TITLE: GCN CIRCULAR NUMBER: 36536 SUBJECT: GRB 240523A: Swift detection of a burst DATE: 24/05/23 15:02:52 GMT FROM: David Palmer at LANL <palmer@lanl.gov> M. H. Siegel (PSU), J.D. Gropp (PSU), R. Gupta (NASA/GSFC), J. A. Kennea (PSU), N. J. Klingler (GSFC/UMBC/CRESSTII), H. A. Krimm (NSF), K. L. Page (U Leicester), D. M. Palmer (LANL) and M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 14:43:11 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 240523A (trigger=1230423). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 33.567, -22.020 which is RA(J2000) = 02h 14m 16s Dec(J2000) = -22d 01' 12" 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 40 sec. The peak count rate was ~800 counts/sec (15-350 keV), at ~-1 sec after the trigger. The XRT began observing the field at 14:45:39.6 UT, 147.7 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 33.56813, -22.03320 which is equivalent to: RA(J2000) = 02h 14m 16.35s Dec(J2000) = -22d 01' 59.5" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 47 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. No spectrum from the promptly downlinked event data is yet available to determine the column density. UVOT took a finding chart exposure of 150 seconds with the White filter starting 151 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 100% 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 0.015. Burst Advocate for this burst is M. H. Siegel (siegel AT swift.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/) View this GCN Circular online at https://gcn.nasa.gov/circulars/36536. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...