TITLE:   GCN CIRCULAR
NUMBER:  15533
SUBJECT: GRB 131128A: Swift detection of a burst
DATE:    13/11/28 15:22:39 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

E. Sonbas (NASA/GSFC/Adiyaman Univ.), W. H. Baumgartner (GSFC/UMBC),
M. G. Bernardini (INAF-OAB), S. B. Cenko (GSFC),
P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), S. T. Holland (STScI),
A. Y. Lien (NASA/GSFC/ORAU), D. Malesani (DARK/NBI),
C. B. Markwardt (NASA/GSFC), F. E. Marshall (NASA/GSFC),
A. Maselli (INAF-IASFPA), A. Melandri (INAF-OAB),
P. T. O'Brien (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL), M. H. Siegel (PSU),
R. L. C. Starling (U Leicester) and E. Troja (NASA/GSFC/UMCP) report
on behalf of the Swift Team:

At 15:06:24 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 131128A (trigger=579683).  Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 355.323, +31.279 which is
   RA(J2000) = 23h 41m 18s
   Dec(J2000) = +31d 16' 45"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty).  The BAT light curve showed a single FRED peak
structure with a duration of about 3 sec with a possible precursor
around T-8.  The peak count rate was ~3000 counts/sec (15-350 keV),
at ~0 sec after the trigger.

The XRT began observing the field at 15:07:51.3 UT, 86.8 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 355.3084,
31.3057 which is equivalent to:
   RA(J2000)  = 23h 41m 14.02s
   Dec(J2000) = +31d 18' 20.7"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). This
location is 106 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 5.16
x 10^20 cm^-2 (Kalberla et al. 2005).

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 90 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 none of
the XRT error circle. 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 0.07.

Burst Advocate for this burst is E. Sonbas (edasonbas AT yahoo.com).
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.)