GRB 241213A: Swift detection of a burst

At 02:19:00 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 241213A (trigger=1274039). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 116.148, +35.280 which is RA(J2000) = 07h 44m 35s Dec(J2000) = +35d 16' 49" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a bright peak with a duration of about 15 sec. The peak count rate was ~9500 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 02:25:36.0 UT, 395.9 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 116.17145, 35.27944 which is equivalent to: RA(J2000) = 07h 44m 41.15s Dec(J2000) = +35d 16' 46.0" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 68 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 (6.66 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 5 (+2.07/-1.84) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 250 seconds with the U filter starting 318 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 none of the XRT error circle. 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 18.0 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.060. Burst Advocate for this burst is R. Gupta (rahulbhu.c157 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/)