GCN Circular 11991

M. Stamatikos (OSU/NASA/GSFC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
D. N. Burrows (PSU), V. D'Elia (ASDC), N. Gehrels (NASA/GSFC),
J. M. Gelbord (PSU), S. T. Holland (CRESST/USRA/GSFC),
J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA),
N. P. M. Kuin (UCL-MSSL), O. M. Littlejohns (U Leicester),
V. Mangano (INAF-IASFPA), C. B. Markwardt (NASA/GSFC),
F. E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB),
P. T. O\'Brien (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL), P. Romano (INAF-IASFPA), M. H. Siegel (PSU),
R. L. C. Starling (U Leicester), C. A. Swenson (PSU),
E. Troja (NASA/GSFC/ORAU) and T. N. Ukwatta (MSU) report on behalf of
the Swift Team:

At 17:35:45 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 110503A (trigger=452685).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 132.800, +52.216 which is 
   RA(J2000)  =  08h 51m 12s
   Dec(J2000) = +52d 12' 56"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single structure
with a duration of about 10 sec.  The peak count rate
was ~17,000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 17:37:19.2 UT, 93.6 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 132.7778, +52.2067 which is equivalent to:
   RA(J2000)  = 08h 51m 06.67s
   Dec(J2000) = +52d 12' 24.1"
with an uncertainty of 5.1 arcseconds (radius, 90% containment). This
location is 58 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 nominal 150.000 seconds with the White
filter starting 212 seconds after the BAT trigger. There is a candidate
afterglow in the list of sources generated on-board at
  RA(J2000)  =	08:51:06.24 = 132.77598
  DEC(J2000) = +52:12:27.5  =  52.20764
with a 90%-confidence error radius of about 1.10 arc sec. This position is 5.2
arc sec. from the center of the XRT error circle. The estimated magnitude is
15.75. No correction has been made for the expected extinction corresponding to
E(B-V) of 0.02. 

Burst Advocate for this burst is M. Stamatikos (Michael.Stamatikos-1 AT nasa.gov). 
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.)