GCN Circular 6594

T. Sakamoto (NASA/ORAU), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), M. M. Chester (PSU),
N. Gehrels (NASA/GSFC), O. Godet (U Leicester),
S. T. Holland (CRESST/GSFC/USRA), S. Immler (GSFC/UMCP),
F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester),
D. M. Palmer (LANL), G. Sato (GSFC/ISAS), B. Sbarufatti (INAF-IASFPA)
and R. L. C. Starling (U Leicester) report on behalf of the Swift
Team:

At 20:05:57 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070704 (trigger=283791).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 354.723, +66.248 which is 
   RA(J2000)  =  23h 38m 54s
   Dec(J2000) = +66d 14' 52"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve does not show anything
significant, as is typical for image-trigger events.  There is a possibility
that the burst started at ~T-70 sec, but since Swift was executing
a preplanned slew from ~T-35 to T_0 sec, it is difficult to interpret
the TDRSS lightcurve. 

The XRT began observing the field at 20:08:30 UT, 153 seconds after the
BAT trigger. The on-board XRT position was not correct, because the algorithm 
centroided on a hot pixel. 
From the ground data analysis,  a moderately bright and uncatalogued X-ray 
source was found at RA, Dec 354.69922, + 66.25226 which is
   RA(J2000)  =  23h 38m 47.8s
   Dec(J2000) =  66d 15' 08.1"
with an uncertainty of 5.5 arcseconds (radius, 90% containment). 
This location is 40.8 arcseconds from the BAT on-board position,
outside the BAT error circle. The initial flux in the 2.5s image
was 3.7e-10 erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 158 seconds after the BAT trigger, and a
finding chart exposure of 400 seconds with the V filter starting 265
seconds after the BAT trigger. No afterglow candidate has been found
in the initial data products. The 8'x8' region for the list of
sources generated on-board covers 100% of the BAT and XRT error
circles. The 2.7'x2.7' sub-image does not cover the XRT error circle. 
The list of sources is typically complete to about 18.0 mag. No
correction has been made for the large, but uncertain extinction
expected. 

Burst Advocate for this burst is T. Sakamoto (takanori 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.)