TITLE:   GCN CIRCULAR
NUMBER:  12885
SUBJECT: GRB 120121A: Swift detection of a burst
DATE:    12/01/21 10:00:46 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

K. L. Page (U Leicester), A. P. Beardmore (U Leicester),
P. A. Evans (U Leicester), J. A. Kennea (PSU), D. M. Palmer (LANL),
M. H. Siegel (PSU), R. L. C. Starling (U Leicester) and
B.-B. Zhang (PSU) report on behalf of the Swift Team:

At 09:42:19 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120121A (trigger=512164).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 249.336, -23.954 which is 
   RA(J2000) = 16h 37m 21s
   Dec(J2000) = -23d 57' 14"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peaked
FRED structure with a duration of about 40 sec.  The peak count rate
was ~800 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 09:44:18.7 UT, 119.4 seconds after
the BAT trigger. No source was detected in the 2.5-s promptly available
image. We are waiting for the full dataset to detect and localise the
XRT counterpart. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 123 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 25% of
the BAT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 
The 8'x8' region for the list of sources generated on-board covers 100% of the
BAT 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
0.84. 

Burst Advocate for this burst is K. L. Page (kpa AT star.le.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/too.html.)