Searching for gravitational waves from compact binary mergers powering long gamma-ray bursts during LIGO-Virgo-KAGRA's O3 run

TL;DR

The paper investigates whether some long gamma-ray bursts originate from compact binary mergers by performing a targeted, template-based gravitational-wave search in LVK O3 data around long GRBs detected by Fermi/GBM and Swift/BAT. It employs a Bayesian framework with the Bayes coherence ratio to compare coherent versus incoherent evidences for sub-threshold BNS/NSBH signals, using fixed EM sky positions and a short coalescence-time window around each GRB. No coincident gravitational-wave signals are found; the study places per-event luminosity-distance limits and derives a population-level constraint on $f$, the fraction of long GRBs powered by mergers, which remains uninformative given current sensitivity. The results demonstrate the utility of EM localizations to enhance GW searches, but indicate that a substantial increase in sensitive volume (e.g., with Cosmic Explorer) is required to meaningfully constrain or detect a merger-powered long GRB population, with plans to apply the approach to LVK O4 data.

Abstract

Neutron star binary mergers are often associated with short gamma-ray bursts (GRBs), but the recent detection of kilonovae coincident with long GRBs suggest that some mergers may produce long GRBs. Motivated by these developments, we perform a search for binary neutron star and neutron star-black hole gravitational-wave signals coincident with long GRBs using data from the third LIGO--Virgo--KAGRA (LVK) observing run. We analyze LVK data coincident with long GRBs detected by Fermi's GRB Monitor and Swift's Burst Alert Telescope when at least two gravitational-wave observatories were running. We find no evidence of a coincident gravitational-wave signal and set limits on the luminosity distance to each of these long GRBs under the assumption that they were powered by binary mergers.

Figures (3)

• Figure 1: The distribution of Bayesian coherence ratio (BCR). The distribution for long GRBs coincident with HLV data is shown in blue, the distribution for long GRBs coincident with HL data is shown in orange, and the distribution of off-source data (with no long GRB trigger) is shown in green. The BCR of a recent HL sub-threshold binary neutron-star merger candidate GW231109_235456 niu2025gw231109235456subthresholdbinaryneutron is shown by the maroon vertical line.
• Figure 2: The Bayesian coherence ratio (blue) for a set of injected signals into a three-detector network (HLV) with varying luminosity distance, as described in Section \ref{['sec:test_case']}. The background threshold, corresponding to the maximum off-source $\log_{10}(\mathrm{BCR})=2.8$ value, for a positive identification is shown in green. The BCR may provide evidence for sub-threshold events with network optimal SNR $\approx8-12$.
• Figure 3: Estimated posterior distribution of $f$, the fraction of gravitationally-bright long GRBs originating from binary mergers. The blue curve shows constraints obtained using the current sensitive search volume, the purple curve assumes a 500-fold increase in sensitive volume, and the orange curve corresponds to a next-generation detector, Cosmic Explorer, under the assumption of no coincident long GRB and gravitational-wave detections, as described in Section \ref{['sec:fraction']}. We can then constrain $f$ to an upper limit of 0.90, 0.62, and 0.00 with $90\%$ credibility, respectively. The shaded region plots the uncertainty from the rate of gravitationally-bright GRBs, $R = \unit[79^{+57}_{-33}]{Gpc^{-3}yr^{-1}}$.