TITLE: GCN CIRCULAR NUMBER: 42426 SUBJECT: GRB 251024A: Swift detection of a burst DATE: 25/10/24 18:09:58 GMT FROM: K.L. Page at U Leicester <klp5@leicester.ac.uk> M. J. Moss (GSFC), S. Dichiara (PSU), R. A. J. Eyles-Ferris (U Leicester), R. Gupta (NASA GSFC), J. A. Kennea (PSU), A. Y. Lien (U Tampa), K. L. Page (U Leicester) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 17:47:02.25 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 251024A (trigger= 1406589). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 306.622, -68.574 which is RA(J2000) = 20h 26m 29s Dec(J2000) = -68d 34' 25" 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 30 sec. The peak count rate was ~1000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 17:49:11.3 UT, 129.1 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 306.59743, -68.57225 which is equivalent to: RA(J2000) = 20h 26m 23.38s Dec(J2000) = -68d 34' 20.1" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 32 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 (3.73 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 3 (+2.09/-1.77) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 132 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 0.044. Burst Advocate for this burst is M. J. Moss (mikejmoss3 AT gmail.com). 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/42426. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...