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GCN Circular 8554

Subject
GRB 081126: Swift detection of a burst
Date
2008-11-26T21:58:18Z (16 years ago)
From
Jamie A. Kennea at PSU/Swift-XRT <kennea@astro.psu.edu>
R. Margutti (Univ Bicocca&OAB), A. P. Beardmore (U Leicester),
P. J. Brown (PSU), D. N. Burrows (PSU), N. Gehrels (NASA/GSFC),
C. Guidorzi (INAF-OAB), S. T. Holland (CRESST/USRA/GSFC),
J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA),
J. Mao (INAF-OAB), F. E. Marshall (NASA/GSFC), C. Pagani (PSU),
P. Romano (INAF-IASFPA), M. Stamatikos (NASA/ORAU),
T. N. Ukwatta (GSFC/GWU), L. Vetere (PSU) and H. Ziaeepour (UCL-MSSL)
report on behalf of the Swift Team:

At 21:34:10 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 081126 (trigger=335647).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 323.542, +48.709 which is 
   RA(J2000) = 21h 34m 10s
   Dec(J2000) = +48d 42' 33"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a total duration of about 40 sec.  The two peaks are about
30 seconds apart. The peak count rate was ~7000 counts/sec (15-350 keV), 
at ~2 sec after the trigger. 

The XRT began observing the field at 21:35:16.0 UT, 65.7 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source with an enhanced position: RA, Dec 323.5150,
48.7097 which is equivalent to:
   RA(J2000)  = 21h 34m 3.60s
   Dec(J2000) = +48d 42' 34.9"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 64 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of
4.13e+21 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 7.07e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White   
filter  starting 75 seconds after the BAT trigger. No credible   
afterglow candidate has  been found in the initial data products. The
 2.7' x 2.7' sub-image covers 100% of  the XRT error circle. The   
estimated 3-sigma limiting magnitude is white > 21 mag.  No 
correction has   been made for the large, but uncertain extinction 
expected.  There is   a high proper motion 2MASS source inside the 
XRT error circle. 

Burst Advocate for this burst is R. Margutti (raffaella.margutti AT brera.inaf.it). 
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.)
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