by unknown isolated spinning neutron stars on a set of narrow frequency bands in the range 200–400 Hz. The best upper limit on the gravitational-wave strain amplitude that we obtain in this frequency range is 4.43×10^(-23).
2004
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“Setting upper limits on the strength of periodic gravitational waves from PSR J1939+2134 using the first science data from the GEO 600 and LIGO detectors”, Physical Review D (2004).
B. Abbott, R. Abbott, Rana X. Adhikari, A. Ageev, and B. Allen, et al.Abstract
Data collected by the GEO 600 and LIGO interferometric gravitational wave detectors during their first observational science run were searched for continuous gravitational waves from the pulsar J1939+2134 at twice its rotation frequency. Two independent analysis methods were used and are demonstrated in this paper: a frequency domain method and a time domain method. Both achieve consistent null results, placing new upper limits on the strength of the pulsar's gravitational wave emission. A model emission mechanism is used to interpret the limits as a constraint on the pulsar's equatorial ellipticity.
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“First upper limits from LIGO on gravitational wave bursts”, Physical Review D (2004).
B. Abbott, R. Abbott, Rana X. Adhikari, A. Ageev, and B. Allen, et al.Abstract
We report on a search for gravitational wave bursts using data from the first science run of the Laser Interferometer Gravitational Wave Observatory (LIGO) detectors. Our search focuses on bursts with durations ranging from 4 to 100 ms, and with significant power in the LIGO sensitivity band of 150 to 3000 Hz. We bound the rate for such detected bursts at less than 1.6 events per day at a 90% confidence level. This result is interpreted in terms of the detection efficiency for ad hoc waveforms (Gaussians and sine Gaussians) as a function of their root-sum-square strain h(rss); typical sensitivities lie in the range h(rss) ~10^(-19)-10^(-17) strain/√Hz, depending on the waveform. We discuss improvements in the search method that will be applied to future science data from LIGO and other gravitational wave detectors.
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“Analysis of LIGO data for gravitational waves from binary neutron stars”, Physical Review D (2004).
B. Abbott, R. Abbott, Rana X. Adhikari, A. Ageev, and B. Allen, et al.Abstract
We report on a search for gravitational waves from coalescing compact binary systems in the Milky Way and the Magellanic Clouds. The analysis uses data taken by two of the three LIGO interferometers during the first LIGO science run and illustrates a method of setting upper limits on inspiral event rates using interferometer data. The analysis pipeline is described with particular attention to data selection and coincidence between the two interferometers. We establish an observational upper limit of R<1.7x10^(2) per year per Milky Way Equivalent Galaxy (MWEG), with 90% confidence, on the coalescence rate of binary systems in which each component has a mass in the range 1-3 M☉.
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“Analysis of first LIGO science data for stochastic gravitational waves”, Physical Review D (2004).
B. Abbott, R. Abbott, Rana X. Adhikari, A. Ageev, and B. Allen, et al.Abstract
We present the analysis of between 50 and 100 h of coincident interferometric strain data used to search for and establish an upper limit on a stochastic background of gravitational radiation. These data come from the first LIGO science run, during which all three LIGO interferometers were operated over a 2-week period spanning August and September of 2002. The method of cross correlating the outputs of two interferometers is used for analysis. We describe in detail practical signal processing issues that arise when working with real data, and we establish an observational upper limit on a f^-3 power spectrum of gravitational waves. Our 90% confidence limit is Ω0h100(^2)<~23±4.6 in the frequency band 40–314 Hz, where h100 is the Hubble constant in units of 100 km/sec/Mpc and Ω0 is the gravitational wave energy density per logarithmic frequency interval in units of the closure density. This limit is approximately 104 times better than the previous, broadband direct limit using interferometric detectors, and nearly 3 times better than the best narrow-band bar detector limit. As LIGO and other worldwide detectors improve in sensitivity and attain their design goals, the analysis procedures described here should lead to stochastic background sensitivity levels of astrophysical interest.
2003
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“Feedforward reduction of the microseism disturbance in a long-base-line interferometric gravitational-wave detector”, Review of Scientific Instruments (2003).
J. A. Giaime, E. J. Daw, M. Weitz, Rana X. Adhikari, P. Fritschel, R. Abbott, R. Bork, and J. HeefnerAbstract
Standing ocean waves driven by storms can excite surface waves in the ocean floor at twice the wave frequency. These traverse large distances on land and are called the double-frequency (DF) microseism. The Laser Interferometer Gravitational-wave Observatory (LIGO) detector relies on length servos to maintain optical resonance in its 4 km Fabry–Pérot cavities, which consist of seismically isolated in-vacuum suspended test mass mirrors in three different buildings. Correcting for the DF microseism motion can require tens of micrometers of actuation, a significant fraction of the feedback dynamic range. The LIGO seismic isolation design provides an external fine actuation system (FAS), which allows long-range displacement of the optical tables that support the test mass suspensions. We report on a feedforward control system that uses seismometer signals from each building to produce correction signals, which are applied to the FAS, largely removing the microseism disturbance independently of length control servos. The root-mean-squared displacement from the microseism near 0.15 Hz can be reduced by 10 dB on average.
Full text · DOI: 10.1063/1.1524717
2000
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“Determination and optimization of mode matching into optical cavities by heterodyne detection”, Optics Letters (2000).
Guido Mueller, Qi-ze Shu, Rana X. Adhikari, D. B. Tanner, David Reitze, Daniel Sigg, Nergis Mavalvala, and Jordan CampAbstract
We report on a novel high-sensitivity method to characterize and improve mode matching into optical cavities. This method is based on heterodyne detection of cylindrical transverse cavity modes. A specially designed annular-segmented photodiode is used to measure the amplitude of nonresonant modes reflected by the cavity. Our measurements allow us to optimize cavity mode matching to nearly 99.98% and will play an important diagnostic role in gravitational-wave detectors.
Full text · DOI: 10.1364/ol.25.000266