Fermi-LAT observations of the LIGO/Virgo event GW170817

TL;DR

This paper reports on Fermi-LAT observations of the neutron star merger GW170817, setting upper limits on high-energy gamma-ray emission on various timescales, and discusses future detection prospects.

Contribution

It provides the first constraints on high-energy gamma-ray emission from GW170817 over extended timescales using Fermi-LAT data.

Findings

No high-energy gamma-ray emission detected post-merger

Established flux upper bounds in the 0.1-1 GeV range

Compared luminosity limits to other short gamma-ray bursts

Abstract

We present the Fermi Large Area Telescope (LAT) observations of the binary neutron star merger event GW170817 and the associated short gamma-ray burst (SGRB) GRB\,170817A detected by the Fermi Gamma-ray Burst Monitor. The LAT was entering the South Atlantic Anomaly at the time of the LIGO/Virgo trigger ($t_{\rm GW}$) and therefore cannot place constraints on the existence of high-energy (E $>$ 100 MeV) emission associated with the moment of binary coalescence. We focus instead on constraining high-energy emission on longer timescales. No candidate electromagnetic counterpart was detected by the LAT on timescales of minutes, hours, or days after the LIGO/Virgo detection. The resulting flux upper bound (at 95\% C.L.\/) from the LAT is $4.5\times$10$^{-10}$ erg cm$^{-2}$ s$^{-1}$ in the 0.1--1 GeV range covering a period from T0 + 1153 s to T0 + 2027 s. At the distance of GRB\,170817A, this flux upper bound corresponds to a luminosity upper bound of 9.7$\times10^{43}$ erg s$^{-1}$, which is 5 orders of magnitude less luminous than the only other LAT SGRB with known redshift, GRB\,090510. We also discuss the prospects for LAT detection of electromagnetic counterparts to future gravitational wave events from Advanced LIGO/Virgo in the context of GW170817/GRB\,170817A.