TITLE: GCN CIRCULAR NUMBER: 40600 SUBJECT: GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst DATE: 25/06/01 22:21:42 GMT FROM: Samuele Ronchini at PSU sjs8171@psu.edu
James DeLaunay (PSU), Samuele Ronchini (PSU), Aaron Tohuvavohu (Caltech), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report:
Swift/BAT did not localize GRB 250601A onboard (T0: 2025-06-01T17:29:35.54 UTC, Fermi GCN 40596).
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 position is found with standard imaging, with an SNR = 8.7. The duration of the burst is ~1 sec.
The BAT position is
RA, Dec = 90.0709, -57.2892 deg which is
RA(J2000) = 06h 00m 17.02s
Dec(J2000) = -57d 17’ 21.1″
with an estimated uncertainty of 3 arcmin radius.
More details about this burst can be found on the trigger report page here: https://guano.swift.psu.edu/trigger_report?id=770491811
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/
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