TITLE: GCN CIRCULAR NUMBER: 31541 SUBJECT: GRB 220131B: Swift/BAT-GUANO detection outside the coded FOV DATE: 22/02/01 18:46:38 GMT FROM: Aaron Tohuvavohu at U Toronto Aaron Tohuvavohu (U Toronto), Gayathri Raman (PSU), James DeLaunay (UAlabama), Jamie A. Kennea (PSU), report: Swift/BAT did not localize GRB 220131B onboard (T0: 2022-01-31T01:09:16.7 UTC, GECAM GCN 31534). The GECAM notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1). Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 90 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground. The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu, arXiv:2111.01769), detects the burst with a sqrt(TS) of 9.2 in a 2.048 s analysis time bin. NITRATES results are consistent with a burst coming from outside the coded FOV, with DeltaLLHOut of 1.9. The best fit sky position from NITRATES is consistent with the GECAM localization within the stated error (GCN 31534). See Section 9.1 and Figure 20 in the NITRATES paper for brief descriptions and interpretation of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut. GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches. A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/