A Fermi Gamma-ray Burst Monitor Search for Electromagnetic Signals Coincident with Gravitational-Wave Candidates in Advanced LIGO's First Observing Run

TL;DR

This study searched for gamma-ray signals coincident with gravitational wave events from LIGO's first run using Fermi GBM, finding no significant associations but providing constraints on electromagnetic counterparts.

Contribution

First comprehensive search for gamma-ray counterparts to LIGO O1 GW candidates using Fermi GBM data, including both blind and targeted analyses.

Findings

No coincident gamma-ray signals detected with GW candidates.

Identified two GBM events with low false alarm rates, one being a known solar flare.

Provided upper limits on gamma-ray emission associated with GW events.

Abstract

We present a search for prompt gamma-ray counterparts to compact binary coalescence gravitational wave (GW) candidates from Advanced LIGO's first observing run (O1). As demonstrated by the multimessenger observations of GW170817/GRB 170817A, electromagnetic and GW observations provide complementary information about the astrophysical source and, in the case of weaker candidates, may strengthen the case for an astrophysical origin. Here we investigate low-significance GW candidates from the O1 compact-binary coalescence searches using the Fermi Gamma-ray Burst Monitor (GBM), leveraging its all-sky and broad energy coverage. Candidates are ranked and compared to background to measure significance. Those with false alarm rates of less than 10^-5 Hz (about one per day) are used as the search sample for gamma-ray follow-up. No GW candidates were found to be coincident with gamma-ray transients independently identified by blind searches of the GBM data. In addition, GW candidate event times were followed up by a separate targeted search of GBM data. Among the resulting GBM events, the two with lowest false alarm rates were the gamma-ray transient GW150914-GBM presented in Connaughton et al. (2016) and a solar flare in chance coincidence with a GW candidate.