TITLE:   GCN CIRCULAR
NUMBER:  6728
SUBJECT: GRB 070809: Swift detection of a short burst
DATE:    07/08/09 19:48:41 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

F. E. Marshall (NASA/GSFC), D. N. Burrows (PSU), M. M. Chester (PSU),
J. R. Cummings (NASA/UMBC), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), C. Guidorzi (Univ Bicocca&INAF-OAB),
S. T. Holland (CRESST/GSFC/USRA), J. A. Kennea (PSU),
K. L. Page (U Leicester), D. M. Palmer (LANL),
P. Romano (Univ. Bicocca & INAF-OAB), T. Sakamoto (NASA/ORAU),
G. Sato (GSFC/ISAS), B. Sbarufatti (INAF-IASFPA),
M. Stamatikos (NASA/ORAU) and R. L. C. Starling (U Leicester) report
on behalf of the Swift Team:

At 19:22:17 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070809 (trigger=287344).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 203.782, -22.134 which is 
   RA(J2000) = 13h 35m 08s
   Dec(J2000) = -22d 08' 01"
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 2 sec.  The peak count rate
was ~2500 counts/sec (15-350 keV), at ~0 sec after the trigger. 
It is currently unclear from the spectral data if this is a short 
hard burst. 

The XRT began observing the field at 19:23:28 UT, 71 seconds after the
BAT trigger. Using prompt downlinked data, we found a fading X-ray source
located at RA, Dec 203.7708, -22.1408 which is equivalent to
   RA(J2000)  =  13h 35m 04.99s
   Dec(J2000) = -22d 08' 26.2"
with an uncertainty of 4.0 arcseconds (radius, 90% containment). 
This location is 44.7 arcseconds from the BAT on-board position,
inside the BAT error circle. 

UVOT took a finding chart exposure of nominal 400 seconds with the V
filter starting 74 seconds after the BAT trigger. However, the 8'x8'
region for the list of sources generated on-board does not cover the
ground-generated XRT error circle, so no statement can be made
regarding an optical counterpart. 

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.)