TITLE:   GCN CIRCULAR
NUMBER:  8462
SUBJECT: GRB 081102: Swift detection of a burst
DATE:    08/11/02 18:10:16 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>

T. N. Ukwatta (GSFC/GWU), S. D. Barthelmy (GSFC),
J. R. Cummings (NASA/UMBC), N. Gehrels (NASA/GSFC),
C. Gronwall (PSU), C. Guidorzi (INAF-OAB),
S. T. Holland (CRESST/USRA/GSFC), W.B Landsman (GSFC),
V. Mangano (INAF-IASFPA), J. Mao (INAF-OAB),
P. T. O'Brien (U Leicester), D. M. Palmer (LANL),
P. Romano (INAF-IASFPA), B. Sbarufatti (INAF-IASFPA),
M. Stamatikos (NASA/ORAU) and H. Ziaeepour (UCL-MSSL) report on
behalf of the Swift Team:

At 17:44:39 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 081102 (trigger=333427).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 331.182, +52.993 which is 
   RA(J2000)  = 22h 04m 44s
   Dec(J2000) = +52d 59' 36"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows multiple peaks
with a duration of about 40 sec.  The peak count rate
was ~1800 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 17:46:11.5 UT, 92.0 seconds after
the BAT trigger. Using promptly downlinked data we find a bright, fading
uncatalogued X-ray source located at RA, Dec 331.17357, 52.99345 which
is equivalent to:
   RA(J2000)  = 22h 04m 41.66s
   Dec(J2000) = +52d 59' 36.4"
with an uncertainty of 3.3 arcseconds (radius, 90% containment). This
location is 18 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
4.95e+21 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 2.85e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White
(160-650 nm) filter starting 99 seconds after the BAT trigger. No
afterglow candidate has  been found in the initial data products. The
2.7'x2.7' sub-image covers all of the XRT error circle.  The image
is typically complete to about 18 mag. No  correction has been made
for the expected extinction corresponding to E(B-V) of  0.81. 

Burst Advocate for this burst is T. N. Ukwatta (tilan.ukwatta AT gmail.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.)