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GCN Circular 15616

Subject
GRB 131227A: Swift detection of a burst
Date
2013-12-27T05:09:45Z (10 years ago)
From
Mike Siegel at PSU/Swift MOC <siegel@swift.psu.edu>
S. R. Oates (UCL-MSSL), H. A. Krimm (CRESST/GSFC/USRA),
N. P. M. Kuin (UCL-MSSL) and M. H. Siegel (PSU) report on behalf of
the Swift Team:

At 04:44:51 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 131227A (trigger=582184).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 67.386, +28.864 which is 
   RA(J2000) = 04h 29m 33s
   Dec(J2000) = +28d 51' 52"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 20 sec.  The peak count rate
was ~2000 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 04:45:48.0 UT, 57 seconds
after the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source with an enhanced position: RA, Dec 67.3781,
28.8827 which is equivalent to:
   RA(J2000)  = 04h 29m 30.74s
   Dec(J2000) = +28d 52' 57.9"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). 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 in excess of the Galactic value (1.53 x
10^21 cm^-2, Kalberla et al. 2005), with an excess column of 2.1
(+2.23/-1.94) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 6.01e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 66 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
1.02. 

Burst Advocate for this burst is S. R. Oates (samantha.oates AT 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.)
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