Automating the Inclusion of Subthreshold Signal-to-Noise Ratios for\n Rapid Gravitational-Wave Localization

The accurate localization of gravitational-wave (GW) events in low-latency is\na crucial element in the search for further multimessenger signals from these\ncataclysmic events. The localization of these events in low-latency uses\nsignal-to-noise ratio (SNR) time-series from matched-filtered searches which\nidentify candidate events. Here we report on an improvement to the GstLAL-based\ninspiral pipeline, the low-latency pipeline that identified GW170817 and\nGW190425, which automates the use of SNRs from all detectors in the network in\nrapid localization of GW events. This improvement was incorporated into the\ndetection pipeline prior to the recent third observing run of the Advanced LIGO\nand Advanced Virgo detector network. Previously for this pipeline, manual\nintervention was required to use SNRs from all detectors if a candidate GW\nevent was below an SNR threshold for any detector in the network. The use of\nSNRs from subthreshold events can meaningfully decrease the area of the 90%\nconfidence region estimated by rapid localization. To demonstrate this, we\npresent a study of the simulated detections of $\\mathcal{O}(2\\times10^4)$\nbinary neutron stars using a network mirroring the second observational run of\nthe Advanced LIGO and Virgo detectors. When incorporating subthreshold SNRs in\nrapid localization, we find that the fraction of events that can be localized\ndown to $100~\\mathrm{deg}^2$ or smaller increases by a factor 1.18.\n