[vsnet-grb-info 6580] GRB 080906: Swift detection of a burst with optical afterglow

[GCN Circulars]

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 at 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. 




Burst Advocate for this burst is L. Vetere (vetere AT astro.psu.edu). 
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.)