A New Search Pipeline for Short Gamma-Ray Bursts in Fermi/GBM Data—A 50% Increase in the Number of Detections

In this paper, we present the development and the results of a new search pipeline for short gamma-ray bursts (sGRBs) in the publicly available data from the Gamma-Ray Burst Monitor (GBM) on board the Fermi satellite. This pipeline uses rigorous statistical methods that are designed to maximize the information extracted from the Fermi/GBM detectors. Our approach differs substantially from existing search efforts in several aspects: the pipeline includes the construction of template banks, Poisson matched filtering, background estimation, background misestimation correction, automatic routines to filter contaminants, statistical estimation of the signal location, and a quantitative estimator of the signal probability of being of cosmological, terrestrial, or solar origin. Our analysis also includes operating the pipeline on “time-slid” copies of the data, which allows exact significance assessment and p astro computation, akin to the state-of-the-art gravitational-wave (GW) data analysis pipelines. Depending on the spectral properties of the bursts, our pipeline achieves a signal-to-noise ratio improvement by a factor of 2–15 over the onboard GBM triggering algorithm. This enhancement increases the detectable volume for sGRBs and results in an approximately 50% increase in sGRB detections in the 2014 GBM data set. As a further consequence of the sensitivity increase, we detect hundreds of soft gamma-ray flares of Galactic origin. This improved sensitivity enhances the chances of detecting fainter, off-axis gamma-ray bursts that would likely fall below the standard triggering thresholds. Applying this pipeline to the full GBM archive is expected to expand further the joint sGRB–GW detection volume.