GCN Circular 12215

S. R. Oates (UCL-MSSL), A. P. Beardmore (U Leicester),
S. T. Holland (CRESST/USRA/GSFC), E. A. Hoversten (PSU),
A. Melandri (INAF-OAB), C. J. Mountford (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL), C. J. Saxton (UCL-MSSL)
and T. N. Ukwatta (MSU) report on behalf of the Swift Team:

At 11:09:30 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 110731A (trigger=458448).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 280.521, -28.546 which is 
   RA(J2000) = 18h 42m 05s
   Dec(J2000) = -28d 32' 44"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multiple-peaked
structure with a duration of about 20 sec.  The peak count rate
was ~20000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 11:10:36.9 UT, 66.4 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 280.5042, -28.5363 which is equivalent to:
   RA(J2000)  = 18h 42m 01.00s
   Dec(J2000) = -28d 32' 10.6"
with an uncertainty of 4.8 arcseconds (radius, 90% containment). This
location is 63 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. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 75 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	18:42:01.01 = 280.50419
  DEC(J2000) = -28:32:13.7  = -28.53713
with a 90%-confidence error radius of about 0.61 arc sec. This position is 3.0
arc sec. from the center of the XRT error circle. The estimated magnitude is
15.80 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.17. 

Burst Advocate for this burst is S. R. Oates (sro AT mssl.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.)