TITLE: GCN CIRCULAR NUMBER: 45713 SUBJECT: GRB 260924A: Swift detection of a burst DATE: 26/09/24 01:41:46 GMT FROM: Jimmy DeLaunay at PSU V. D'Elia (SSDC & INAF-OAR), J. J. DeLaunay (PSU), R. Gupta (NASA GSFC), A. Y. Lien (U Tampa), K. L. Page (U Leicester), D. M. Palmer (LANL), T. M. Parsotan (GSFC) and B. Sbarufatti (INAF-OAB) report on behalf of the Neil Gehrels Swift Observatory Team: At 01:13:28 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 260924A (trigger=1513082). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec (133.740, +12.046) which is RA(J2000) = 08h 54m 58s Dec(J2000) = +12d 02' 44" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The available BAT light curve (cut off at T+8s while still active) showed a complex structure with a duration of at least 20 sec. The peak count rate was ~3700 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 01:15:18.8 UT, 110.6 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 133.7620, 12.0455 which is equivalent to: RA(J2000) = 08h 55m 2.88s Dec(J2000) = +12d 02' 43.8" with an uncertainty of 5.1 arcseconds (radius, 90% containment). This location is 77 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. UVOT took a finding chart exposure of 150 seconds with the White filter starting 123 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 0.041. Burst Advocate for this burst is V. D'Elia (valerio.delia AT ssdc.asi.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/)