TITLE: GCN CIRCULAR NUMBER: 41848 SUBJECT: GRB 250917B: Swift detection of a short burst DATE: 25/09/17 06:48:14 GMT FROM: K.L. Page at U Leicester <klp5@leicester.ac.uk> R. Caputo (GSFC), C. Gronwall (PSU) and K. L. Page (U Leicester) report on behalf of the Neil Gehrels Swift Observatory Team: At 06:27:44 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250917B (trigger=1350381). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 291.378, +11.113 which is RA(J2000) = 19h 25m 31s Dec(J2000) = +11d 06' 48" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a short, single peaked structure with a duration of about 0.5 sec. The peak count rate was ~8000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 06:29:58.5 UT, 134.2 seconds after the BAT trigger. No source was detected in 681 s of promptly downlinked data. We are waiting for the full dataset to detect and localise the XRT counterpart. UVOT took a finding chart exposure of 150 seconds with the White filter starting 138 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 25% of the BAT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the BAT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the large, but uncertain, extinction expected. Burst Advocate for this burst is R. Caputo (regina.caputo AT nasa.gov). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/41848. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...