Searches for Modulated {\gamma}-Ray Precursors to Compact Binary Mergers in Fermi-GBM Data

TL;DR

This paper develops a targeted search method for detecting modulated gamma-ray precursors to compact binary mergers in Fermi-GBM data, but finds no significant signals in the analyzed events.

Contribution

It introduces a novel method to identify modulated gamma-ray precursors based on expected time-dependent signals, applied to LIGO/Virgo GW events.

Findings

No significant gamma-ray precursor signals detected

Method sensitivity assessed with simulated signals

Applied to O2 and O3 LIGO/Virgo data without positive detections

Abstract

GW170817 is the only gravitational-wave (GW) event, for which a confirmed {\gamma}-ray counterpart, GRB 170817A, has been detected. Here we present a method to search for another type of {\gamma}-ray signal, a {\gamma}-ray burst precursor, associated with a compact binary merger. If emitted shortly before the coalescence, a high-energy electromagnetic (EM) flash travels through a highly dynamical and relativistic environment, created by the two compact objects orbiting each other. Thus, the EM signal arriving at an Earth observer could present a somewhat predictable time-dependent modulation. We describe a targeted search method for lightcurves exhibiting such a modulation, parameterized by the observer-frame component masses and binary merger time, using Fermi-GBM data. The sensitivity of the method is assessed based on simulated signals added to GBM data. The method is then applied to a selection of potentially interesting compact binary mergers detected during the second (O2) and third (O3) observing runs of Advanced LIGO and Advanced Virgo. We find no significant modulated {\gamma}-ray precursor signal associated with any of the considered events.