TITLE: GCN CIRCULAR NUMBER: 32167 SUBJECT: GRB 220606B: Swift/BAT-GUANO candidate arcminute localization of a short burst DATE: 22/06/06 12:23:36 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 220606B onboard (T0: 2022-06-06T01:03:28 UTC, Fermi/GBM GCN 32165). 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 0.512 s analysis time bin with a sqrt(TS) of 10.7. The duration of the burst as seen by BAT is less than 0.5 s. A candidate arcminute localization is found with DeltaLLHOut of 11.3 and a DeltaLLHPeak of 3.1. 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. See Section 9.1 and Figure 20 in the NITRATES paper for brief descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut. The BAT position is RA, Dec = 28.474, -54.471 deg which is RA(J2000) = 01h 53m 53.76s Dec(J2000) = -54d 28′ 15.6″ with an estimated uncertainty of 5 arcmin. This position is consistent with the Fermi/GBM localization (GCN 32165). 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/