Observation of Gravitational Waves from a Binary Black Hole Merger — TEI-tagged view

(2016date). “Observation of Gravitational Waves from a Binary Black Hole Merger.” Physical Review Letters / arXivtitle·j, PasadenaplaceName.

Object of study — Gravitational wavesterm·dom emitted by the mergerterm·key of two black holesterm·key.

Research question — Can the gravitational wavesterm·dom predicted by general relativityterm·dom be directly detected on Earth?

Contribution — Reports GW150914term, the first direct detection of gravitational wavesterm·dom, confirming a century-old prediction of general relativityterm·dom and opening gravitational-wave astronomy.

Full text — tagged

The reference list is not part of the text we hold for this paper. Our copy was extracted from the publisher's page and the bibliography did not survive that extraction, so the article below ends before its references. Nothing has been removed by us.

PRL 116, 061102 (2016) Selected for a Viewpoint in Physics P H Y S I C A L R E V I E W L E T T E R S week ending 12 FEBRUARY 2016 Observation of Gravitational Wavesterm·dom from a Binary Black Hole Mergerterm·dom B. P. Abbott et al.* (LIGOterm·key Scientific Collaboration and Virgo Collaboration) (Received 21 January 2016; published 11 February 2016) On September 14, 2015date at 09:50:45 UTC the two detectorsterm·key of the Laser Interferometerterm·dom Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signalterm·key. The signalterm·key sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strainterm of 1.0 × 10−21. It matches the waveformterm·key predicted by general relativityterm·dom for the inspiralterm·def and mergerterm·key of a pair of black holesterm·key and the ringdownterm·def of the resulting single black holeterm·key. The signalterm·key was observed with a matched-filter signal-to-noise ratioterm·var of 24 and a false alarm rate estimated to be less than 1 event per 203 000 years, equivalent to a significanceterm greater −180 Mpc corresponding to a redshift z = 0.09+0.03 than 5.1σ. The source lies at a luminosity distance of 410+160 −0.04 . In the source frame, the initial black holeterm·key masses are 36+5 −4 M⊙ and 29+4 −4 M⊙, and the final black holeterm·key mass is 62+4 −0.5 M⊙c2 radiated in gravitational wavesterm·dom. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black holeterm·key systems. This is the first direct detection of gravitational wavesterm·dom and the first observation of a binary black hole mergerterm·dom. −4 M⊙, with 3.0+0.5 DOI: 10.1103/PhysRevLett.116.061102 I. INTRODUCTION In 1916, the year after the final formulation of the field equations of general relativityterm·dom, Albert Einstein predicted the existence of gravitational wavesterm·dom. He found that the linearized weak-field equations had wave solutions: transverse waves of spatial strainterm that travel at the speed of light, generated by time variations of the mass quadrupole momentterm of the source [1,2]. Einstein understood that gravitational-wave amplitudes would be remarkably the Chapel Hill conference in small; moreover, until 1957 there was significant debate about the physical reality of gravitational wavesterm·dom [3]. Also in 1916, Schwarzschild published a solution for the field equations [4] that was later understood to describe a black holeterm·key [5,6], and in 1963 Kerr generalized the solution to rotating black holesterm·key [7]. Starting in the 1970s theoretical work led to the understanding of black holeterm·key quasinormal modes [8–10], and in the 1990s higher-order post- Newtonian calculations [11] preceded extensive analytical studies of relativistic two-body dynamics [12,13]. These advances, together with numerical relativityterm·key breakthroughs in the past decade [14–16], have enabled modeling of binary black hole mergersterm·dom and accurate predictions of their gravitationalterm·key waveformsterm·key. While numerous black holeterm·key candidates have now been identified through electromagnetic observations [17–19], black holeterm·key mergersterm·key have not previously been observed. *Full author list given at the end of the article. Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. The discovery of the binary pulsar system PSR B1913+16 by Hulse and Taylor [20] and subsequent observations of its energy loss by Taylor and Weisberg [21] demonstrated the existence of gravitational wavesterm·dom. This discovery, along with emerging astrophysical understanding [22], led to the recognition that direct observations of the amplitude and phase of gravitational wavesterm·dom would enable studies of additional relativistic systems and provide new tests of general relativityterm·dom, especially in the dynamic strong-field regime. Experiments to detect gravitational wavesterm·dom began with Weber and his resonant mass detectorsterm·key in the 1960s [23], followed by an international network of cryogenic resonant detectorsterm·key [24]. Interferometric detectorsterm·key were first suggested in the early 1960s [25] and the 1970s [26]. A study of the noise and performance of such detectorsterm·key [27], and further concepts to improve them [28], led to proposals for long-baseline broadband laser interferometersterm·dom with the potential for significantly increased sensitivity [29–32]. By the early 2000s, a set of initial detectorsterm·key was completed, including TAMA 300 in Japan, GEO 600 in Germany, the Laser Interferometerterm·dom Gravitational-Wave Observatory (LIGOterm·key) in the United States, and Virgo in Italy. Combinations of these detectorsterm·key made joint observations from 2002 through 2011, setting upper limits on a variety of gravitational-wave sources while evolving into a global network. In 2015date, Advanced LIGOterm·key became the first of a significantly more sensitive network of advanced detectorsterm·key to begin observations [33–36]. A century after the fundamental predictions of Einstein and Schwarzschild, we report the first direct detection of gravitational wavesterm·dom and the first direct observation of a binary black holeterm·key system merging to form a single black holeterm·key. Our observations provide unique access to the 0031-9007=16=116(6)=061102(16) 061102-1 Published by the American Physical Society PRL 116, 061102 (2016) P H Y S I C A L R E V I E W L E T T E R S week ending 12 FEBRUARY 2016 properties of space-time in the strong-field, high-velocity regime and confirm predictions of general relativityterm·dom for the nonlinear dynamics of highly disturbed black holesterm·key. II. OBSERVATION On September 14, 2015date at 09:50:45 UTC, the LIGOterm·key Hanford, WA, and Livingston, LA, observatories detected the coincident signalterm·key GW150914term shown in Fig. 1. The initial detection was made by low-latency searches for generic gravitational-wave transients [41] and was reported within three minutes of data acquisition [43]. Subsequently, matched-filter analyses that use relativistic models of compact binary waveformsterm·key [44] recovered GW150914term as the most significant event from each detectorterm·key for the observations reported here. Occurring within the 10-ms intersite FIG. 1. The gravitational-wave event GW150914term observed by the LIGOterm·key Hanford (H1, left column panels) and Livingston (L1, right column panels) detectorsterm·key. Times are shown relative to September 14, 2015date at 09:50:45 UTC. For visualization, all time series are filtered with a 35–350 Hz bandpass filter to suppress large fluctuations outside the detectorsterm·key’ most sensitive frequency band, and band-reject filters to remove the strong instrumental spectral lines seen in the Fig. 3 spectra. Top row, left: H1 strainterm·key. Top row, right: L1 strainterm·key. GW150914term arrived first at L1 and 6.9+0.5 −0.4 ms later at H1; for a visual comparison, the H1 data are also shown, shifted in time by this amount and inverted (to account for the detectorsterm·key’ relative orientations). Second row: Gravitational-wave strainterm projected onto each detectorterm·key in the 35–350 Hz band. Solid lines show a numerical relativityterm·key waveformterm·key for a system with parameters consistent with those recovered from GW150914term [37,38] confirmed to 99.9% by an independent calculation based on [15]. Shaded areas show 90% credible regions for two independent waveformterm·key reconstructions. One (dark gray) models the signalterm·key using binary black holeterm·key template waveformsterm·key [39]. The other (light gray) does not use an astrophysical model, but instead calculates the strainterm·key signalterm·key as a linear combination of sine-Gaussian wavelets [40,41]. These reconstructions have a 94% overlap, as shown in [39]. Third row: Residuals after subtracting the filtered numerical relativityterm·key waveformterm·key from the filtered detectorterm·key time series. Bottom row:A time-frequency representation [42] of the strainterm·key data, showing the signalterm·key frequency increasing over time. 061102-2 PRL 116, 061102 (2016) P H Y S I C A L R E V I E W L E T T E R S week ending 12 FEBRUARY 2016 propagation time, the events have a combined signal-tonoise ratio (SNR) of 24 [45]. Only the LIGOterm·key detectorsterm·key were observing at the time of GW150914term. The Virgo detectorterm·key was being upgraded, and GEO 600, though not sufficiently sensitive to detect this event, was operating but not in observational mode. With only two detectorsterm·key the source position is primarily determined by the relative arrival time and localized to an area of approximately 600 deg2 (90% credible region) [39,46]. The basic features of GW150914term point to it being produced by the coalescence of two black holesterm—i.e., their orbital inspiralterm and mergerterm·key, and subsequent final black hole ringdownterm. Over 0.2 s, the signalterm·key increases in frequency and amplitude in about 8 cycles from 35 to 150 Hz, where the amplitude reaches a maximum. The most plausible explanation for this evolution is the inspiralterm·def of two orbiting masses, m1 and m2, due to gravitational-wave emission. At the lower frequencies, such evolution is characterized by the chirp massterm [11] M ¼ ðm1m2Þ3=5 ðm1 þ m2Þ1=5 ¼ c3 G (cid:1) 5 96 π−8=3f−11=3 _f (cid:3) 3=5 ; where f and _f are the observed frequency and its time derivative and G and c are the gravitationalterm·key constant and speed of light. Estimating f and _f from the data in Fig. 1, we obtain a chirp massterm of M ≃ 30M⊙, implying that the total mass M ¼ m1 þ m2 is ≳70M⊙ in the detectorterm·key frame. This bounds the sum of the Schwarzschild radii of the binary components to 2GM=c2 ≳ 210 km. To reach an orbital frequency of 75 Hz (half the gravitational-wave frequency) the objects must have been very close and very compact; equal Newtonian point masses orbiting at this frequency would be only ≃350 km apart. A pair of neutron stars, while compact, would not have the required mass, while a black holeterm·key neutron star binary with the deduced chirp massterm would have a very large total mass, and would thus merge at much lower frequency. This leaves black holesterm·key as the only known objects compact enough to reach an orbital frequency of 75 Hz without contact. Furthermore, the decay of the waveformterm·key after it peaks is consistent with the damped oscillations of a black holeterm·key relaxing to a final stationary Kerr configuration. Below, we present a general-relativistic analysis of GW150914term; Fig. 2 shows the calculated waveformterm·key using the resulting source parameters. III. DETECTORSterm·key Gravitational-wave astronomy exploits multiple, widely separated detectorsterm·key to distinguish gravitational wavesterm·dom from local to provide source sky localization, and to measure wave polarizations. The LIGOterm·key sites each operate a single Advanced LIGOterm·key instrumental and environmental noise, FIG. 2. Top: Estimated gravitational-wave strainterm amplitude from GW150914term projected onto H1. This shows the full bandwidth of the waveformsterm·key, without the filtering used for Fig. 1. The inset images show numerical relativityterm·key models of the black holeterm·key horizons as the black holesterm·key coalesce. Bottom: The Keplerian effective black holeterm·key separation in units of Schwarzschild radii (RS = 2GM=c2) and the effective relative velocity given by the post-Newtonian parameter v=c ¼ ðGMπf=c3Þ1=3, where f is the gravitational-wave frequency calculated with numerical relativityterm·key and M is the total mass (value from Table I). detectorterm·key [33], a modified Michelson interferometerterm (see Fig. 3) that measures gravitational-wave strainterm as a difference in length of its orthogonal arms. Each arm is formed by two mirrors, acting as test masses, separated by Lx ¼ Ly ¼ L = 4 km. A passing gravitational waveterm·dom effectively alters the arm lengths such that the measured difference is ΔLðtÞ ¼ δLx − δLy ¼ hðtÞL, where h is the gravitational-wave strainterm amplitude projected onto the detectorterm·key. This differential length variation alters the phase difference between the two light fields returning to the beam splitter, transmitting an optical signalterm·key proportional to the gravitational-wave strainterm to the output photodetector. To achieve sufficient sensitivity to measure gravitational wavesterm·dom, the detectorsterm·key include several enhancements to the basic Michelson interferometerterm·dom. First, each arm contains a resonant optical cavityterm, formed by its two test mass mirrors, that multiplies the effect of a gravitational waveterm·dom on the light phase by a factor of 300 [48]. Second, a partially transmissive power-recycling mirrorterm at the input provides additional resonant buildup of the laser light in the interferometerterm·dom as a whole [49,50]: 20 W of laser input is increased to 700 W incident on the beam splitter, which is further increased to 100 kW circulating in each arm cavity. Third, a partially transmissive signal-recycling mirror at the output optimizes 061102-3 PRL 116, 061102 (2016) P H Y S I C A L R E V I E W L E T T E R S week ending 12 FEBRUARY 2016 (b) (a) FIG. 3. Simplified diagram of an Advanced LIGOterm·key detectorterm·key (not to scale). A gravitational waveterm·dom propagating orthogonally to the detectorterm·key plane and linearly polarized parallel to the 4-km optical cavities will have the effect of lengthening one 4-km arm and shortening the other during one half-cycle of the wave; these length changes are reversed during the other half-cycle. The output photodetector records these differential cavity length variations. While a detectorterm·key’s directional response is maximal for this case, it is still significant for most other angles of incidence or polarizations (gravitational wavesterm·dom propagate freely through the Earth). Inset (a): Location and orientation of the LIGOterm·key detectorsterm·key at Hanford, WA (H1) and Livingston, LA (L1). Inset (b): The instrument noise for each detectorterm·key near the time of the signalterm·key detection; this is an amplitude spectral density, expressed in terms of equivalent gravitational-wave strainterm amplitude. The sensitivity is limited by photon shot noise at frequencies above 150 Hz, and by a superposition of other noise sources at lower frequencies [47]. Narrow-band features include calibration lines (33–38, 330, and 1080 Hz), vibrational modes of suspension fibers (500 Hz and harmonics), and 60 Hz electric power grid harmonics. the gravitational-wave signalterm·key extraction by broadening the bandwidth of the arm cavities [51,52]. The interferometerterm·dom is illuminated with a 1064-nm wavelength Nd:YAG laser, stabilized in amplitude, frequency, and beam geometry [53,54]. The gravitational-wave signalterm·key is extracted at the output port using a homodyne readout [55]. These interferometry techniques are designed to maximize the conversion of strainterm·key to optical signalterm·key, thereby minimizing the impact of photon shot noise (the principal noise at high frequencies). High strain sensitivityterm also requires that the test masses have low displacement noise, which is achieved by isolating them from seismic noise (low frequencies) and designing them to have low thermal noise (intermediate frequencies). Each test mass is suspended as the final stage of a quadruple-pendulum system [56], supported by an active seismic isolation platform [57]. These systems collectively provide more than 10 orders of magnitude of isolation from ground motion for frequencies above 10 Hz. Thermal noise is minimized by using low-mechanical-loss materials in the test masses and their suspensions: the test masses are 40-kg fused silica substrates with low-loss dielectric optical coatings [58,59], and are suspended with fused silica fibers from the stage above [60]. To minimize additional noise sources, all components other than the laser source are mounted on vibration isolation stages in ultrahigh vacuum. To reduce optical phase fluctuations caused by Rayleigh scattering, the pressure in the 1.2-m diameter tubes containing the armcavity beams is maintained below 1 μPa. Servo controls are used to hold the arm cavities on resonance [61] and maintain proper alignment of the optical components [62]. The detectorterm·key output is calibrated in strainterm·key by measuring its response to test mass motion induced by photon pressure from a modulated calibration laser beam [63]. The calibration is established to an uncertainty (1σ) of less than 10% in amplitude and 10 degrees in phase, and is continuously monitored with calibration laser excitations at selected frequencies. Two alternative methods are used to validate the absolute calibration, one referenced to the main laser wavelength and the other to a radio-frequency oscillator 061102-4 PRL 116, 061102 (2016) P H Y S I C A L R E V I E W L E T T E R S week ending 12 FEBRUARY 2016 [64]. Additionally, the detectorterm·key response to gravitational wavesterm·dom is tested by injecting simulated waveformsterm·key with the calibration laser. To monitor environmental disturbances and their influence on the detectorsterm·key, each observatory site is equipped with an array of sensors: seismometers, accelerometers, radio receivers, weather microphones, magnetometers, sensors, ac-power line monitors, and a cosmic-ray detectorterm·key [65]. Another ∼105 channels record the interferometerterm·dom’s operating point and the state of the control systems. Data collection is synchronized to Global Positioning System (GPS) time to better than 10 μs [66]. Timing accuracy is verified with an atomic clock and a secondary GPS receiver at each observatory site. In their most sensitive band, 100–300 Hz, the current LIGOterm·key detectorsterm·key are 3 to 5 times more sensitive to strainterm·key than initial LIGOterm·key [67]; at lower frequencies, the improvement is even greater, with more than ten times better sensitivity below 60 Hz. Because the detectorsterm·key respond proportionally to gravitational-wave amplitude, at low redshift the volume of spaceterm to which they are sensitive increases as the cube of strain sensitivityterm. For binary black holesterm·key with masses similar to GW150914term, the space-time volume surveyed by the observations reported here surpasses previous observations by an order of magnitude [68]. IV. DETECTORterm·key VALIDATION Both detectorsterm·key were in steady state operation for several hours around GW150914term. All performance measures, in particular their average sensitivity and transient noise behavior, were typical of the full analysis period [69,70]. Exhaustive investigations of instrumental and environmental disturbances were performed, giving no evidence to suggest that GW150914term could be an instrumental artifact [69]. The detectorsterm·key’ susceptibility to environmental disturbances was quantified by measuring their response to specially generated magnetic, radio-frequency, acoustic, and vibration excitations. These tests indicated that any external disturbance large enough to have caused the observed signalterm·key would have been clearly recorded by the array of environmental sensors. None of the environmental sensors recorded any disturbances that evolved in time and frequency like GW150914term, and all environmental fluctuations during the second that contained GW150914term were too small to account for more than 6% of its strainterm·key amplitude. Special care was taken to search for long-range correlated disturbances that might produce nearly simultaneous signalsterm·key at the two sites. No significant disturbances were found. The detectorterm·key strainterm·key data exhibit non-Gaussian noise transients that arise from a variety of instrumental mechanisms. Many have distinct signatures, visible in auxiliary data channels that are not sensitive to gravitational wavesterm·dom; such instrumental transients are removed from our analyses [69]. Any instrumental transients that remain in the data are accounted for in the estimated detectorterm·key backgrounds described below. There is no evidence for instrumental transients that are temporally correlated between the two detectorsterm·key. V. SEARCHES We present the analysis of 16 days of coincident observations between the two LIGOterm·key detectorsterm·key from September 12 to October 20, 2015date. This is a subset of the data from Advanced LIGOterm·key’s first observational period that ended on January 12, 2016. GW150914term is confidently detected by two different types of searches. One aims to recover signalsterm·key from the coalescence of compact objects, using optimal matched filteringterm·mth with waveformsterm·key predicted by general relativityterm·dom. The other search targets a broad range of generic transient signalsterm·key, with minimal assumptions about waveformsterm·key. These searches use independent methods, and their response to detector noiseterm consists of different, uncorrelated, events. However, strong signalsterm·key from binary black hole mergersterm·dom are expected to be detected by both searches. Each search identifies candidate eventsterm that are detected at both observatories consistent with the intersite propagation time. Events are assigned a detection-statisticterm value that ranks their likelihood of being a gravitational-wave signalterm·key. The significanceterm of a candidate eventterm is determined by the search backgroundterm—the rate at which detector noiseterm produces events with a detection-statisticterm value equal to or higher than the candidate eventterm. Estimating this background is challenging for two reasons: the detector noiseterm is nonstationary and non-Gaussian, so its properties must be empirically determined; and it is not possible to shield the detectorterm·key from gravitational wavesterm·dom to directly measure a signal-free background. The specific procedure used to estimate the background is slightly different for the two searches, but both use a time-shift techniqueterm·mth: the time stamps of one detectorterm·key’s data are artificially shifted by an offset that is large compared to the intersite propagation time, and a new set of events is produced based on this time-shifted data set. For instrumental noise that is uncorrelated between detectorsterm·key this is an effective way to estimate the background. In this process a gravitationalwave signalterm·key in one detectorterm·key may coincide with time-shifted noise transients in the other detectorterm·key, thereby contributing to the background estimate. This leads to an overestimate of the noise backgroundterm and therefore to a more conservative assessment of the significanceterm of candidate eventsterm. The characteristics of non-Gaussian noise vary between different time-frequency regions. This means that the search backgroundsterm are not uniform across the space of signalsterm·key being searched. To maximize sensitivity and provide a better estimate of event significanceterm, the searches sort both their background estimates and their event candidates into different classes according to their time-frequency morphology. The significanceterm of a candidate eventterm is measured against the background of its class. To account for having searched 061102-5 PRL 116, 061102 (2016) P H Y S I C A L R E V I E W L E T T E R S week ending 12 FEBRUARY 2016 multiple classes, this significanceterm is decreased by a trials factor equal to the number of classes [71]. A. Generic transient searchterm Designed to operate without a specific waveformterm·key model, this search identifies coincident excess power in timethe detectorterm·key strainterm·key data frequency representations of [43,72], for signalterm·key frequencies up to 1 kHz and durations up to a few seconds. is p ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2Ec=ð1 þ En=EcÞ The search reconstructs signalterm·key waveformsterm·key consistent with a common gravitational-wave signalterm·key in both detectorsterm·key using a multidetector maximum likelihood method. Each ranked according to the detection statisticterm event ηc ¼ , where Ec is the dimensionless coherent signalterm·key energy obtained by cross-correlating the two reconstructed waveformsterm·key, and En is the dimensionless residual noise energy after the reconstructed signalterm·key is subtracted from the data. The statistic ηc thus quantifies the SNR of the event and the consistency of the data between the two detectorsterm·key. Based on their time-frequency morphology, the events are divided into three mutually exclusive search classes, as described in [41]: events with time-frequency morphology of known populations of noise transients (class C1), events with frequency that increases with time (class C3), and all remaining events (class C2). Detected with ηc = 20.0, GW150914term is the strongest event of the entire search. Consistent with its coalescence signalterm·key signature, it is found in the search class C3 of events with increasing time-frequency evolution. Measured on a background equivalent to over 67 400 years of data and including a trials factor of 3 to account for the search classes, its false alarm rate is lower than 1 in 22 500 years. This corresponds to a probability < 2 × 10−6 of observing one or more noise events as strong as GW150914term during the analysis time, equivalent to 4.6σ. The left panel of Fig. 4 shows the C3 class results and background. The selection criteria that define the search class C3 reduce the background by introducing a constraint on the signalterm·key morphology. In order to illustrate the significanceterm of GW150914term against a background of events with arbitrary shapes, we also show the results of a search that uses the same set of events as the one described above but without this constraint. Specifically, we use only two search classes: the C1 class and the union of C2 and C3 classes (C2 þ C3). In this two-class search the GW150914term event is found in the C2 þ C3 class. The left panel of Fig. 4 shows the C2 þ C3 class results and background. In the background of this class there are four events with ηc ≥ 32.1, yielding a false alarm rate for GW150914term of 1 in 8 400 years. This corresponds to a false alarm probability of 5 × 10−6 equivalent to 4.4σ. FIG. 4. Search results from the generic transient searchterm (left) and the binary coalescence searchterm (right). These histograms show the number of candidate eventsterm (orange markers) and the mean number of background events (black lines) in the search class where GW150914term was found as a function of the search detection statisticterm and with a bin width of 0.2. The scales on the top give the significanceterm of an event in Gaussian standard deviationsterm·stat based on the corresponding noise background. The significanceterm of GW150914term is greater than 5.1σ and 4.6σ for the binary coalescence and the generic transient searchesterm, respectively. Left: Along with the primary search (C3) we also show the results (blue markers) and background (green curve) for an alternative search that treats events independently of their frequency evolution (C2 þ C3). The classes C2 and C3 are defined in the text. Right: The tail in the black-line background of the binary coalescence searchterm is due to random coincidences of GW150914term in one detectorterm·key with noise in the other detectorterm·key. (This type of event is practically absent in the generic transient searchterm background because they do not pass the time-frequency consistency requirements used in that search.) The purple curve is the background excluding those coincidences, which is used to assess the significanceterm of the second strongest event. 061102-6 PRL 116, 061102 (2016) P H Y S I C A L R E V I E W L E T T E R S week ending 12 FEBRUARY 2016 For robustness and validation, we also use other generic transient searchterm algorithms [41]. A different search [73] and a parameter estimation follow-up [74] detected GW150914term with consistent significanceterm and signalterm·key parameters. B. Binary coalescence searchterm TABLE I. Source parameters for GW150914term. We report median values with 90% credible intervals that include statistical errors, and systematic errors from averaging the results of different waveformterm·key models. Masses are given in the source to the detectorterm·key frame multiply by (1 þ z) frame; [90]. The source redshift assumes standard cosmology [91]. to convert results This search targets gravitational-wave emission from binary systems with individual masses from 1 to 99M⊙, total mass less than 100M⊙, and dimensionless spins up to 0.99 [44]. To model systems with total mass larger than 4M⊙, we use the effective-one-body formalismterm [75], which combines from the post-Newtonian approach [11,76] with results from black holeterm·key perturbation theory and numerical relativityterm·key. The waveformterm·key model [77,78] assumes that the spins of the merging objects are aligned with the orbital angular momentum, but the resulting templates can, nonetheless, effectively recover systems with misaligned spins region of GW150914term [44]. Approximately 250 000 template waveformsterm·key are used to cover this parameter space. in the parameter The search calculates the matched-filter signal-to-noise ratioterm·var ρðtÞ for each template in each detectorterm·key and identifies maxima of ρðtÞ with respect to the time of arrival of the signalterm·key [79–81]. For each maximum we calculate a chi-squaredterm·stat statistic χ2 to test whether the data in several different r frequency bands are consistent with the matching template [82]. Values of χ2 r near unity indicate that the signalterm·key is consistent with a coalescence. If χ2 r is greater than unity, ρðtÞ is reweighted as ˆρ ¼ ρ=f½1 þ ðχ2 rÞ3(cid:2)=2g1=6 [83,84]. The final step enforces coincidence between detectorsterm·key by selecting event pairs that occur within a 15-ms window and come from the same template. The 15-ms window is determined by the 10-ms intersite propagation time plus 5 ms for uncertainty in arrival time of weak signalsterm·key. We rank coincident events based on the quadrature sum ˆρc of the ˆρ from both detectorsterm·key [45]. To produce background data for this search the SNR maxima of one detectorterm·key are time shifted and a new set of coincident events is computed. Repeating this procedure ∼107 times produces a noise background analysis time equivalent to 608 000 years. To account for the search backgroundterm noise varying across the target signalterm·key space, candidate and background events are divided into three search classes based on template length. The right panel of Fig. 4 shows the background for the search class of GW150914term. The GW150914term detectionstatisticterm value of ˆρc = 23.6 is larger than any background event, so only an upper bound can be placed on its false alarm rate. Across the three search classes this bound is 1 in 203 000 years. This translates to a false alarm probability < 2 × 10−7, corresponding to 5.1σ. A second, independent matched-filter analysis that uses a different method for estimating the significanceterm of its events [85,86], also detected GW150914term with identical signalterm·key parameters and consistent significanceterm. Primary black holeterm·key mass Secondary black holeterm·key mass Final black holeterm·key mass Final black holeterm·key spin Luminosity distance Source redshift z −4 M⊙ −4 M⊙ −4 M⊙ 36+5 29+4 62+4 0.67+0.05 −0.07 410+160 −180 Mpc 0.09+0.03 −0.04 When an event is confidently identified as a real gravitational-wave signalterm·key, as for GW150914term, the background used to determine the significanceterm of other events is reestimated without the contribution of this event. This is the background distribution shown as a purple line in the right panel of Fig. 4. Based on this, the second most significant event has a false alarm rate of 1 per 2.3 years and corresponding Poissonian false alarm probability of 0.02. Waveformterm·key analysis of this event is indicates that astrophysical is also a binary black hole mergerterm·dom [44]. in origin it if it VI. SOURCE DISCUSSION The matched-filter search is optimized for detecting it provides only approximate estimates of signalsterm·key, but the source parameters. To refine them we use general relativity-based models [77,78,87,88], some of which include spin precession, and for each model perform a coherent Bayesianterm·stat analysis to derive posterior distributionsterm of the source parameters [89]. The initial and final masses, final spin, distance, and redshift of the source are shown in Table I. The spin of the primary black holeterm·key is constrained to be < 0.7 (90% credible interval) indicating it is not maximally spinning, while the spin of the secondary is only weakly constrained. These source parameters are discussed in detail in [39]. The parameter uncertainties include statistical errors and systematic errors from averaging the results of different waveformterm·key models. Using the fits to numerical simulations of binary black hole mergersterm·dom in [92,93], we provide estimates of the mass and spin of the final black holeterm·key, the total energy radiated in gravitational wavesterm·dom, and the peak gravitational-wave luminosity [39]. The estimated total energy radiated in gravitational wavesterm·dom is 3.0+0.5 −0.5 M⊙c2. The system reached a peak gravitational-wave luminosity of 3.6+0.5 −0.4 × 1056 erg=s, equivalent to 200+30 −20 M⊙c2=s. Several analyses have been performed to determine whether or not GW150914term is consistent with a binary 061102-7 PRL 116, 061102 (2016) P H Y S I C A L R E V I E W L E T T E R S week ending 12 FEBRUARY 2016 black holeterm·key system in general relativityterm·dom [94]. A first consistency check involves the mass and spin of the final black holeterm·key. In general relativityterm·dom, the end product of a black hole binary coalescenceterm is a Kerr black holeterm, which is fully described by its mass and spin. For quasicircular inspiralsterm·def, these are predicted uniquely by Einstein’s equations as a function of the masses and spins of the two progenitor black holesterm·key. Using fitting formulas calibrated to numerical relativityterm·key simulations [92], we verified that the remnant mass and spin deduced from the early stage of the coalescence and those inferred independently from the late stage are consistent with each other, with no evidence for disagreement from general relativityterm·dom. Within the post-Newtonian formalism, the phase of the gravitationalterm·key waveformterm·key during the inspiralterm·def can be expressed as a power series in f1=3. The coefficients of this expansion can be computed in general relativityterm·dom. Thus, we can test for consistency with general relativityterm·dom [95,96] by allowing the coefficients to deviate from the nominal values, and seeing if the resulting waveformterm·key is consistent with the data. In this second check [94] we place constraints on these deviations, finding no evidence for violations of general relativityterm·dom. Finally, assuming a modified dispersion relation for gravitational wavesterm·dom [97], our observations constrain the Compton wavelength of the graviton to be λg > 1013 km, which could be interpreted as a bound on the graviton mass mg < 1.2 × 10−22 eV=c2. This improves on Solar System and binary pulsar bounds [98,99] by factors of a few and a thousand, respectively, but does not improve on the modeldependent bounds derived from the dynamics of Galaxy clusters [100] and weak lensing observations [101]. In summary, all three tests are consistent with the predictions of general relativityterm·dom in the strong-field regime of gravity. GW150914term demonstrates the existence of stellar-mass black holesterm·key more massive than ≃25M⊙, and establishes that binary black holesterm·key can form in nature and merge within a Hubble time. Binary black holesterm·key have been predicted to form both in isolated binaries [102–104] and in dense environments by dynamical interactions [105–107]. The formation of such massive black holesterm·key from stellar evolution requires weak massive-star winds, which are possible in stellar environments with metallicity lower than ≃1=2 the solar value [108,109]. Further astrophysical implications of this binary black holeterm·key discovery are discussed in [110]. These observational results constrain the rate of stellarmass binary black hole mergersterm·dom in the local universe. Using several different models of the underlying binary black holeterm·key mass distribution, we obtain rate estimates ranging from 2–400 Gpc−3 yr−1 in the comoving frame [111–113]. This is consistent with a broad range of rate predictions as reviewed in [114], with only the lowest event rates being excluded. Binary black holeterm·key systems at larger distances contribute to a stochastic background of gravitational wavesterm from the superposition of unresolved systems. Predictions for such a background are presented in [115]. If the signalterm·key from such a population were detected, it would provide information about the evolution of such binary systems over the history of the universe. VII. OUTLOOK Further details about these results and associated data releases are available at [116]. Analysis results for the entire first observational period will be reported in future publications. Efforts are under way to enhance significantly the global gravitational-wave detectorterm·key network [117]. These include further commissioning of the Advanced LIGOterm·key detectorsterm·key to reach design sensitivity, which will allow detection of binaries like GW150914term with 3 times higher SNR. Additionally, Advanced Virgo, KAGRA, and a possible third LIGOterm·key detectorterm·key in India [118] will extend the network and significantly improve the position reconstruction and parameter estimation of sources. VIII. CONCLUSION The LIGOterm·key detectorsterm·key have observed gravitational wavesterm·dom from the mergerterm·key of two stellar-mass black holesterm·key. The detected waveformterm·key matches the predictions of general relativityterm·dom for the inspiralterm·def and mergerterm·key of a pair of black holesterm·key and the ringdownterm·def of the resulting single black holeterm·key. These observations demonstrate the existence of binary stellar-mass black holeterm·key systems. This is the first direct detection of gravitational wavesterm·dom and the first observation of a binary black hole mergerterm·dom. ACKNOWLEDGMENTS (STFC) of The authors gratefully acknowledge the support of the United States National Science Foundation (NSF) for the construction and operation of the LIGOterm·key Laboratory and Advanced LIGOterm·key as well as the Science and the United Technology Facilities Council Kingdom, the Max-Planck Society (MPS), and the State of Niedersachsen, Germany, for support of the construction of Advanced LIGOterm·key and construction and operation of the GEO 600 detectorterm·key. Additional support for Advanced LIGOterm·key was provided by the Australian Research Council. The authors gratefully acknowledge Italian Istituto Nazionale di Fisica Nucleare (INFN), the French Centre National de la Recherche Scientifique (CNRS), and the Foundation for Fundamental Research on Matter supported by the Netherlands Organisation for Scientific Research, for the construction and operation of the Virgo detectorterm·key, and for the creation and support of the EGO consortium. The authors also gratefully acknowledge research support from these agencies as well as by the Council of Scientific and Industrial Research of India, Department of Science and the 061102-8 PRL 116, 061102 (2016) P H Y S I C A L R E V I E W L E T T E R S week ending 12 FEBRUARY 2016 the the (LIO), Conselleria the Royal Society, Spanish Ministerio de Economía d’Economia the Govern de les Illes Balears, Technology, India, Science & Engineering Research Board (SERB), India, Ministry of Human Resource Development, y India, Competitividad, i Competitivitat and Conselleria d’Educació, Cultura i Universitats of the the European National Science Centre of Poland, Commission, the Scottish Funding Council, the Scottish Universities Physics Alliance, the Hungarian Scientific Research Fund (OTKA), the Lyon the National Research Institute of Origins Foundation of Korea, Industry Canada and the Province of Ontario through the Ministry of Economic Development and Innovation, the Natural Sciences and Engineering Research Council of Canada, Canadian Institute for Advanced Research, the Brazilian Ministry of Science, Technology, and Innovation, Russian Foundation for Basic Research, the Leverhulme Trust, the Research Corporation, Ministry of Science and Technology (MOST), Taiwan, and the Kavli Foundation. The authors gratefully acknowledge the support of the NSF, STFC, MPS, INFN, CNRS and the State of Niedersachsen, Germany, for provision of computational resources. This article has been assigned the document numbers LIGO-P150914 and VIR-0015A-16. [1] A. Einstein, Sitzungsber. K. Preuss. Akad. Wiss. 1, 688 (1916). [2] A. Einstein, Sitzungsber. K. Preuss. Akad. Wiss. 1, 154 (1918). [3] P. R. Saulson, Gen. Relativ. Gravit. 43, 3289 (2011). [4] K. Schwarzschild, Sitzungsber. K. Preuss. Akad. Wiss. 1, 189 (1916). [5] D. Finkelstein, Phys. Rev. 110, 965 (1958). [6] M. D. Kruskal, Phys. Rev. 119, 1743 (1960). [7] R. P. Kerr, Phys. Rev. Lett. 11, 237 (1963). [8] C. V. Vishveshwara, Nature (London) 227, 936 (1970). [9] W. H. Press, Astrophys. J. 170, L105 (1971). [10] S. Chandrasekhar and S. L. Detweiler, Proc. R. Soc. A 344, 441 (1975). [11] L. Blanchet, T. Damour, B. R. Iyer, C. M. Will, and A. G. Wiseman, Phys. Rev. Lett. 74, 3515 (1995). [12] L. Blanchet, Living Rev. Relativityterm·key 17, 2 (2014). [13] A. Buonanno and T. Damour, Phys. Rev. D 59, 084006 (1999). [14] F. Pretorius, Phys. Rev. Lett. 95, 121101 (2005). [15] M. Campanelli, C. O. Lousto, P. Marronetti, and Y. Zlochower, Phys. Rev. Lett. 96, 111101 (2006). [21] J. H. Taylor and J. M. Weisberg, Astrophys. J. 253, 908 (1982). [22] W. Press and K. Thorne, Annu. Rev. Astron. Astrophys. 10, 335 (1972). [23] J. Weber, Phys. Rev. 117, 306 (1960). [24] P. Astone et al., Phys. Rev. D 82, 022003 (2010). [25] M. E. Gertsenshtein and V. I. Pustovoit, Sov. Phys. JETP 16, 433 (1962). [26] G. E. Moss, L. R. Miller, and R. L. Forward, Appl. Opt. 10, 2495 (1971). [27] R. Weiss, Electromagnetically coupled broadband gravitationalterm·key antenna, Quarterly Report of the Research Laboratory for Electronics, MIT Report No. 105, 1972, https:// dcc.ligoterm·key.org/LIGOterm·key‑P720002/public/main. [28] R. W. P. Drever, in Gravitationalterm·key Radiation, edited by N. Deruelle and T. Piran (North-Holland, Amsterdam, 1983), p. 321. [29] R. W. P. Drever, F. J. Raab, K. S. Thorne, R. Vogt, and R. Weiss, Laser Interferometerterm·dom Gravitational-wave Observatory (LIGOterm·key) Technical Report, 1989, https://dcc.ligoterm·key.org/ LIGOterm·key‑M890001/public/main. [30] A. Abramovici et al., Science 256, 325 (1992). [31] A. Brillet, A. Giazotto et al., Virgo Project Technical Report No. VIR-0517A-15, 1989, https://tds.ego‑gw.it/ql/? c=11247. [32] J. Hough et al., Proposal for a joint German-British interferometric gravitational waveterm·dom detectorterm·key, MPQ Technical Report 147, No. GWD/137/JH(89), 1989, http://eprints .gla.ac.uk/114852. [33] J. Aasi et al., Classical Quantum Gravity 32, 074001 (2015date). [34] F. Acernese et al., Classical Quantum Gravity 32, 024001 (2015date). [35] C. Affeldt et al., Classical Quantum Gravity 31, 224002 (2014). [36] Y. Aso, Y. Michimura, K. Somiya, M. Ando, O. Miyakawa, T. Sekiguchi, D. Tatsumi, and H. Yamamoto, Phys. Rev. D 88, 043007 (2013). [37] The waveformterm·key shown is SXS:BBH:0305, available for download at http://www.black‑holes.org/waveformsterm·key. [38] A. H. Mroué et al., Phys. Rev. Lett. 111, 241104 (2013). [39] B. Abbott et al., arXiv:1602.03840. [40] N. J. Cornish and T. B. Littenberg, Classical Quantum Gravity 32, 135012 (2015date). [41] B. Abbott et al., arXiv:1602.03843. [42] S. Chatterji, L. Blackburn, G. Martin, and E. Katsavounidis, Classical Quantum Gravity 21, S1809 (2004). [43] S. Klimenko et al., Phys. Rev. D 93, 042004 (2016). [44] B. Abbott et al., arXiv:1602.03839. [45] S. A. Usman et al., arXiv:1508.02357. [46] B. Abbott et al., https://dcc.ligoterm·key.org/LIGOterm·key‑P1500227/ [16] J. G. Baker, J. Centrella, D.-I. Choi, M. Koppitz, and J. van public/main. Meter, Phys. Rev. Lett. 96, 111102 (2006). [17] B. L. Webster and P. Murdin, Nature (London) 235, 37 (1972). [18] C. T. Bolton, Nature (London) 240, 124 (1972). [19] J. Casares and P. G. Jonker, Space Sci. Rev. 183, 223 (2014). [20] R. A. Hulse and J. H. Taylor, Astrophys. J. 195, L51 (1975). [47] B. Abbott et al., arXiv:1602.03838. [48] R. W. P. Drever, The Detection of Gravitational Wavesterm·dom, (Cambridge University Press, edited by D. G. Blair Cambridge, England, 1991). [49] R. W. P. Drever et al., in Quantum Optics, Experimental Gravity, and Measurement Theory, edited by P. Meystre and M. O. Scully, NATO ASI, Ser. B, Vol. 94 (Plenum Press, New York, 1983), pp. 503–514. 061102-9 PRL 116, 061102 (2016) P H Y S I C A L R E V I E W L E T T E R S week ending 12 FEBRUARY 2016 [50] R. Schilling (unpublished). [51] B. J. Meers, Phys. Rev. D 38, 2317 (1988). [52] J. Mizuno, K. A. Strainterm·key, P. G. Nelson, J. M. Chen, R. Schilling, A. Rüdiger, W. Winkler, and K. Danzmann, Phys. Lett. A 175, 273 (1993). [53] P. Kwee et al., Opt. Express 20, 10617 (2012). [54] C. L. Mueller et al., Rev. Sci. Instrum. 87, 014502 (2016). [55] T. T. Fricke et al., Classical Quantum Gravity 29, 065005 (2012). [56] S. M. Aston et al., Classical Quantum Gravity 29, 235004 (2012). [57] F. Matichard et al., Classical Quantum Gravity 32, 185003 (2015date). [58] G. M. Harry et al., Classical Quantum Gravity 24, 405 (2007). [59] M. Granata et al., Phys. Rev. D 93, 012007 (2016). [60] A. V. Cumming et al., Classical Quantum Gravity 29, 035003 (2012). [61] A. Staley et al., Classical Quantum Gravity 31, 245010 (2014). [62] L. Barsotti, M. Evans, and P. Fritschel, Classical Quantum Gravity 27, 084026 (2010). [63] B. Abbott et al., arXiv:1602.03845. [64] E. Goetz et al., in Gravitational Wavesterm·dom: Proceedings, of the 8th Edoardo Amaldi Conference, Amaldi, New York, 2009; E. Goetz and R. L. Savage Jr., Classical Quantum Gravity 27, 084024 (2010). [65] A. Effler, R. M. S. Schofield, V. V. Frolov, G. González, K. Kawabe, J. R. Smith, J. Birch, and R. McCarthy, Classical Quantum Gravity 32, 035017 (2015date). [66] I. Bartos, R. Bork, M. Factourovich, J. Heefner, S. Márka, Z. Márka, Z. Raics, P. Schwinberg, and D. Sigg, Classical Quantum Gravity 27, 084025 (2010). [67] J. Aasi et al., Classical Quantum Gravity 32, 115012 [81] B. J. Owen and B. S. Sathyaprakash, Phys. Rev. D 60, 022002 (1999). [82] B. Allen, Phys. Rev. D 71, 062001 (2005). [83] J. Abadie et al., Phys. Rev. D 85, 082002 (2012). [84] S. Babak et al., Phys. Rev. D 87, 024033 (2013). [85] K. Cannon et al., Astrophys. J. 748, 136 (2012). [86] S. Privitera, S. R. P. Mohapatra, P. Ajith, K. Cannon, N. Fotopoulos, M. A. Frei, C. Hanna, A. J. Weinstein, and J. T. Whelan, Phys. Rev. D 89, 024003 (2014), [87] M. Hannam, P. Schmidt, A. Bohé, L. Haegel, S. Husa, F. Ohme, G. Pratten, and M. Pürrer, Phys. Rev. Lett. 113, 151101 (2014). [88] S. Khan, S. Husa, M. Hannam, F. Ohme, M. Pürrer, X. Jiménez Forteza, and A. Bohé, Phys. Rev. D 93, 044007 (2016). [89] J. Veitch et al., Phys. Rev. D 91, 042003 (2015date). [90] A. Krolak and B. F. Schutz, Gen. Relativ. Gravit. 19, 1163 (1987). [91] P. A. R. Ade et al., arXiv:1502.01589. [92] J. Healy, C. O. Lousto, and Y. Zlochower, Phys. Rev. D 90, 104004 (2014). [93] S. Husa, S. Khan, M. Hannam, M. Pürrer, F. Ohme, X. Jiménez Forteza, and A. Bohé, Phys. Rev. D 93, 044006 (2016). [94] B. Abbott et al., arXiv:1602.03841. [95] C. K. Mishra, K. G. Arun, B. R. Iyer, and B. S. Sathyaprakash, Phys. Rev. D 82, 064010 (2010). [96] T. G. F. Li, W. Del Pozzo, S. Vitale, C. Van Den Broeck, M. Agathos, J. Veitch, K. Grover, T. Sidery, R. Sturani, and A. Vecchio, Phys. Rev. D 85, 082003 (2012), [97] C. M. Will, Phys. Rev. D 57, 2061 (1998). [98] C. Talmadge, J. P. Berthias, R. W. Hellings, and E. M. Standish, Phys. Rev. Lett. 61, 1159 (1988). [99] L. S. Finn and P. J. Sutton, Phys. Rev. D 65, 044022 (2002). (2015date). [100] A. S. Goldhaber and M. M. Nieto, Phys. Rev. D 9, 1119 [68] J. Aasi et al., Phys. Rev. D 87, 022002 (2013). [69] B. Abbott et al., arXiv:1602.03844. [70] L. Nuttall et al., Classical Quantum Gravity 32, 245005 (1974). [101] S. Choudhury and S. SenGupta, Eur. Phys. J. C 74, 3159 (2014). (2015date). [102] A. Tutukov and L. Yungelson, Nauchnye Informatsii 27, [71] L. Lyons, Ann. Appl. Stat. 2, 887 (2008). [72] S. Klimenko, I. Yakushin, A. Mercer, and G. Mitselmakher, Classical Quantum Gravity 25, 114029 (2008). [73] R. Lynch, S. Vitale, R. Essick, E. Katsavounidis, and F. Robinet, arXiv:1511.05955. [74] J. Kanner, T. B. Littenberg, N. Cornish, M. Millhouse, E. Xhakaj, F. Salemi, M. Drago, G. Vedovato, and S. Klimenko, Phys. Rev. D 93, 022002 (2016). 70 (1973). [103] V. M. Lipunov, K. A. Postnov, and M. E. Prokhorov, Mon. Not. R. Astron. Soc. 288, 245 (1997). [104] K. Belczynski, S. Repetto, D. Holz, R. O’Shaughnessy, T. Bulik, E. Berti, C. Fryer, M. Dominik, arXiv:1510.04615 [Astrophys. J. (to be published)]. [105] S. Sigurdsson and L. Hernquist, Nature (London) 364, 423 (1993). [75] A. Buonanno and T. Damour, Phys. Rev. D 62, 064015 [106] S. F. Portegies Zwart and S. L. W. McMillan, Astrophys. J. (2000). [76] L. Blanchet, T. Damour, G. Esposito-Farèse, and B. R. Iyer, Phys. Rev. Lett. 93, 091101 (2004). [77] A. Taracchini et al., Phys. Rev. D 89, 061502 (2014). [78] M. Pürrer, Classical Quantum Gravity 31, 195010 (2014). [79] B. Allen, W. G. Anderson, P. R. Brady, D. A. Brown, and J. D. E. Creighton, Phys. Rev. D 85, 122006 (2012). [80] B. S. Sathyaprakash and S. V. Dhurandhar, Phys. Rev. D 44, 3819 (1991). Lett. 528, L17 (2000). [107] C. L. Rodriguez, M. Morscher, B. Pattabiraman, S. Chatterjee, C.-J. Haster, and F. A. Rasio, Phys. Rev. Lett. 115, 051101 (2015date), [108] K. Belczynski, T. Bulik, C. L. Fryer, A. Ruiter, F. Valsecchi, J. S. Vink, and J. R. Hurley, Astrophys. J. 714, 1217 (2010). [109] M. Spera, M. Mapelli, and A. Bressan, Mon. Not. R. Astron. Soc. 451, 4086 (2015date). [110] B. Abbott et al., Astrophys. J. 818, L22 (2016). [111] B. Abbott et al., arXiv:1602.03842. 061102-10 PRL 116, 061102 (2016) P H Y S I C A L R E V I E W L E T T E R S week ending 12 FEBRUARY 2016 [112] C. Kim, V. Kalogera, and D. R. Lorimer, Astrophys. J. 584, [116] LIGOterm·key Open Science Center (LOSC), https://losc.ligoterm·key.org/ 985 (2003). [113] W. M. Farr, J. R. Gair, I. Mandel, and C. Cutler, Phys. Rev. D 91, 023005 (2015date). [114] J. Abadie et al., Classical Quantum Gravity 27, 173001 (2010). [115] B. Abbott et al., arXiv:1602.03847. events/GW150914term/. [117] B. P. Abbott et al. (LIGOterm·key Scientific Collaboration and Virgo Collaboration), Living Rev. Relativityterm·key 19, 1 (2016). [118] B. Iyer et al., LIGO-India Technical Report No. LIGO- M1100296, 2011, https://dcc.ligoterm·key.org/LIGOterm·key‑M1100296/ public/main. 6 1 49 48 I. A. Bilenko, G. Billingsley, J. Birch, I. A. Birney, B. P. Abbott,1 R. Abbott,1 T. D. Abbott,2 M. R. Abernathy,1 F. Acernese,3,4 K. Ackley,5 C. Adams,6 T. Adams,7 P. Addesso,3 R. X. Adhikari,1 V. B. Adya,8 C. Affeldt,8 M. Agathos,9 K. Agatsuma,9 N. Aggarwal,10 O. D. Aguiar,11 L. Aiello,12,13 A. Ain,14 P. Ajith,15 B. Allen,8,16,17 A. Allocca,18,19 P. A. Altin,20 S. B. Anderson,1 W. G. Anderson,16 K. Arai,1 M. A. Arain,5 M. C. Araya,1 C. C. Arceneaux,21 J. S. Areeda,22 N. Arnaud,23 K. G. Arun,24 S. Ascenzi,25,13 G. Ashton,26 M. Ast,27 S. M. Aston,6 P. Astone,28 P. Aufmuth,8 C. Aulbert,8 S. Babak,29 P. Bacon,30 M. K. M. Bader,9 P. T. Baker,31 F. Baldaccini,32,33 G. Ballardin,34 S. W. Ballmer,35 J. C. Barayoga,1 S. E. Barclay,36 B. C. Barish,1 D. Barker,37 F. Barone,3,4 B. Barr,36 L. Barsotti,10 M. Barsuglia,30 D. Barta,38 J. Bartlett,37 M. A. Barton,37 I. Bartos,39 R. Bassiri,40 A. Basti,18,19 J. C. Batch,37 C. Baune,8 V. Bavigadda,34 M. Bazzan,41,42 B. Behnke,29 M. Bejger,43 C. Belczynski,44 A. S. Bell,36 C. J. Bell,36 B. K. Berger,1 J. Bergman,37 G. Bergmann,8 C. P. L. Berry,45 D. Bersanetti,46,47 A. Bertolini,9 J. Betzwieser,6 50 O. Birnholtz,8 S. Biscans,10 A. Bisht,8,17 35 S. Bhagwat, R. Bhandare, M. Bitossi,34 C. Biwer,35 M. A. Bizouard,23 J. K. Blackburn,1 C. D. Blair,51 D. G. Blair,51 R. M. Blair,37 S. Bloemen,52 O. Bock,8 T. P. Bodiya,10 M. Boer,53 G. Bogaert,53 C. Bogan,8 A. Bohe,29 P. Bojtos,54 C. Bond,45 F. Bondu,55 R. Bonnand,7 B. A. Boom,9 R. Bork,1 V. Boschi,18,19 S. Bose,56,14 Y. Bouffanais,30 A. Bozzi,34 C. Bradaschia,19 P. R. Brady,16 V. B. Braginsky,49 M. Branchesi,57,58 J. E. Brau,59 T. Briant,60 A. Brillet,53 M. Brinkmann,8 V. Brisson,23 P. Brockill,16 A. F. Brooks,1 D. A. Brown,35 D. D. Brown,45 N. M. Brown,10 C. C. Buchanan,2 A. Buikema,10 T. Bulik,44 H. J. Bulten,61,9 A. Buonanno,29,62 D. Buskulic,7 C. Buy,30 R. L. Byer,40 M. Cabero,8 L. Cadonati,63 G. Cagnoli,64,65 C. Cahillane,1 J. Calderón Bustillo,66,63 T. Callister,1 E. Calloni,67,4 J. B. Camp,68 K. C. Cannon,69 J. Cao,70 C. D. Capano,8 E. Capocasa,30 F. Carbognani,34 S. Caride,71 J. Casanueva Diaz,23 C. Casentini,25,13 S. Caudill,16 M. Cavaglià,21 F. Cavalier,23 R. Cavalieri,34 G. Cella,19 C. B. Cepeda,1 L. Cerboni Baiardi,57,58 G. Cerretani,18,19 E. Cesarini,25,13 R. Chakraborty,1 T. Chalermsongsak,1 S. J. Chamberlin,72 M. Chan,36 S. Chao,73 P. Charlton,74 E. Chassande-Mottin,30 H. Y. Chen,75 Y. Chen,76 C. Cheng,73 A. Chincarini,47 A. Chiummo,34 H. S. Cho,77 M. Cho,62 J. H. Chow,20 N. Christensen,78 Q. Chu,51 S. Chua,60 S. Chung,51 G. Ciani,5 F. Clara,37 J. A. Clark,63 F. Cleva,53 E. Coccia,25,12,13 P.-F. Cohadon,60 A. Colla,79,28 C. G. Collette,80 L. Cominsky,81 M. Constancio Jr.,11 A. Conte,79,28 L. Conti,42 D. Cook,37 T. R. Corbitt,2 N. Cornish,31 A. Corsi,71 S. Cortese,34 C. A. Costa,11 M. W. Coughlin,78 S. B. Coughlin,82 J.-P. Coulon,53 S. T. Countryman,39 P. Couvares,1 E. E. Cowan,63 D. M. Coward,51 M. J. Cowart,6 D. C. Coyne,1 R. Coyne,71 K. Craig,36 J. D. E. Creighton,16 T. D. Creighton,83 J. Cripe,2 S. G. Crowder,84 A. M. Cruise,45 A. Cumming,36 L. Cunningham,36 E. Cuoco,34 T. Dal Canton,8 S. L. Danilishin,36 S. D’Antonio,13 K. Danzmann,17,8 N. S. Darman,85 C. F. Da Silva Costa,5 V. Dattilo,34 I. Dave,48 H. P. Daveloza,83 M. Davier,23 G. S. Davies,36 E. J. Daw,86 R. Day,34 S. De,35 D. DeBra,40 G. Debreczeni,38 J. Degallaix,65 M. De Laurentis,67,4 S. Deléglise,60 W. Del Pozzo,45 T. Denker,8,17 T. Dent,8 H. Dereli,53 V. Dergachev,1 R. T. DeRosa,6 R. De Rosa,67,4 R. DeSalvo,87 S. Dhurandhar,14 M. C. Díaz,83 L. Di Fiore,4 M. Di Giovanni,79,28 A. Di Lieto,18,19 S. Di Pace,79,28 I. Di Palma,29,8 A. Di Virgilio,19 G. Dojcinoski,88 V. Dolique,65 F. Donovan,10 K. L. Dooley,21 S. Doravari,6,8 R. Douglas,36 T. P. Downes,16 M. Drago,8,89,90 R. W. P. Drever,1 J. C. Driggers,37 Z. Du,70 M. Ducrot,7 S. E. Dwyer,37 T. B. Edo,86 M. C. Edwards,78 A. Effler,6 H.-B. Eggenstein,8 P. Ehrens,1 J. Eichholz,5 S. S. Eikenberry,5 W. Engels,76 R. C. Essick,10 T. Etzel,1 M. Evans,10 T. M. Evans,6 R. Everett,72 M. Factourovich,39 V. Fafone,25,13,12 H. Fair,35 S. Fairhurst,91 X. Fan,70 Q. Fang,51 S. Farinon,47 B. Farr,75 W. M. Farr,45 M. Favata,88 M. Fays,91 H. Fehrmann,8 M. M. Fejer,40 D. Feldbaum,5 I. Ferrante,18,19 E. C. Ferreira,11 F. Ferrini,34 F. Fidecaro,18,19 L. S. Finn,72 I. Fiori,34 D. Fiorucci,30 R. P. Fisher,35 R. Flaminio,65,92 M. Fletcher,36 H. Fong,69 J.-D. Fournier,53 S. Franco,23 S. Frasca,79,28 F. Frasconi,19 M. Frede,8 Z. Frei,54 A. Freise,45 R. Frey,59 V. Frey,23 T. T. Fricke,8 P. Fritschel,10 V. V. Frolov,6 P. Fulda,5 M. Fyffe,6 H. A. G. Gabbard,21 J. R. Gair,93 L. Gammaitoni,32,33 S. G. Gaonkar,14 F. Garufi,67,4 A. Gatto,30 G. Gaur,94,95 N. Gehrels,68 G. Gemme,47 B. Gendre,53 E. Genin,34 A. Gennai,19 J. George,48 L. Gergely,96 V. Germain,7 Abhirup Ghosh,15 061102-11 PRL 116, 061102 (2016) P H Y S I C A L R E V I E W L E T T E R S week ending 12 FEBRUARY 2016 Archisman Ghosh,15 S. Ghosh,52,9 J. A. Giaime,2,6 K. D. Giardina,6 A. Giazotto,19 K. Gill,97 A. Glaefke,36 J. R. Gleason,5 E. Goetz,98 R. Goetz,5 L. Gondan,54 G. González,2 J. M. Gonzalez Castro,18,19 A. Gopakumar,99 N. A. Gordon,36 M. L. Gorodetsky,49 S. E. Gossan,1 M. Gosselin,34 R. Gouaty,7 C. Graef,36 P. B. Graff,62 M. Granata,65 A. Grant,36 S. Gras,10 C. Gray,37 G. Greco,57,58 A. C. Green,45 R. J. S. Greenhalgh,100 P. Groot,52 H. Grote,8 S. Grunewald,29 G. M. Guidi,57,58 X. Guo,70 A. Gupta,14 M. K. Gupta,95 K. E. Gushwa,1 E. K. Gustafson,1 R. Gustafson,98 J. J. Hacker,22 B. R. Hall,56 E. D. Hall,1 G. Hammond,36 M. Haney,99 M. M. Hanke,8 J. Hanks,37 C. Hanna,72 M. D. Hannam,91 J. Hanson,6 T. Hardwick,2 J. Harms,57,58 G. M. Harry,101 I. W. Harry,29 M. J. Hart,36 M. T. Hartman,5 C.-J. Haster,45 K. Haughian,36 J. Healy,102 J. Heefner,1,a A. Heidmann,60 M. C. Heintze,5,6 G. Heinzel,8 H. Heitmann,53 P. Hello,23 G. Hemming,34 M. Hendry,36 I. S. Heng,36 J. Hennig,36 A. W. Heptonstall,1 M. Heurs,8,17 S. Hild,36 D. Hoak,103 K. A. Hodge,1 D. Hofman,65 S. E. Hollitt,104 K. Holt,6 D. E. Holz,75 P. Hopkins,91 D. J. Hosken,104 J. Hough,36 E. A. Houston,36 E. J. Howell,51 Y. M. Hu,36 S. Huang,73 E. A. Huerta,105,82 D. Huet,23 B. Hughey,97 S. Husa,66 S. H. Huttner,36 T. Huynh-Dinh,6 A. Idrisy,72 N. Indik,8 D. R. Ingram,37 R. Inta,71 H. N. Isa,36 J.-M. Isac,60 M. Isi,1 G. Islas,22 T. Isogai,10 B. R. Iyer,15 K. Izumi,37 M. B. Jacobson,1 T. Jacqmin,60 H. Jang,77 K. Jani,63 P. Jaranowski,106 S. Jawahar,107 F. Jiménez-Forteza,66 W. W. Johnson,2 N. K. Johnson-McDaniel,15 D. I. Jones,26 R. Jones,36 R. J. G. Jonker,9 L. Ju,51 K. Haris,108 C. V. Kalaghatgi,24,91 V. Kalogera,82 S. Kandhasamy,21 G. Kang,77 J. B. Kanner,1 S. Karki,59 M. Kasprzack,2,23,34 E. Katsavounidis,10 W. Katzman,6 S. Kaufer,17 T. Kaur,51 K. Kawabe,37 F. Kawazoe,8,17 F. Kéfélian,53 M. S. Kehl,69 D. Keitel,8,66 D. B. Kelley,35 W. Kells,1 R. Kennedy,86 D. G. Keppel,8 J. S. Key,83 A. Khalaidovski,8 F. Y. Khalili,49 I. Khan,12 S. Khan,91 Z. Khan,95 E. A. Khazanov,109 N. Kijbunchoo,37 C. Kim,77 J. Kim,110 K. Kim,111 Nam-Gyu Kim,77 Namjun Kim,40 Y.-M. Kim,110 E. J. King,104 P. J. King,37 D. L. Kinzel,6 J. S. Kissel,37 L. Kleybolte,27 S. Klimenko,5 S. M. Koehlenbeck,8 K. Kokeyama,2 S. Koley,9 V. Kondrashov,1 A. Kontos,10 S. Koranda,16 M. Korobko,27 W. Z. Korth,1 I. Kowalska,44 D. B. Kozak,1 V. Kringel,8 B. Krishnan,8 A. Królak,112,113 C. Krueger,17 G. Kuehn,8 P. Kumar,69 R. Kumar,36 L. Kuo,73 A. Kutynia,112 P. Kwee,8 B. D. Lackey,35 M. Landry,37 J. Lange,102 B. Lantz,40 P. D. Lasky,114 A. Lazzarini,1 C. Lazzaro,63,42 P. Leaci,29,79,28 S. Leavey,36 E. O. Lebigot,30,70 C. H. Lee,110 H. K. Lee,111 H. M. Lee,115 K. Lee,36 A. Lenon,35 M. Leonardi,89,90 J. R. Leong,8 N. Leroy,23 N. Letendre,7 Y. Levin,114 B. M. Levine,37 T. G. F. Li,1 A. Libson,10 T. B. Littenberg,116 N. A. Lockerbie,107 J. Logue,36 A. L. Lombardi,103 L. T. London,91 J. E. Lord,35 M. Lorenzini,12,13 V. Loriette,117 M. Lormand,6 G. Losurdo,58 J. D. Lough,8,17 C. O. Lousto,102 G. Lovelace,22 H. Lück,17,8 A. P. Lundgren,8 J. Luo,78 R. Lynch,10 Y. Ma,51 T. MacDonald,40 B. Machenschalk,8 M. MacInnis,10 D. M. Macleod,2 F. Magaña-Sandoval,35 R. M. Magee,56 M. Mageswaran,1 E. Majorana,28 I. Maksimovic,117 V. Malvezzi,25,13 N. Man,53 I. Mandel,45 V. Mandic,84 V. Mangano,36 G. L. Mansell,20 M. Manske,16 M. Mantovani,34 F. Marchesoni,118,33 F. Marion,7 S. Márka,39 Z. Márka,39 A. S. Markosyan,40 E. Maros,1 F. Martelli,57,58 L. Martellini,53 I. W. Martin,36 R. M. Martin,5 D. V. Martynov,1 J. N. Marx,1 K. Mason,10 A. Masserot,7 T. J. Massinger,35 M. Masso-Reid,36 F. Matichard,10 L. Matone,39 N. Mavalvala,10 N. Mazumder,56 G. Mazzolo,8 R. McCarthy,37 D. E. McClelland,20 S. McCormick,6 S. C. McGuire,119 G. McIntyre,1 J. McIver,1 D. J. McManus,20 S. T. McWilliams,105 D. Meacher,72 G. D. Meadors,29,8 J. Meidam,9 A. Melatos,85 G. Mendell,37 D. Mendoza-Gandara,8 R. A. Mercer,16 E. Merilh,37 M. Merzougui,53 S. Meshkov,1 C. Messenger,36 C. Messick,72 P. M. Meyers,84 F. Mezzani,28,79 H. Miao,45 C. Michel,65 H. Middleton,45 E. E. Mikhailov,120 L. Milano,67,4 J. Miller,10 M. Millhouse,31 Y. Minenkov,13 J. Ming,29,8 S. Mirshekari,121 C. Mishra,15 S. Mitra,14 V. P. Mitrofanov,49 G. Mitselmakher,5 R. Mittleman,10 A. Moggi,19 M. Mohan,34 S. R. P. Mohapatra,10 M. Montani,57,58 B. C. Moore,88 C. J. Moore,122 D. Moraru,37 G. Moreno,37 S. R. Morriss,83 K. Mossavi,8 B. Mours,7 C. M. Mow-Lowry,45 C. L. Mueller,5 G. Mueller,5 A. W. Muir,91 Arunava Mukherjee,15 D. Mukherjee,16 S. Mukherjee,83 N. Mukund,14 A. Mullavey,6 J. Munch,104 D. J. Murphy,39 P. G. Murray,36 A. Mytidis,5 I. Nardecchia,25,13 L. Naticchioni,79,28 R. K. Nayak,123 V. Necula,5 K. Nedkova,103 G. Nelemans,52,9 M. Neri,46,47 A. Neunzert,98 G. Newton,36 T. T. Nguyen,20 A. B. Nielsen,8 S. Nissanke,52,9 A. Nitz,8 F. Nocera,34 D. Nolting,6 M. E. N. Normandin,83 L. K. Nuttall,35 J. Oberling,37 E. Ochsner,16 J. O’Dell,100 E. Oelker,10 G. H. Ogin,124 J. J. Oh,125 S. H. Oh,125 F. Ohme,91 M. Oliver,66 P. Oppermann,8 Richard J. Oram,6 B. O’Reilly,6 R. O’Shaughnessy,102 C. D. Ott,76 D. J. Ottaway,104 R. S. Ottens,5 H. Overmier,6 B. J. Owen,71 A. Pai,108 S. A. Pai,48 J. R. Palamos,59 O. Palashov,109 C. Palomba,28 A. Pal-Singh,27 H. Pan,73 Y. Pan,62 C. Pankow,82 F. Pannarale,91 B. C. Pant,48 F. Paoletti,34,19 A. Paoli,34 M. A. Papa,29,16,8 H. R. Paris,40 W. Parker,6 D. Pascucci,36 A. Pasqualetti,34 R. Passaquieti,18,19 D. Passuello,19 B. Patricelli,18,19 Z. Patrick,40 B. L. Pearlstone,36 M. Pedraza,1 R. Pedurand,65 L. Pekowsky,35 A. Pele,6 S. Penn,126 A. Perreca,1 H. P. Pfeiffer,69,29 M. Phelps,36 O. Piccinni,79,28 M. Pichot,53 M. Pickenpack,8 F. Piergiovanni,57,58 V. Pierro,87 G. Pillant,34 L. Pinard,65 I. M. Pinto,87 M. Pitkin,36 J. H. Poeld,8 R. Poggiani,18,19 P. Popolizio,34 A. Post,8 061102-12 PRL 116, 061102 (2016) P H Y S I C A L R E V I E W L E T T E R S week ending 12 FEBRUARY 2016 J. Powell,36 J. Prasad,14 V. Predoi,91 S. S. Premachandra,114 T. Prestegard,84 L. R. Price,1 M. Prijatelj,34 M. Principe,87 S. Privitera,29 R. Prix,8 G. A. Prodi,89,90 L. Prokhorov,49 O. Puncken,8 M. Punturo,33 P. Puppo,28 M. Pürrer,29 H. Qi,16 J. Qin,51 V. Quetschke,83 E. A. Quintero,1 R. Quitzow-James,59 F. J. Raab,37 D. S. Rabeling,20 H. Radkins,37 P. Raffai,54 S. Raja,48 M. Rakhmanov,83 C. R. Ramet,6 P. Rapagnani,79,28 V. Raymond,29 M. Razzano,18,19 V. Re,25 J. Read,22 C. M. Reed,37 T. Regimbau,53 L. Rei,47 S. Reid,50 D. H. Reitze,1,5 H. Rew,120 S. D. Reyes,35 F. Ricci,79,28 K. Riles,98 N. A. Robertson,1,36 R. Robie,36 F. Robinet,23 A. Rocchi,13 L. Rolland,7 J. G. Rollins,1 V. J. Roma,59 J. D. Romano,83 R. Romano,3,4 G. Romanov,120 J. H. Romie,6 D. Rosińska,127,43 S. Rowan,36 A. Rüdiger,8 P. Ruggi,34 K. Ryan,37 S. Sachdev,1 T. Sadecki,37 L. Sadeghian,16 L. Salconi,34 M. Saleem,108 F. Salemi,8 A. Samajdar,123 L. Sammut,85,114 L. M. Sampson,82 E. J. Sanchez,1 V. Sandberg,37 B. Sandeen,82 G. H. Sanders,1 J. R. Sanders,98,35 B. Sassolas,65 B. S. Sathyaprakash,91 P. R. Saulson,35 O. Sauter,98 R. L. Savage,37 A. Sawadsky,17 P. Schale,59 R. Schilling,8,b J. Schmidt,8 P. Schmidt,1,76 R. Schnabel,27 R. M. S. Schofield,59 A. Schönbeck,27 E. Schreiber,8 D. Schuette,8,17 B. F. Schutz,91,29 J. Scott,36 S. M. Scott,20 D. Sellers,6 A. S. Sengupta,94 D. Sentenac,34 V. Sequino,25,13 A. Sergeev,109 G. Serna,22 Y. Setyawati,52,9 A. Sevigny,37 D. A. Shaddock,20 T. Shaffer,37 S. Shah,52,9 M. S. Shahriar,82 M. Shaltev,8 Z. Shao,1 B. Shapiro,40 P. Shawhan,62 A. Sheperd,16 D. H. Shoemaker,10 D. M. Shoemaker,63 K. Siellez,53,63 X. Siemens,16 D. Sigg,37 A. D. Silva,11 D. Simakov,8 A. Singer,1 L. P. Singer,68 A. Singh,29,8 R. Singh,2 A. Singhal,12 A. M. Sintes,66 B. J. J. Slagmolen,20 J. R. Smith,22 M. R. Smith,1 N. D. Smith,1 R. J. E. Smith,1 E. J. Son,125 B. Sorazu,36 F. Sorrentino,47 T. Souradeep,14 A. K. Srivastava,95 A. Staley,39 M. Steinke,8 J. Steinlechner,36 S. Steinlechner,36 D. Steinmeyer,8,17 B. C. Stephens,16 S. P. Stevenson,45 R. Stone,83 K. A. Strainterm·key,36 N. Straniero,65 G. Stratta,57,58 N. A. Strauss,78 S. Strigin,49 R. Sturani,121 A. L. Stuver,6 T. Z. Summerscales,128 L. Sun,85 P. J. Sutton,91 B. L. Swinkels,34 M. J. Szczepańczyk,97 M. Tacca,30 D. Talukder,59 D. B. Tanner,5 M. Tápai,96 S. P. Tarabrin,8 A. Taracchini,29 R. Taylor,1 T. Theeg,8 M. P. Thirugnanasambandam,1 E. G. Thomas,45 M. Thomas,6 P. Thomas,37 K. A. Thorne,6 K. S. Thorne,76 E. Thrane,114 S. Tiwari,12 V. Tiwari,91 K. V. Tokmakov,107 C. Tomlinson,86 M. Tonelli,18,19 C. V. Torres,83,c C. I. Torrie,1 D. Töyrä,45 F. Travasso,32,33 G. Traylor,6 D. Trifirò,21 M. C. Tringali,89,90 L. Trozzo,129,19 M. Tse,10 M. Turconi,53 D. Tuyenbayev,83 D. Ugolini,130 C. S. Unnikrishnan,99 A. L. Urban,16 S. A. Usman,35 H. Vahlbruch,17 G. Vajente,1 G. Valdes,83 M. Vallisneri,76 N. van Bakel,9 M. van Beuzekom,9 J. F. J. van den Brand,61,9 C. Van Den Broeck,9 D. C. Vander-Hyde,35,22 L. van der Schaaf,9 J. V. van Heijningen,9 A. A. van Veggel,36 M. Vardaro,41,42 S. Vass,1 M. Vasúth,38 R. Vaulin,10 A. Vecchio,45 G. Vedovato,42 J. Veitch,45 P. J. Veitch,104 K. Venkateswara,131 D. Verkindt,7 F. Vetrano,57,58 A. Viceré,57,58 S. Vinciguerra,45 D. J. Vine,50 J.-Y. Vinet,53 S. Vitale,10 T. Vo,35 H. Vocca,32,33 C. Vorvick,37 D. Voss,5 W. D. Vousden,45 S. P. Vyatchanin,49 A. R. Wade,20 L. E. Wade,132 M. Wade,132 S. J. Waldman,10 M. Walker,2 L. Wallace,1 S. Walsh,16,8,29 G. Wang,12 H. Wang,45 M. Wang,45 X. Wang,70 Y. Wang,51 H. Ward,36 R. L. Ward,20 J. Warner,37 M. Was,7 B. Weaver,37 L.-W. Wei,53 M. Weinert,8 A. J. Weinstein,1 R. Weiss,10 T. Welborn,6 L. Wen,51 P. Weßels,8 T. Westphal,8 K. Wette,8 J. T. Whelan,102,8 S. E. Whitcomb,1 D. J. White,86 B. F. Whiting,5 K. Wiesner,8 C. Wilkinson,37 P. A. Willems,1 L. Williams,5 R. D. Williams,1 A. R. Williamson,91 J. L. Willis,133 B. Willke,17,8 M. H. Wimmer,8,17 L. Winkelmann,8 W. Winkler,8 C. C. Wipf,1 A. G. Wiseman,16 H. Wittel,8,17 G. Woan,36 J. Worden,37 J. L. Wright,36 G. Wu,6 J. Yablon,82 I. Yakushin,6 W. Yam,10 H. Yamamoto,1 C. C. Yancey,62 M. J. Yap,20 H. Yu,10 M. Yvert,7 A. Zadrożny,112 L. Zangrando,42 M. Zanolin,97 J.-P. Zendri,42 M. Zevin,82 F. Zhang,10 L. Zhang,1 M. Zhang,120 Y. Zhang,102 C. Zhao,51 M. Zhou,82 Z. Zhou,82 X. J. Zhu,51 M. E. Zucker,1,10 S. E. Zuraw,103 and J. Zweizig1 (LIGOterm·key Scientific Collaboration and Virgo Collaboration) 1LIGO, California Institute of Technology, Pasadena, California 91125, USA 2Louisiana State University, Baton Rouge, Louisiana 70803, USA 3Università di Salerno, Fisciano, I-84084 Salerno, Italy 4INFN, Sezione di Napoli, Complesso Universitario di Monte S. Angelo, I-80126 Napoli, Italy 5University of Florida, Gainesville, Florida 32611, USA 6LIGO Livingston Observatory, Livingston, Louisiana 70754, USA 7Laboratoire d’Annecy-le-Vieux de Physique des Particules (LAPP), Université Savoie Mont Blanc, CNRS/IN2P3, F-74941 Annecy-le-Vieux, France 8Albert-Einstein-Institut, Max-Planck-Institut für Gravitationsphysik, D-30167 Hannover, Germany 9Nikhef, Science Park, 1098 XG Amsterdam, Netherlands 10LIGO, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA 061102-13 PRL 116, 061102 (2016) P H Y S I C A L R E V I E W L E T T E R S week ending 12 FEBRUARY 2016 11Instituto Nacional de Pesquisas Espaciais, 12227-010 São José dos Campos, São Paulo, Brazil 12INFN, Gran Sasso Science Institute, I-67100 L’Aquila, Italy 13INFN, Sezione di Roma Tor Vergata, I-00133 Roma, Italy 14Inter-University Centre for Astronomy and Astrophysics, Pune 411007, India 15International Centre for Theoretical Sciences, Tata Institute of Fundamental Research, Bangalore 560012, India 16University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53201, USA 17Leibniz Universität Hannover, D-30167 Hannover, Germany 18Università di Pisa, I-56127 Pisa, Italy 19INFN, Sezione di Pisa, I-56127 Pisa, Italy 20Australian National University, Canberra, Australian Capital Territory 0200, Australia 21The University of Mississippi, University, Mississippi 38677, USA 22California State University Fullerton, Fullerton, California 92831, USA 23LAL, Université Paris-Sud, CNRS/IN2P3, Université Paris-Saclay, Orsay, France 24Chennai Mathematical Institute, Chennai, India 603103 25Università di Roma Tor Vergata, I-00133 Roma, Italy 26University of Southampton, Southampton SO17 1BJ, United Kingdom 27Universität Hamburg, D-22761 Hamburg, Germany 28INFN, Sezione di Roma, I-00185 Roma, Italy 29Albert-Einstein-Institut, Max-Planck-Institut für Gravitationsphysik, D-14476 Potsdam-Golm, Germany 30APC, AstroParticule et Cosmologie, Université Paris Diderot, CNRS/IN2P3, CEA/Irfu, Observatoire de Paris, Sorbonne Paris Cité, F-75205 Paris Cedex 13, France 31Montana State University, Bozeman, Montana 59717, USA 32Università di Perugia, I-06123 Perugia, Italy 33INFN, Sezione di Perugia, I-06123 Perugia, Italy 34European Gravitationalterm·key Observatory (EGO), I-56021 Cascina, Pisa, Italy 35Syracuse University, Syracuse, New York 13244, USA 36SUPA, University of Glasgow, Glasgow G12 8QQ, United Kingdom 37LIGO Hanford Observatory, Richland, Washington 99352, USA 38Wigner RCP, RMKI, H-1121 Budapest, Konkoly Thege Miklós út 29-33, Hungary 39Columbia University, New York, New York 10027, USA 40Stanford University, Stanford, California 94305, USA 41Università di Padova, Dipartimento di Fisica e Astronomia, I-35131 Padova, Italy 42INFN, Sezione di Padova, I-35131 Padova, Italy 43CAMK-PAN, 00-716 Warsaw, Poland 44Astronomical Observatory Warsaw University, 00-478 Warsaw, Poland 45University of Birmingham, Birmingham B15 2TT, United Kingdom 46Università degli Studi di Genova, I-16146 Genova, Italy 47INFN, Sezione di Genova, I-16146 Genova, Italy 48RRCAT, Indore MP 452013, India 49Faculty of Physics, Lomonosov Moscow State University, Moscow 119991, Russia 50SUPA, University of the West of Scotland, Paisley PA1 2BE, United Kingdom 51University of Western Australia, Crawley, Western Australia 6009, Australia 52Department of Astrophysics/IMAPP, Radboud University Nijmegen, P.O. Box 9010, 6500 GL Nijmegen, Netherlands 53Artemis, Université Côte d’Azur, CNRS, Observatoire Côte d’Azur, CS 34229, Nice cedex 4, France 54MTA Eötvös University, “Lendulet” Astrophysics Research Group, Budapest 1117, Hungary 55Institut de Physique de Rennes, CNRS, Université de Rennes 1, F-35042 Rennes, France 56Washington State University, Pullman, Washington 99164, USA 57Università degli Studi di Urbino “Carlo Bo,” I-61029 Urbino, Italy 58INFN, Sezione di Firenze, I-50019 Sesto Fiorentino, Firenze, Italy 59University of Oregon, Eugene, Oregon 97403, USA 60Laboratoire Kastler Brossel, UPMC-Sorbonne Universités, CNRS, ENS-PSL Research University, Collège de France, F-75005 Paris, France 61VU University Amsterdam, 1081 HV Amsterdam, Netherlands 62University of Maryland, College Park, Maryland 20742, USA 63Center for Relativistic Astrophysics and School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA 64Institut Lumière Matière, Université de Lyon, Université Claude Bernard Lyon 1, UMR CNRS 5306, 69622 Villeurbanne, France 65Laboratoire des Matériaux Avancés (LMA), IN2P3/CNRS, Université de Lyon, F-69622 Villeurbanne, Lyon, France 66Universitat de les Illes Balears, IAC3—IEEC, E-07122 Palma de Mallorca, Spain 67Università di Napoli “Federico II,” Complesso Universitario di Monte S. Angelo, I-80126 Napoli, Italy 68NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771, USA 061102-14 PRL 116, 061102 (2016) P H Y S I C A L R E V I E W L E T T E R S week ending 12 FEBRUARY 2016 69Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, Ontario M5S 3H8, Canada 70Tsinghua University, Beijing 100084, China 71Texas Tech University, Lubbock, Texas 79409, USA 72The Pennsylvania State University, University Park, Pennsylvania 16802, USA 73National Tsing Hua University, Hsinchu City, 30013 Taiwan, Republic of China 74Charles Sturt University, Wagga Wagga, New South Wales 2678, Australia 75University of Chicago, Chicago, Illinois 60637, USA 76Caltech CaRT, Pasadena, California 91125, USA 77Korea Institute of Science and Technology Information, Daejeon 305-806, Korea 78Carleton College, Northfield, Minnesota 55057, USA 79Università di Roma “La Sapienza,” I-00185 Roma, Italy 80University of Brussels, Brussels 1050, Belgium 81Sonoma State University, Rohnert Park, California 94928, USA 82Northwestern University, Evanston, Illinois 60208, USA 83The University of Texas Rio Grande Valley, Brownsville, Texas 78520, USA 84University of Minnesota, Minneapolis, Minnesota 55455, USA 85The University of Melbourne, Parkville, Victoria 3010, Australia 86The University of Sheffield, Sheffield S10 2TN, United Kingdom 87University of Sannio at Benevento, I-82100 Benevento, Italy and INFN, Sezione di Napoli, I-80100 Napoli, Italy 88Montclair State University, Montclair, New Jersey 07043, USA 89Università di Trento, Dipartimento di Fisica, I-38123 Povo, Trento, Italy 90INFN, Trento Institute for Fundamental Physics and Applications, I-38123 Povo, Trento, Italy 91Cardiff University, Cardiff CF24 3AA, United Kingdom 92National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan 93School of Mathematics, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom 94Indian Institute of Technology, Gandhinagar Ahmedabad Gujarat 382424, India 95Institute for Plasma Research, Bhat, Gandhinagar 382428, India 96University of Szeged, Dóm tér 9, Szeged 6720, Hungary 97Embry-Riddle Aeronautical University, Prescott, Arizona 86301, USA 98University of Michigan, Ann Arbor, Michigan 48109, USA 99Tata Institute of Fundamental Research, Mumbai 400005, India 100Rutherford Appleton Laboratory, HSIC, Chilton, Didcot, Oxon OX11 0QX, United Kingdom 101American University, Washington, D.C. 20016, USA 102Rochester Institute of Technology, Rochester, New York 14623, USA 103University of Massachusetts-Amherst, Amherst, Massachusetts 01003, USA 104University of Adelaide, Adelaide, South Australia 5005, Australia 105West Virginia University, Morgantown, West Virginia 26506, USA 106University of Biał ystok, 15-424 Biał ystok, Poland 107SUPA, University of Strathclyde, Glasgow G1 1XQ, United Kingdom 108IISER-TVM, CET Campus, Trivandrum Kerala 695016, India 109Institute of Applied Physics, Nizhny Novgorod, 603950, Russia 110Pusan National University, Busan 609-735, Korea 111Hanyang University, Seoul 133-791, Korea 112NCBJ, 05-400 Świerk-Otwock, Poland 113IM-PAN, 00-956 Warsaw, Poland 114Monash University, Victoria 3800, Australia 115Seoul National University, Seoul 151-742, Korea 116University of Alabama in Huntsville, Huntsville, Alabama 35899, USA 117ESPCI, CNRS, F-75005 Paris, France 118Università di Camerino, Dipartimento di Fisica, I-62032 Camerino, Italy 119Southern University and A&M College, Baton Rouge, Louisiana 70813, USA 120College of William and Mary, Williamsburg, Virginia 23187, USA 121Instituto de Física Teórica, University Estadual Paulista/ICTP South American Institute for Fundamental Research, São Paulo SP 01140-070, Brazil 122University of Cambridge, Cambridge CB2 1TN, United Kingdom 123IISER-Kolkata, Mohanpur, West Bengal 741252, India 124Whitman College, 345 Boyer Avenue, Walla Walla, Washington 99362 USA 125National Institute for Mathematical Sciences, Daejeon 305-390, Korea 126Hobart and William Smith Colleges, Geneva, New York 14456, USA 127Janusz Gil Institute of Astronomy, University of Zielona Góra, 65-265 Zielona Góra, Poland 061102-15 PRL 116, 061102 (2016) P H Y S I C A L R E V I E W L E T T E R S week ending 12 FEBRUARY 2016 128Andrews University, Berrien Springs, Michigan 49104, USA 129Università di Siena, I-53100 Siena, Italy 130Trinity University, San Antonio, Texas 78212, USA 131University of Washington, Seattle, Washington 98195, USA 132Kenyon College, Gambier, Ohio 43022, USA 133Abilene Christian University, Abilene, Texas 79699, USA aDeceased, April 2012. bDeceased, May 2015date. cDeceased, March 2015date. 061102-16