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GCN Circular 12720

GRB 111225A: Swift detection of a burst with an optical counterpart
2011-12-25T04:12:26Z (12 years ago)
David Palmer at LANL <>
M. H. Siegel (PSU), W. H. Baumgartner (GSFC/UMBC),
M. M. Chester (PSU), N. Gehrels (NASA/GSFC), D. Grupe (PSU),
F. E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB),
D. M. Palmer (LANL), T. Sakamoto (NASA/UMBC), C. A. Swenson (PSU),
T. N. Ukwatta (MSU) and B.-B. Zhang (PSU) report on behalf of the
Swift Team:

At 03:50:37 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 111225A (trigger=510341).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 13.102, +51.589 which is 
   RA(J2000) = 00h 52m 24s
   Dec(J2000) = +51d 35' 19"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The immediately available lightcurve was
truncated for contact with the ground station. The BAT lightcurve showed 
a rise at around T-10 seconds with flux continuing at least until
T+8 seconds, the limit of of the immediately available data.  
The peak count rate was ~1300 counts/sec (15-350 keV), at ~-2 sec 
after the trigger. 

The XRT began observing the field at 03:52:05.9 UT, 88.1 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 13.1548, 51.5741 which is equivalent to:
   RA(J2000)  = +00h 52m 37.15s
   Dec(J2000) = +51d 34' 26.8"
with an uncertainty of 5.0 arcseconds (radius, 90% containment). This
location is 129 arcseconds from the BAT onboard position, within the
BAT error circle. No event data are yet available to determine the
column density using X-ray spectroscopy. 

The initial flux in the 2.5 s image was 2.96e-09 erg cm^-2 s^-1 (0.2-10

UVOT took a finding chart exposure of 250 seconds with the U filter starting 95
seconds after the BAT trigger. There is a candidate afterglow in the rapidly
available 2.7'x2.7' sub-image at
  RA(J2000)  =	00:52:37.21 =  13.15503
  DEC(J2000) = +51:34:19.5  =  51.57207
with a 90%-confidence error radius of about 0.75 arc sec. This position is 7.3
arc sec. from the center of the XRT error circle. The estimated magnitude is
19.42 with a 1-sigma error of about  0.20. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.26. 

Burst Advocate for this burst is M. H. Siegel (siegel 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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