GCN Circular 6733

J. R. Cummings (NASA/UMBC), S. D. Barthelmy (GSFC),
M. M. Chester (PSU), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/GSFC/USRA), J. A. Kennea (PSU),
C. B. Markwardt (CRESST/GSFC/UMD), D. M. Palmer (LANL) and
M. Stamatikos (NASA/ORAU) report on behalf of the Swift Team:

At 02:11:52 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070810 (trigger=287364).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 189.939, +10.744 which is 
   RA(J2000)  =  12h 39m 45s
   Dec(J2000) = +10d 44' 40"
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 20 sec.  The peak count rate
was ~2500 counts/sec (15-350 keV), at T+0 sec after the trigger. 

The XRT began taking data at 02:13:20 UT, 88 seconds after the BAT
trigger.  The XRT on-board centroid algorithm did not find a source in the
image. Using prompt downlinked data, we find a fading, X-ray source
located at RA, Dec 189.9629, 10.7513  which is
   RA(J2000)  =  12 39 51.10
   Dec(J2000) = +10 45 04.7
with an uncertainty of 3.9 arcsec (radius, 90% containment). This position
is 89 arcminutes from the BAT position. 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 92 seconds after the BAT trigger, and a
finding chart exposure of a nominal 400 seconds starting 198 seconds. 
A possible candidate has been identified visually in the initial data
products, but processing is still underway so no position or
significance is available at this time. The 2.7' x 2.7' sub-image
does not cover the XRT error circle; the 8' x 8' list of sources
covers 100% of the XRT error circle.  The typical 3-sigma upper limit
has been about 18.5 mag. 

No BAT_Position Notice was distributed, because none was received
from the TDRSS system.  This burst occurred during a 24-sec gap
in TDRSS coverage due to a hand-off from one TDRSS satellite to
the next satellite, so none of the initial notices were available
(BAT_Position, FOM, and SC_Slew). 

Burst Advocate for this burst is J. R. Cummings (jayc 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.)