TITLE: GCN CIRCULAR NUMBER: 31160 SUBJECT: GRB 211203A: Swift detection of a burst DATE: 21/12/03 09:33:20 GMT FROM: Phil Evans at U of Leicester P. A. Evans (U Leicester), S. Dichiara (PSU), J.D. Gropp (PSU) and K. L. Page (U Leicester) report on behalf of the Neil Gehrels Swift Observatory Team: At 09:02:38 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 211203A (trigger=1086826). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 170.174, +16.256 which is RA(J2000) = 11h 20m 42s Dec(J2000) = +16d 15' 21" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 25 sec. The peak count rate was ~3000 counts/sec (15-350 keV), at ~7 sec after the trigger. The XRT began observing the field at 09:03:56.8 UT, 78.5 seconds after the BAT trigger. No source was detected in 2 s of promptly downlinked data, which covered 93% of the BAT error circle. 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 81 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 expected extinction corresponding to E(B-V) of 0.023. Burst Advocate for this burst is P. A. Evans (pae9 AT star.le.ac.uk). 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/)