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/)