Search for advanced LIGO single interferometer compact binary coalescence signals in coincidence with Gamma-ray events in Fermi-GBM

Abstract

Presented is the description of a new and general method used to search for γ-ray counterparts to gravitational-wave (GW) triggers. This method is specifically applied to single GW detector triggers. Advanced LIGO data from observing runs O1 and O2 were analyzed, thus each GW trigger comes from either the LIGO-Livingston or the LIGO-Hanford interferometer. For each GW trigger, Fermi Gamma-ray Burst Monitor data is searched and the most significant subthreshold signal counterpart is selected. Then, a methodology is defined in order to establish which of GW-γ-ray pairs are likely to have a common origin. For that purpose an association ranking statistic is calculated from which a false alarm rate is derived. The events with the highest ranking statistics are selected for further analysis consisting of LIGO detector characterization and parameter estimation. The γ-ray signal characteristics are also evaluated. We find no significant candidates from the search.

A Joint Fermi-GBM and LIGO/Virgo Analysis of Compact Binary Mergers from the First and Second Gravitational-wave Observing Runs

“…the reweighted S/N of the GW trigger, (iii) the Targeted Search Λ, and (iv) the overlap between the GW and gamma-ray sky localizations defined in Ashton et al (2018). Further details on the statistical method will be given in Stachie et al (2020). Although we find no highly significant associations, a close inspection of the data around the 80 candidates with the highest significance (i.e.…”

“…A single L1 surviving coincident association remained with no obvious reason for rejection. However, the derived FAR, based on coincidences between noises in LIGO and noises in GBM (Stachie et al 2020), is relatively high at 1.1×10 −6 Hz. The implied low significance is mainly due to the soft spectrum of the GBM candidate.…”

“…This is done by incorporating the probability that each CBC candidate originated from an astrophysical rather than terrestrial source and also considering the fraction of LIGO/Virgo localization probability that was observable to GBM at GW trigger time. Finally, we augment GBM follow-up of GW events by also reporting results from a new search method (Stachie et al 2020) that seeks gamma-rays coincident with LIGO single-interferometer triggers.…”

A Joint Ranking Statistic for Multi-messenger Astronomical Searches with Gravitational Waves

“…The joint ranking statistic of interest here will be the odds ratio between whether two candidates are truly correlated (H c ), meaning they have the same underlying shared parameters θ [23], or whether they are uncorrelated (H uncor ), meaning the association is from random chance. To understand the uncorrelated hypothesis as described in Stachie et al [17], let us first consider a single isolated astrophysical event candidate. This candidate has only a couple of possibilities for its origin: either this event is from the intended astrophysical source (H s ) or is an artifact of noise (H n ), instrumental or otherwise.…”

“…This work is meant to be a Bayesian derivation of the odds ratio for whether two events are correlated (real coincidence) versus non-correlated (random coincidence), primarily based on the results of Ashton et al [23] and Stachie et al [17] while similarly applying this method specifically to GW-GRB coincidences. We note that other Bayesian approaches have been developed for multi-messenger searches in the context of GWneutrino bursts [25,26].…”