GRB 240516A: Swift detection of a burst

At 03:36:28 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 240516A (trigger=1228797). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 212.770, -63.505 which is RA(J2000) = 14h 11m 05s Dec(J2000) = -63d 30' 17" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of at least 20 sec. The peak count rate was ~1400 counts/sec (15-350 keV), at ~1 sec after the trigger. The XRT began observing the field at 03:38:50.4 UT, 142.1 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 212.8071, -63.4878 which is equivalent to: RA(J2000) = 14h 11m 13.70s Dec(J2000) = -63d 29' 16.1" with an uncertainty of 6.1 arcseconds (radius, 90% containment). This location is 85 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 2 seconds with the White filter starting 150 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. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the sub-image. Results from the list of sources generated on-board are not available at this time. No correction has been made for the large, but uncertain, extinction expected. Burst Advocate for this burst is T. M. Parsotan (parsotat AT umbc.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/)