TITLE: GCN CIRCULAR NUMBER: 41152 SUBJECT: GRB 250725A: Swift detection of a burst DATE: 25/07/25 02:16:19 GMT FROM: K.L. Page at U Leicester <klp5@leicester.ac.uk> P. A. Evans (U Leicester), N. P. M. Kuin (UCL-MSSL), K. L. Page (U Leicester) and D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift Observatory Team: At 01:51:36 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250725A (trigger=1336720). Swift slewed to the burst after a short delay due to an observing constraint. The BAT on-board calculated location is RA, Dec 35.385, -82.784 which is RA(J2000) = 02h 21m 32s Dec(J2000) = -82d 47' 02" 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 20 sec. The peak count rate was ~8700 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 02:03:56.8 UT, 740.4 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 35.47808, -82.79131 which is equivalent to: RA(J2000) = 02h 21m 54.74s Dec(J2000) = -82d 47' 28.7" with an uncertainty of 3.5 arcseconds (radius, 90% containment). This location is 49 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (9.21 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.9 (+2.24/-1.95) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 879 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 100% of the XRT 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 XRT 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 0.115. Burst Advocate for this burst is P. A. Evans (pae9 AT leicester.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/) View this GCN Circular online at https://gcn.nasa.gov/circulars/41152. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...