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GCN Circular 13408

GRB 120703A: Swift detection of a bright burst with an optical afterglow
2012-07-03T17:34:05Z (12 years ago)
David Palmer at LANL <>
B.-B. Zhang (PSU), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU),
M. M. Chester (PSU), N. Gehrels (NASA/GSFC), D. Grupe (PSU),
F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL),
J. L. Racusin (NASA/GSFC) and T. N. Ukwatta (MSU) report on behalf of
the Swift Team:

At 17:25:22 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120703A (trigger=525671).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 339.357, -29.736 which is 
   RA(J2000) = 22h 37m 26s
   Dec(J2000) = -29d 44' 08"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multiply-peaked
structure with a duration of about 50 sec.  The peak count rate
was ~14000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 17:26:48.9 UT, 86.7 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 339.35607, -29.72444 which is
equivalent to:
   RA(J2000)  = 22h 37m 25.46s
   Dec(J2000) = -29d 43' 28.0"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 41 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 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (1.21 x
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 3.5
(+1.97/-1.72) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 91 seconds after the BAT trigger. There is a candidate afterglow in
the list of sources generated on-board at
  RA(J2000)  =	22:37:25.71 = 339.35711
  DEC(J2000) = -29:43:23.5  = -29.72320
with a 90%-confidence error radius of about 1.10 arc sec. This position is 5.5
arc sec. from the center of the XRT error circle. The estimated magnitude is
18.51. No correction has been made for the expected extinction corresponding to
E(B-V) of 0.02. 

Burst Advocate for this burst is B.-B. Zhang (bbzhang AT 
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:
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