TITLE: GCN CIRCULAR NUMBER: 41714 SUBJECT: GRB 250905A: Swift detection of a burst DATE: 25/09/05 02:25:34 GMT FROM: David Palmer at LANL <palmer@lanl.gov> R. Brivio (INAF-OAB), S. Dichiara (PSU), D. M. Palmer (LANL), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 02:09:54 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250905A (trigger=1347265). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 233.047, +0.777 which is RA(J2000) = 15h 32m 11s Dec(J2000) = +00d 46' 39" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). Due to a telemetry gap, the BAT lightcurve is not immediately available. The XRT began observing the field at 02:12:11.4 UT, 136.6 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 233.00629, 0.79395 which is equivalent to: RA(J2000) = 15h 32m 01.51s Dec(J2000) = +00d 47' 38.2" with an uncertainty of 3.4 arcseconds (radius, 90% containment). This location is 158 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. We cannot determine whether the source is fading at the present time. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 5.50 x 10^20 cm^-2 (Willingale et al. 2013). UVOT took a finding chart exposure of 150 seconds with the White filter starting 140 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 none of the XRT error circle. 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 0.054. Burst Advocate for this burst is R. Brivio (riccardo.brivio AT inaf.it). 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/41714. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...