GCN Circular 8330

W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (NASA/UMBC),
P. A. Evans (U Leicester), S. D. Hunsberger (PSU),
C. B. Markwardt (CRESST/GSFC/UMD), K. L. Page (U Leicester),
D. M. Palmer (LANL), A. M. Parsons (GSFC), M. Stamatikos (NASA/ORAU),
R. L. C. Starling (U Leicester) and M. C. Stroh (PSU) report on behalf
of the Swift Team:

At 05:23:52 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 081007 (trigger=330856).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 339.976, -40.136 which is 
   RA(J2000) = 22h 39m 54s
   Dec(J2000) = -40d 08' 08"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a duration of about 25 sec.  The peak count rate
was 1500 counts/sec (15-350 keV), at 1 sec after the trigger. 

The XRT began observing the field at 05:25:32.1 UT, 99.3 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 339.96077, -40.14675 which
is equivalent to:
   RA(J2000)  = 22h 39m 50.58s
   Dec(J2000) = -40d 08' 48.3"
with an uncertainty of 3.1 arcseconds (radius, 90% containment). This
location is 57 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
1.38e+20 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 1.53e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 108 seconds after the BAT trigger. There is a candidate
afterglow in the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	22:39:50.40 = 339.9600
  DEC(J2000) = -40:08:48.8  = -40.1469
with a 1-sigma error radius of about 0.5 arc sec. This position is 2.2 arc sec. 
from the center of the XRT error circle. The estimated magnitude is 17.0 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 0.01. 

Burst Advocate for this burst is W. H. Baumgartner (wayne 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.)