[vsnet-grb-info 4599] GRB 070429B: Swift detection of a short burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6358
SUBJECT: GRB 070429B: Swift detection of a short burst
DATE:    07/04/29 03:41:59 GMT
FROM:    Craig Markwardt at NASA/GSFC/UMD  <craigm at milkyway.gsfc.nasa.gov>

C. B. Markwardt (GSFC/UMD), L. M. Barbier (NASA/GSFC),
S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester),
J. K. Cannizzo (NASA/UMBC), M. M. Chester (PSU),
N. Gehrels (NASA/GSFC), S. D. Hunsberger (PSU),
W. B. Landsman (NASA/GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL), G. Sato (GSFC/ISAS) and
R. L. C. Starling (U Leicester) report on behalf of the Swift Team:

At 03:09:04 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070429B (trigger=277582).  Swift slewed to the burst
following a 165 second delay due to the Earth-limb constraint. 
The BAT on-board calculated location is 
RA, Dec 328.024, -38.844 which is 
   RA(J2000)  =  21h 52m 06s
   Dec(J2000) = -38d 50' 37"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a short spike
with a duration of about 700 msec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

No source was automatically found onboard by the XRT; however, 213s of
downlinked data suggest there is a possible source at RA, DEC
(degrees) = 328.01551, -38.82670 which is   
RA(J2000) = 21h 52m 03.7s
Dec(J2000)= -38d 49' 36.1"  
with an uncertainty of 9.1 arcsec (90% containment). 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 247 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, and fully
covers the possible XRT position. 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 reddening of E(B-V)=0.026.