GCN Circular 35269

P. A. Evans (U Leicester), S. Dichiara (PSU),
N. J. Klingler (GSFC/UMBC/CRESSTII), K. L. Page (U Leicester),
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 16:43:59 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 231205B (trigger=1200812).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 54.154, +27.146 which is 
   RA(J2000) = 03h 36m 37s
   Dec(J2000) = +27d 08' 47"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single peak
structure with a duration of about 40 sec.  However there
may be activity before the start of the immediately-available
data, as the burst occurred during a pre-planned slew.  The peak count
rate was ~6000 counts/sec (15-350 keV), at T-3, before the
nominal trigger time. 

The XRT began observing the field at 16:47:54.0 UT, 234.5 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 54.14912, 27.14099 which is equivalent
to:
   RA(J2000)  = 03h 36m 35.79s
   Dec(J2000) = +27d 08' 27.6"
with an uncertainty of 3.5 arcseconds (radius, 90% containment). This
location is 23 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 starting 237 seconds after the
BAT trigger. No credible afterglow candidate has been found in
the initial data products. 

Burst Advocate for this burst is P. A. Evans (pae9 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/)