Fermi GBM Observations of LIGO Gravitational Wave event GW150914

V. Connaughton, C. M. Hui, P. Jenke, T. Littenberg, J. E. McEnery, J. Racusin, P. Shawhan, L. Singer, J. Veitch, C. A. Wilson-Hodge, P. N. Bhat, E. Bissaldi, W. Cleveland, M. H. Gibby, A. von Kienlin, R. M. Kippen, S. McBreen, B. Mailyan, C. A. Meegan, W. S. PaciesasO. Roberts, L. Sparke, M. Stanbro, K. Toelge, P. Veres

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With an instantaneous view of 70% of the sky, the Fermi Gamma-ray Burst Monitor (GBM) is an excellent partner in the search for electromagnetic counterparts to gravitational wave (GW) events. GBM observations at the time of the Laser Interferometer Gravitational-wave Observatory (LIGO) event GW150914 reveal the presence of a weak transient above 50 keV, 0.4~s after the GW event, with a false alarm probability of 0.0022 (2.9$\sigma$). This weak transient lasting 1 s was not detected by any other instrument and does not appear connected with other previously known astrophysical, solar, terrestrial, or magnetospheric activity. Its localization is ill-constrained but consistent with the direction of GW150914. The duration and spectrum of the transient event are consistent with a weak short Gamma-Ray Burst arriving at a large angle to the direction in which Fermi was pointing, where the GBM detector response is not optimal. If the GBM transient is associated with GW150914, this electromagnetic signal from a stellar mass black hole binary merger is unexpected. We calculate a luminosity in hard X-ray emission between 1~keV and 10~MeV of $1.8^{+1.5}_{-1.0} \times 10^{49}$~erg~s$^{-1}$. Future joint observations of GW events by LIGO/Virgo and Fermi GBM could reveal whether the weak transient reported here is a plausible counterpart to GW150914 or a chance coincidence, and will further probe the connection between compact binary mergers and short Gamma-Ray Bursts.
Original languageEnglish
JournalAstrophysical Journal Letters
Issue number1
Early online date11 Feb 2016
Publication statusPublished - 13 Jul 2016

Bibliographical note

Accepted for publication in ApJL


  • astro-ph.HE


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