Using Archival VERITAS Data to Search for Counterparts to Sub-Threshold Neutron-Star Merger Candidates

During Advanced LIGO's first observing run, which ran from September 2015 to January 2016, the detector confidently detected three binary black hole mergers in gravitational waves (GWs) and no binary neutron star (BNS) mergers. However, in a post-factum analysis, 103 sub-threshold BNS merger candidates were identified. The first confidently detected BNS merger was not measured until the subsequent observing season, but, notably, this event was also associated with an electromagnetic counterpart extending up to low-energy (LE; 100 keV - 100 MeV) gamma rays. The association of such an event at even higher energies, like those probed by imaging atmospheric Cherenkov telescope (IACT) arrays remains an open question. In this contribution, I will describe a study performed using archival data from the VERITAS IACT array to search for transient events in very-high-energy (VHE; > 100 GeV) gamma rays motivated by the sub-threshold BNS merger candidates from LIGO's first observing run. I will present the results from this study, and further describe the promise of this technique for joint sub-threshold searches with current- and future-generation IACT arrays.