TITLE: GCN CIRCULAR NUMBER: 41110 SUBJECT: GRB 250717B: Swift/BAT-GUANO arcminute localization of a burst DATE: 25/07/17 16:46:46 GMT FROM: Samuele Ronchini at PSU sjs8171@psu.edu
Samuele Ronchini (PSU), James DeLaunay (PSU), Aaron Tohuvavohu (Caltech), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (PSU) report:
Swift/BAT did not localize GRB 250717B onboard (T0: 2025-07-17T13:44:22 UTC, Fermi GCN 41107).
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 the newly developed pipeline BAT-GLIMPSE: Gamma-ray Localization using Imaging and Mosaic techniques for Pointing and Slew Epochs (Ronchini et. al, in prep). The pipeline makes use of the tools from BatAnalysis ([Parsotan et al. 2025](https://iopscience.iop.org/article/10.3847/1538-4357/ade240)). The source is found with an SNR = 26.3.
The BAT position is:
RA, Dec = 44.1179, 26.3789 deg which is
RA(J2000) = 02h 56m 28.30s
Dec(J2000) = 26d 22’ 44.0″
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=774452698
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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