TITLE: GCN CIRCULAR NUMBER: 28583 SUBJECT: GRB 201008A: Swift/BAT-GUANO detection and possible arcminute localization DATE: 20/10/08 22:41:45 GMT FROM: James DeLaunay at PSU James DeLaunay (PSU), Aaron Tohuvavohu (U Toronto), Jamie Kennea (PSU), Peter Veres (UAH) report: Swift/BAT did not trigger on GRB 201008A (T0: 2020-10-08 10:37:36 UTC, Fermi/GBM Team TRIGGER 623846261). The Fermi/GBM 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 burst is detected in BAT with a T90 duration of ~2.5 seconds. With a maximum likelihood analysis (DeLaunay et al. 2020, in prep.) on the event-mode data we detect a location for the burst with a square root of the test statistic, sqrt(TS), of 13.22. The sqrt(TS) behaves similarly to SNR. Using the normal BAT imaging technique, we find the location of the GRB with an SNR of 4.2. Since this is a low significance detection near the edge of the coded field of view there is a chance that this localization may be incorrect. The BAT ground-calculated position is RA, Dec = 161.744, 46.101 deg which is RA(J2000) = 10h 46m 58.56s Dec(J2000) = 46d 06’ 03.6” with an uncertainty of 5 arcmin, (radius, sys+stat, 90% containment). The partial coding was 3.5%. This position is consistent with the Fermi GBM localization ( https://gcn.gsfc.nasa.gov/other/623846261.fermi) and BALROG localization (GCN 28577). XRT and UVOT follow-up has been triggered. 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/