GCN Circular 6743

F. E. Marshall (NASA/GSFC), P. J. Brown (PSU),
J. R. Cummings (NASA/UMBC), N. Gehrels (NASA/GSFC),
O. Godet (U Leicester), C. Guidorzi (Univ Bicocca&INAF-OAB),
S. T. Holland (CRESST/GSFC/USRA), J. A. Kennea (PSU),
V. Mangano (INAF-IASFPA), C. B. Markwardt (CRESST/GSFC/UMD),
J. P. Osborne (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL), B. Sbarufatti (INAF-IASFPA),
M. Stamatikos (NASA/ORAU), R. L. C. Starling (U Leicester),
E. Troja (INAF-IASFPA), T. N. Ukwatta (GSFC/GWU) and
D. E. Vanden Berk (PSU) report on behalf of the Swift Team:

At 15:19:17 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070810B (trigger=287409).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 8.940, +8.835 which is 
   RA(J2000) = 00h 35m 46s
   Dec(J2000) = +08d 50' 07"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single short spike
with a duration of < 0.2 sec.  The peak count rate
was ~4500 counts/sec (15-350 keV), at ~0 sec after the trigger.  The
lightcurves in different bands indicate an intermediate spectrum that is 
neither hard nor soft. 

The XRT began taking data at 15:20:19 UT, 62 seconds after the BAT
trigger.  The XRT on-board centroid algorithm did not find a source in the
image and we do not detect a source in the initial SPER images. However, it is
possible that the source is very faint or lies outside the SPER window. 
We await down-linked data to detect and determine a position 
for the source. 

UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 65 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. The typical 3-sigma upper limit has been about 18.5 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 extinction corresponding to the expected
reddening of E(B-V)=0.05. 

We note the presence of the bright extended galaxy 
2MASX J00355339+0849273 (= LEDA 1354367) within the BAT error circle. 

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.)