A hierarchical approach to targeted multi-messenger gravitational wave searches

We present a streamlined, externally triggered gravitational wave (GW) search for multi-messenger compact binary coalescence (CBC) events. Large or sub-threshold EM catalogs are good candidates for multi-messenger searches with LIGO-Virgo-KAGRA gravitational wave data but, depending on the telescope, can come with hundreds or thousands of events per year to follow up. PyGRB is the state-of-the-art modeled CBC multi-messenger search algorithm in LVK data. It is sensitive to quieter GW signals than the all-sky search for CBC events. However, it is computationally expensive, making it unsuited for large multi-messenger follow up efforts. We introduce a hierarchical search to process these large catalogs. This hierarchical approach uses time of arrival and sky location of an external trigger to identify potential signals in LVK data. Potential events are then passed to the more computationally costly deep analysis for acceptance or rejection. We use this approach to optimize the sensitivity of a followup search for GW associated with astrophysical events. We present our method, demonstrate its potential to identify events, and discuss its future applications.