TITLE:   GCN CIRCULAR
NUMBER:  8186
SUBJECT: GRB 080906: Swift detection of a burst with optical afterglow
DATE:    08/09/06 13:52:03 GMT
FROM:    David Burrows at PSU/Swift  <dxb15@psu.edu>

L. Vetere (PSU), S. D. Barthelmy (GSFC), P. J. Brown (PSU),
D. N. Burrows (PSU), M. M. Chester (PSU), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/USRA/GSFC), H. A. Krimm (CRESST/GSFC/USRA),
J. Mao (INAF-OAB), C. B. Markwardt (CRESST/GSFC/UMD),
F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester),
D. M. Palmer (LANL), J. L. Racusin (PSU),
B. Sbarufatti (INAF-IASFPA), M. Stamatikos (NASA/ORAU),
G. Tagliaferri (INAF-OAB), E. Troja (INAF-IASFPA) and
T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:

At 13:33:16 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080906 (trigger=323984).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 227.890, -80.486 which is 
   RA(J2000) = 15h 11m 34s
   Dec(J2000) = -80d 29' 09"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed one major peak
of duration ~50 sec, with possible smaller peaks.  The peak count rate
was ~2000 counts/sec (15-350 keV), at ~10 sec after the trigger. 

The XRT began observing the field at 13:34:27.6 UT, 71.3 seconds after
the BAT trigger. XRT found a bright, fading, uncatalogued X-ray source located
at RA, Dec 228.0514, -80.5183 which is equivalent to:
   RA(J2000)  = 15h 12m 12.3s
   Dec(J2000) = -80d 31' 05.8"
with an uncertainty of 4.7 arcseconds (radius, 90% containment). This
location is 150 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 100 seconds with the White (160-650 nm)
filter starting 82 seconds after the BAT trigger. There is a candidate
afterglow in the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =  15:12:10.63 = 228.0443
  DEC(J2000) = -80:31:04.1  = -80.5178
with a 1-sigma error radius of about 0.5 arc sec. This position is 4.6 arc sec. 
from the center of the XRT error circle. The estimated magnitude is 19.7 with a
1-sigma error of about 0.5 mag. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.30.