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GCN Circular 13913

Subject
GRB 121028A: Swift detection of a burst
Date
2012-10-28T05:31:03Z (12 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
R. L. C. Starling (U Leicester), C. Gronwall (PSU),
H. A. Krimm (CRESST/GSFC/USRA), K. L. Page (U Leicester),
D. M. Palmer (LANL), M. H. Siegel (PSU) and T. N. Ukwatta (MSU) report
on behalf of the Swift Team:

At 05:04:31 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 121028A (trigger=536897).  Swift slewed immediately to the burst.   
The BAT on-board calculated location is
RA, Dec 271.923, -2.285 which is
  RA(J2000) = 18h 07m 42s
  Dec(J2000) = -02d 17' 04"
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 30 sec.  The peak count rate
was ~2500 counts/sec (15-350 keV), at ~1 sec after the trigger.

The XRT began observing the field at 05:06:41.7 UT, 129.8 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 271.8995, -2.2936 which
is equivalent to:
   RA(J2000)  = 18h 07m 35.89s
   Dec(J2000) = -02d 17' 36.8"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 90 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 in excess of the Galactic value (2.48 x
10^21 cm^-2, Kalberla et al. 2005), with an excess column of 4.4
(+4.35/-3.23) x 10^21 cm^-2 (90% confidence).

UVOT took a finding chart exposure of 150  seconds with the White filter starting
134 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 19.2 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 18.0 mag. No
correction has been made for extinction.

Due to the maintenance work at Goddard this weekend (GCN 13905) there
may be a delay in receiving the full dataset, and thus refined
analyses may not be available until late Sunday/early Monday.

Burst Advocate for this burst is R. L. C. Starling (rlcs1 AT star.le.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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