TITLE: GCN CIRCULAR NUMBER: 35314 SUBJECT: GRB 231210B: Swift detection of a burst with optical counterpart DATE: 23/12/10 21:49:47 GMT FROM: Jamie Kennea at Penn State <jak51@psu.edu> K. L. Page (U Leicester), J.D. Gropp (PSU), J. A. Kennea (PSU), D. M. Palmer (LANL), T. M. Parsotan (GSFC/UMBC/CRESSTII) and M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 21:29:04 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 231210B (trigger=1201696). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 95.772, -48.359 which is RA(J2000) = 06h 23m 05s Dec(J2000) = -48d 21' 32" 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 15 sec. However, since this GRB occurred while the spacecraft was leaving the SAA, the rate lightcurve is hard to interpret. The peak count rate was ~1500 counts/sec (15-350 keV), at ~T+0 sec after the trigger. The XRT began observing the field at 21:31:07.8 UT, 123.4 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source with an enhanced position: RA, Dec 95.79386, -48.37201 which is equivalent to: RA(J2000) = 06h 23m 10.53s Dec(J2000) = -48d 22' 19.2" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 70 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. The initial flux in the 2.5 s image was 4.31e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 462 seconds after the BAT trigger. Due to tracking issues, the UVOT image is blurred. However, comparison with DSS shows that there appears to be a new source coincident with the XRT localization. Further data and analysis will be needed to report an accurate localization and magnitude of this object. Burst Advocate for this burst is K. L. Page (klp5 AT leicester.ac.uk). 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/35314. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...