[vsnet-grb-info 7011] GRB 081203: Swift detection of a burst with a bright optical counterpart

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8595
SUBJECT: GRB 081203: Swift detection of a burst with a bright optical counterpart
DATE:    08/12/03 14:09:33 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at lheamail.gsfc.nasa.gov>

A. M. Parsons (GSFC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU),
P.A. Curran (MSSL-UCL), P. A. Evans (U Leicester),
O. Godet (U Leicester), C. Gronwall (PSU),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
V. La Parola (INAF-IASFPA), V. Mangano (INAF-IASFPA),
J. Mao (INAF-OAB), R. Margutti (Univ Bicocca&OAB),
F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester),
J. P. Osborne (U Leicester), C. Pagani (PSU),
K. L. Page (U Leicester), B. Preger (ASDC), P. Romano (INAF-IASFPA),
B. Sbarufatti (INAF-IASFPA), R. L. C. Starling (U Leicester),
E. Troja (INAF-IASFPA), T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU)
report on behalf of the Swift Team:

At 13:57:11 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 081203 (trigger=336489).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 233.033, +63.498 which is 
   RA(J2000)  =  15h 32m 08s
   Dec(J2000) = +63d 29' 54"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a two peak
structure with a duration of about 70 sec.  The peak count rate
was ~4000 counts/sec (15-350 keV), at ~32 sec after the trigger. 

The XRT began observing the field at 13:58:34.7 UT, 83.1 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 233.0316, +63.5207 which is equivalent to:
   RA(J2000)  = 15h 32m 07.58s
   Dec(J2000) = +63d 31' 14.5"
with an uncertainty of 5.9 arcseconds (radius, 90% containment). This
location is 81 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 92 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	15:32:07.58 = 233.03158
  DEC(J2000) = +63:31:14.9  = 63.52081
with a 90%-confidence error radius of about 0.74 arc sec. This position is 0.4
arc sec. from the center of the XRT error circle. The estimated magnitude is
14.55 with a 1-sigma error of about 0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.02. 

Burst Advocate for this burst is A. M. Parsons (parsons AT milkyway.gsfc.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.)