SWIFT Follow-up Observations of Candidate Gravitational-Wave Transient Events

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 eventswere selected with low latency by the network of GW detectors and their candidate sky locationswere observed by the Swift observatory. Image transient detection was used to analyze the collectedelectromagnetic data, which were found to be consistent with background. Off-line analysis of theGW data alone has also established that the selected GW events show no evidence of an astrophysicalorigin; one of them is consistent with background and the other one was a test, part of a “blind injectionchallenge”. With this work we demonstrate the feasibility of rapid follow-ups of GW transients andestablish the sensitivity improvement joint electromagnetic and GW observations could bring. This isa first step toward an electromagnetic follow-up program in the regime of routine detections with theadvanced GW instruments expected within this decade. In that regime multi-wavelength observationswill play a significant role in completing the astrophysical identification of GW sources. We presentthe methods and results from this first combined analysis and discuss its implications in terms ofsensitivity for the present and future instruments.