# Potential Gravitational-wave and Gamma-ray Multi-messenger Candidate from Oct. 30, 2015

## TL;DR

This paper introduces a new combined ranking method to enhance detection of joint gravitational-wave and gamma-ray signals from neutron star mergers, identifying a promising candidate from 2015 with a 25% chance of being astrophysical.

## Contribution

The study presents a novel combined ranking statistic that increases joint detection sensitivity by 70%, leading to the identification of a potential neutron star merger candidate from 2015.

## Key findings

- Identified one candidate with a false alarm rate of 1 in 13 years.
- Estimated the candidate's distance at approximately 187 Mpc.
- Calculated a 25% probability that the candidate is of astrophysical origin.

## Abstract

We present a search for binary neutron star mergers that produced gravitational-waves during the first observing run of Advanced LIGO and gamma-ray emission seen by either \textit{Swift}-BAT or Fermi-GBM, similar to GW170817 and GRB 170817A. We introduce a new method using a combined ranking statistic to detect sources that do not produce significant gravitational-wave or gamma-ray burst candidates individually. The current version of this search can increase by 70% the detections of joint gravitational-wave and gamma-ray signals. We find one possible candidate observed by LIGO and Fermi-GBM, 1-OGC 151030, at a false alarm rate of 1 in 13 years. If astrophysical, this candidate would correspond to a merger at $187^{+99}_{-87}\,$Mpc with source-frame chirp mass of $1.30^{+0.02}_{-0.03}\,\mathrm{M}_{\odot}$. If we assume the viewing angle must be $<30^{\circ}$ to be observed by \textit{Fermi}-GBM, our estimate of the distance would become $224^{+88}_{-78}\,$Mpc. By comparing the rate of binary neutron star mergers to our search-estimated rate of false alarms, we estimate that there is a 1 in 4 chance this candidate is astrophysical in origin.