[vsnet-grb-info 4977] GRB 070802: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6692
SUBJECT: GRB 070802: Swift detection of a burst
DATE:    07/08/02 07:46:54 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at lheamail.gsfc.nasa.gov>

S. D. Barthelmy (GSFC), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), S. Immler (GSFC/UMCP),
V. Mangano (INAF-IASFPA), C. B. Markwardt (CRESST/GSFC/UMD),
P. T. O'Brien (U Leicester), J. P. Osborne (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL),
P. Romano (Univ. Bicocca & INAF-OAB), G. Sato (GSFC/ISAS),
B. Sbarufatti (INAF-IASFPA), M. Stamatikos (NASA/ORAU),
G. Tagliaferri (INAF-OAB), D. E. Vanden Berk (PSU) and
S. D. Vergani (DIAS-DCU) report on behalf of the Swift Team:

At 07:07:25 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070802 (trigger=286809).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 36.851, -55.536 which is 
   RA(J2000)  =  02h 27m 24s
   Dec(J2000) = -55d 32' 10"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a peak
with a duration of roughly 30 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~6 sec after the trigger. 

The XRT began taking data at 07:09:43 UT, 138 seconds after the BAT
trigger.  The XRT on-board centroid algorithm did not find a source
in the image, however using 510s of promptly available data we find
an uncatalogued source at Ra, Dec=36.8987, -55.2781 degrees, which is
equivalent to:
  RA(J2000) =  02h 27m 35.69s
  Dec(J2000) = -55d 31' 40.1"

with an estimated uncertainty of 4.4 arcsec (radius, 90% containment). 
This source is 101.6 arcsec from the BAT position, within the
BAT error circle. 

UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 141 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 of E(B-V) = 0.026. 

S. Immler is the burst advocate for this burst.  Please contact him
for any questions concerning this burst: immler AT milkyway.gsfc.nasa.gov .