GCN Circular 13602

F. E. Marshall (NASA/GSFC), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), B.P. Gompertz (U Leicester),
C. Guidorzi (U Ferrara), J. A. Kennea (PSU),
O. M. Littlejohns (U Leicester), C. B. Markwardt (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL) and
E. Troja (NASA/GSFC/ORAU) report on behalf of the Swift Team:

At 07:09:37 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120807A (trigger=530267).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 241.211, -47.490 which is 
   RA(J2000) = 16h 04m 51s
   Dec(J2000) = -47d 29' 23"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single peak 
structure with a duration of about 15 sec.  The peak count rate
was ~2000 counts/sec (15-350 keV), at ~2 sec after the trigger. 

The XRT began observing the field at 07:10:49.4 UT, 71.6 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 241.2594,
-47.4797 which is equivalent to:
   RA(J2000)  = 16h 05m 02.26s
   Dec(J2000) = -47d 28' 47.0"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 123 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 in excess of the Galactic value (4.94 x
10^21 cm^-2, Kalberla et al. 2005), with an excess column of 3.5
(+4.80/-2.19) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 75 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers none of
the XRT error circle. The 8'x8' region for the list of sources generated
on-board covers 100% of the XRT error circle. The list of sources is typically
complete to about 18 mag. No correction has been made for the large, but
uncertain extinction expected. 

Burst Advocate for this burst is F. E. Marshall (marshall 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.)