TITLE: GCN CIRCULAR NUMBER: 12391 SUBJECT: GRB 110924A: Swift detection of a possible burst DATE: 11/09/24 09:26:59 GMT FROM: Erik Hoversten at Swift/Penn State E. A. Hoversten (PSU), A. P. Beardmore (U Leicester), P. A. Evans (U Leicester), O. M. Littlejohns (U Leicester), C. Pagani (U Leicester), K. L. Page (U Leicester), B. Sbarufatti (INAF-OAB/IASFPA), E. Sonbas (GSFC/USRA/Adiyaman Univ.) and T. N. Ukwatta (MSU) report on behalf of the Swift Team: At 09:03:20 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 110924A (trigger=503926). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 234.748, -66.308 which is RA(J2000) = 15h 39m 00s Dec(J2000) = -66d 18' 29" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single peak structure with a duration of about 10 sec. The peak count rate was ~1500 counts/sec (15-350 keV), at ~1 sec after the trigger. The XRT began observing the field at 09:05:10.5 UT, 109.8 seconds after the BAT trigger. No source was detected in 729 s of promptly downlinked data. We are waiting for the full dataset to detect and localise the XRT counterpart. UVOT took a finding chart exposure of 150 seconds with the White filter starting 115 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 25% of the BAT 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 69% of the BAT 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 0.16. Burst Advocate for this burst is E. A. Hoversten (hoversten AT astro.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/too.html.)