No Arabic 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.
This Supplement provides supporting material for arXiv:1602.08492 . We briefly summarize past electromagnetic (EM) follow-up efforts as well as the organization and policy of the current EM follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the EM follow-up observations that were performed in the different bands.
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 and their candidate sky locations were observed by the Swift observatory. 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.
The Advanced LIGO observatory recently reported the first direct detection of gravitational waves (GW) which triggered ALIGO on 2015 September 14. We report on observations taken with the Swift satellite two days after the trigger. No new X-ray, optical, UV or hard X-ray sources were detected in our observations, which were focussed on nearby galaxies in the GW error region and covered 4.7 square degrees (~2% of the probability in the rapidly-available GW error region; 0.3% of the probability from the final GW error region, which was produced several months after the trigger). We describe the rapid Swift response and automated analysis of the X-ray telescope and UV/Optical Telescope data, and note the importance to electromagnetic follow up of early notification of the progenitor details inferred from GW analysis.
The era of gravitational-wave astronomy began on 14 September 2015, when the LIGO Scientific Collaboration detected the merger of two $sim 30 M_odot$ black holes at a distance of $sim 400$ Mpc. This event has facilitated qualitatively new tests of gravitational theories, and has also produced exciting information about the astrophysical origin of black hole binaries. In this review we discuss the implications of this event for gravitational physics and astrophysics, as well as the expectations for future detections. In brief: (1) because the spins of the black holes could not be measured accurately and because mergers are not well calculated for modified theories of gravity, the current analysis of GW150914 does not place strong constraints on gravity variants that change only the generation of gravitational waves, but (2) it does strongly constrain alterations of the propagation of gravitational waves and alternatives to black holes. Finally, (3) many astrophysical models for the origin of heavy black hole binaries such as the GW150914 system are in play, but a reasonably robust conclusion that was reached even prior to the detection is that the environment of such systems needs to have a relatively low abundance of elements heavier than helium.
The Advanced LIGO observatory recently reported the first direct detection of gravitational waves predicted by Einstein (1916). We report on the first optical observations of the Gravitational Wave (GW) source GW150914 error region with the Global MASTER Robotic Net. We detected several optical transients, which proved to be unconnected with the GW event. Our result is consistent with the assumption that gravitational waves were produced by a binary black hole merger. The detection of the event confirmed the main prediction of the population synthesis performed with the Scenario Machine formulated in Lipunov1997b.