TITLE: GCN CIRCULAR NUMBER: 31746 SUBJECT: GRB 220310C: Swift/BAT-GUANO candidate arcminute localization DATE: 22/03/11 20:30:38 GMT FROM: Aaron Tohuvavohu at U Toronto Aaron Tohuvavohu (U Toronto), James DeLaunay (UAlabama), Gayathri Raman (PSU), Jamie A. Kennea (PSU), report: Swift/BAT did not localize GRB 220310C onboard (T0: 2022-03-10T22:23:51 UTC, Fermi/GBM GCN 31735). The Fermi 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 200 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 in a 8.192 s analysis time bin with a sqrt(TS) of 9.7. A candidate arcminute localization is found with DeltaLLHOut of 19.7 and a DeltaLLHPeak of 5.7. For this reason we can confidently claim detection, and preference for an in FOV origin, but the best fit arcmin localization is not strongly preferred over other positions. A few burst locations with comparable DeltaLLHPeak have been previously verified with afterglow discovery (eg GRB 211106A). See Section 9.1 and Figure 20 in the NITRATES paper for brief descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut. No source is found with conventional BAT imaging. This is expected given the strength of the signal in BAT, and its position near the edge of the coded FOV. The BAT position is RA, Dec = 290.069, +40.253 deg which is RA(J2000) = 19h 20m 16.62s Dec(J2000) = +40d 15′ 12.3″ with an estimated uncertainty of 5 arcmin. This independent position is consistent with the Fermi/GBM localization (GCN 31735). XRT and UVOT follow-up has been requested. Results of follow-up observations will be reported in future circulars. 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/