GCN Circular 8217

P. Schady (MSSL-UCL), A. P. Beardmore (U Leicester),
J. R. Cummings (NASA/UMBC), P. A. Evans (U Leicester),
O. Godet (U Leicester), C. Gronwall (PSU),
C. B. Markwardt (CRESST/GSFC/UMD), K. L. Page (U Leicester),
D. M. Palmer (LANL), A. M. Parsons (GSFC), D. Perez (U Leicester),
R. L. C. Starling (U Leicester) and E. Troja (INAF-IASFPA) report on
behalf of the Swift Team:

At 06:46:54 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080913 (trigger=324561).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 65.725, -25.110 which is 
   RA(J2000) = 04h 22m 54s
   Dec(J2000) = -25d 06' 36"
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 10 sec.  The peak count rate
was ~800 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 06:48:33.6 UT, 99.5 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 65.72800,
-25.12945 which is equivalent to:
   RA(J2000)  = 04h 22m 54.72s
   Dec(J2000) = -25d 07' 46.0"
with an uncertainty of 2.4 arcseconds (radius, 90% containment). This
location is 70 arcseconds from the BAT onboard position, within the BAT
error circle. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of
3.17e+20 cm^-2 (Kalberla et al. 2005). 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm)  filter starting 105 seconds after the BAT trigger. No
afterglow candidate has  been found in the initial data products. The
2.7'x2.7' sub-image covers 25% of  the BAT error circle and 100% of
the XRT error circle. The 3-sigma upper limit at the XRT position is
20.7 mag.  The 8'x8' region for the list of sources generated
on-board covers 100% of the  BAT error circle. The list of sources is
typically complete to about 18 mag. No  correction has been made for
the expected extinction corresponding to E(B-V) of  0.04. 

Burst Advocate for this burst is P. Schady (ps AT mssl.ucl.ac.uk). 
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.)