Gamma-Ray Bursts in the Multi-Messenger Era

Gamma-ray Bursts (GRBs) are incredibly energetic, brief flashes of gamma-rays originating from some of the most violent explosions in the universe. The progenitors of the two main classes GRBs, long and short, are thought to be the core collapse of massive stars for long GRBs and the merger of compact objects, like neutron stars and black holes for short GRBs. Though the emission for either class is still not perfectly understood, long GRBs are more well-understood due to their larger energy output and brighter afterglows. The first ever high-energy multi-messenger detection occurred on August 17th, 2017 when a short GRB was observed in coincidence with gravitational waves originating from two neutron stars merging into each other in a galaxy over one hundred million light-years away. This observation had wide spread scientific implications, including the confirmation as compact object mergers as short GRB progenitors, but one surprising result was the lowest measured luminosity of a short GRB by more than 2 orders of magnitude. The revelation of this new population of low-luminosity short GRBs motivates sensitive GRB searches to find and study other members of the population. This dissertation focuses on work I have done using data from Swift's Burst Alert Telescope (BAT) as a tool for multi-messenger astrophysics. This includes a targeted analysis using existing tools to search for counterparts to astrophysical events of interest, and a new likelihood-based method of analyzing BAT data I developed to make a more sensitive search for GRBs. This new likelihood-based search is capable of increasing the detection horizon of a GRB 170817A-like burst by ~50% compared to the onboard analysis. I will also discuss the results of these searches, including the arcminute-scale localization of 8 GRBs that were not detected onboard BAT