Optimal Follow-Up of Gravitational-Wave Events with the UltraViolet EXplorer (UVEX)

The UltraViolet EXplorer (UVEX) is a wide-field, all-sky, time-domain, ultraviolet survey space telescope selected as a NASA Medium-Class Explorer (MIDEX) mission for launch in 2030. UVEX will conduct an unprecedented all-sky time-domain survey in two ultraviolet (UV) filters. UVEX will follow up gravitational wave (GW) binary neutron star mergers as targets of opportunity (ToOs), rapidly scanning across their localization regions to search for their kilonova (KN) counterparts. Early-time multiband ultraviolet light curves of KNe are key to explaining the interplay between jet and ejecta in binary neutron star mergers. Owing to high Galactic extinction in the ultraviolet and UVEX’s large field of view (FOV), variation in sensitivity across the GW region of interest (ROI) is an important consideration for observation planning. We present an optimal strategy for GW follow-up with UVEX in which exposure time is adjusted dynamically for each field individual to maximize the overall probability of detection. We have implemented this strategy in an open source astronomical scheduling toolkit called the Multi-Mission Multi-Messenger Observation Planning Toolkit (M4OPT), on GitHub at https://github.com/m4opt/m4opt.