TITLE:   GCN CIRCULAR
NUMBER:  13454
SUBJECT: GRB 120712A: Swift detection of a burst with optical afterglow
DATE:    12/07/12 13:52:34 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>

M. J. Page (UCL-MSSL), A. A. Breeveld (UCL-MSSL), D. N. Burrows (PSU),
V. D'Elia (ASDC), P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
N. P. M. Kuin (UCL-MSSL), O. M. Littlejohns (U Leicester),
F. E. Marshall (NASA/GSFC), S. R. Oates (UCL-MSSL),
K. L. Page (U Leicester), D. M. Palmer (LANL) and
V. N. Yershov (UCL-MSSL) report on behalf of the Swift Team:

At 13:42:27 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120712A (trigger=526351).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 169.605, -20.061 which is 
   RA(J2000)  =  11h 18m 25s
   Dec(J2000) = -20d 03' 38"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a couple of overlapping
peaks with a total duration of about 25 sec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~8 sec after the trigger. 

The XRT began observing the field at 13:43:58.2 UT, 90.9 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 169.59034, -20.03336 which is
equivalent to:
   RA(J2000)  = 11h 18m 21.68s
   Dec(J2000) = -20d 02' 00.1"
with an uncertainty of 4.1 arcseconds (radius, 90% containment). This
location is 111 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 in excess of the Galactic value (3.60 x
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 3
(+2.23/-1.94) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 95 seconds after the BAT trigger. There is a candidate afterglow in
the list of sources generated on-board at
  RA(J2000)  =	11:18:21.23 = 169.58847
  DEC(J2000) = -20:02:01.8  = -20.03383
with a 90%-confidence error radius of about 1.10 arc sec. This position is 6.5
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.10. No correction has been made for the expected extinction corresponding to
E(B-V) of 0.04. 

Burst Advocate for this burst is M. J. Page (mjp AT mssl.ucl.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.)