Fermi-GBM follow-up of the first gravitational-wave detection

The Advanced LIGO detectors made the first direct detection of gravitational-waves (GW) on September 14 2015 by observing the characteristic signal from a merger of two black holes, about 30 solar masses each and at a distance of 410 Mpc. The Fermi Gamma-ray Burst Monitor (GBM) covered 75% of the likely sky position of the source, and while no nearby GBM trigger was generated on-board in response to any bright gamma-ray burst (GRB), an automated offline pipeline designed to detect sub-threshold signals identified a weak event of moderate significance beginning 0.4s after the GW coalescence time and lasting for 1s. We discuss the initial detection and follow-up of the GBM event, including its plausibility as an EM counterpart when none is expected for the binary black-hole system observed. More generally, we discuss the ability for Fermi-GBM to find, characterize, and localize high-energy counterparts to GWs in the advanced LIGO era. In the coming years, detections and upper limits by Fermi-GBM for binary coalescence events involving a neutron star should reveal the progenitor behind short GRBs, aid in coordinating other targeted EM follow-up, and provide details about burst energetics and beaming.