GRB 241006A: Swift detection of a burst

At 21:51:58 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 241006A (trigger=1258721). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 304.794, -40.796 which is RA(J2000) = 20h 19m 11s Dec(J2000) = -40d 47' 44" 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 30 sec. The peak count rate was ~700 counts/sec (15-350 keV), at ~-1 sec after the trigger. The XRT began observing the field at 21:54:23.5 UT, 145.3 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source with an enhanced position: RA, Dec 304.74258, -40.80514 which is equivalent to: RA(J2000) = 20h 18m 58.22s Dec(J2000) = -40d 48' 18.5" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 143 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. We cannot determine whether the source is fading at the present time. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (4.92 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.5 (+3.24/-2.77) x 10^21 cm^-2 (90% confidence). The initial flux in the 2.5 s image was 4.75e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 349 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 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.065. 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/)