TITLE:   GCN CIRCULAR
NUMBER:  14115
SUBJECT: GRB 121229A: Swift detection of a burst
DATE:    12/12/29 05:15:29 GMT
FROM:    Mike Siegel at PSU/Swift MOC  <siegel@swift.psu.edu>

E. Sonbas (NASA/GSFC/Adiyaman Univ.), V. D'Elia (ASDC),
J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), T. Sakamoto (AGU)
and M. H. Siegel (PSU) report on behalf of the Swift Team:

At 05:00:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 121229A (trigger=544347).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 190.100, -50.594 which is 
  RA(J2000) = 12h 40m 24s
  Dec(J2000) = -50d 35' 37"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  Since this is an image trigger, the BAT light 
curve does not show any particular structure.  The peak count rate 
was ~1000 counts/sec (15-350 keV), at ~5 sec after the trigger. 

The XRT began observing the field at 05:02:47.8 UT, 145.9 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 190.09755, -50.59366 which
is equivalent to:
  RA(J2000)  = 12h 40m 23.41s
  Dec(J2000) = -50d 35' 37.2"
with an uncertainty of 4.1 arcseconds (radius, 90% containment). This
location is 5.7 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
http://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 consistent with the Galactic value of 1.35
x 10^21 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 1.21e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 155 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 100% of
the XRT 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
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
0.16. 

Burst Advocate for this burst is E. Sonbas (edasonbas AT yahoo.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/too.html.)