TITLE: GCN CIRCULAR NUMBER: 30986 SUBJECT: GRB 211025A: Swift detection of a burst DATE: 21/10/25 05:29:36 GMT FROM: Aaron Tohuvavohu at U Toronto <aaron.tohu@gmail.com> J.D. Gropp (PSU), D. M. Palmer (LANL), B. Sbarufatti (PSU) and A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift Observatory Team: At 05:10:20 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 211025A (trigger=1081113). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 162.377, +31.557 which is RA(J2000) = 10h 49m 30s Dec(J2000) = +31d 33' 26" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is usual for an image trigger, the immediately available BAT lightcurve is unclear, but there does appear to be a peak between T+30 and T+64, with a peak count rate of ~300 counts/s (15-350 kev) at ~38 s after the nominal trigger time. The XRT began observing the field at 05:12:23.2 UT, 123.3 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 162.38427, 31.51343 which is equivalent to: RA(J2000) = 10h 49m 32.22s Dec(J2000) = +31d 30' 48.3" with an uncertainty of 4.1 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. No spectrum from the promptly downlinked event data is yet available to determine the column density. The initial flux in the 2.5 s image was 5.36e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 131 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image processing FAILED because of no aspect solution. Results from the list of sources generated on-board are not available at this time. No correction has been made for the expected extinction corresponding to E(B-V) of 0.027. Burst Advocate for this burst is J.D. Gropp (jdg44 AT psu.edu). 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/)