A hierarchical approach to multi-messenger gravitational wave searches*

We introduce a streamlined, externally triggered gravitational wave (GW) search for multi-messenger compact binary coalescence events. Telescopes with large or sub-threshold catalogs are good candidates for multi-messenger searches with LIGO-Virgo-KAGRA GW data but can come with thousands of events per year to follow up. PyGRB, the state-of-the-art CBC multi-messenger search algorithm, is sensitive but computationally expensive, processing only ~100 events per year at 2 or more weeks of wall time each. This makes it unsuited for large multi-messenger follow up efforts. We introduce a hierarchical search algorithm, PyNu, to process these large catalogs to pass potential coincident events to PyGRB for follow-up. Our algorithm is based in PyCBC, a Python-based GW search package used by the LVK to identify events in GWTC-3. In our hierarchical approach, we use a trigger's time of arrival and sky location to identify potential signals in LVK data, cutting down large catalogs to only "interesting" potential coincidences. Events that are sufficiently interesting are then passed to PyGRB for acceptance or rejection. In this talk we present PyNu's method, demonstrate its sub-1-hour runtime and potential to identify events using GW170817, and discuss its future applications.