[vsnet-grb-info 16620] Swift Trigger 642453: a possible GRB

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17901
SUBJECT: Swift Trigger 642453: a possible GRB
DATE:    15/06/04 03:18:19 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

V. D'Elia (ASDC), S. D. Barthelmy (GSFC), J. R. Cummings (NASA/UMBC),
L. Izzo (URoma/ICRA), J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC)
and M. H. Siegel (PSU) report on behalf of the Swift Team:

At 03:00:10 UT, the Swift Burst Alert Telescope (BAT) triggered and
located a possible GRB (trigger=642453).  Swift slewed immediately to 
the location.  The BAT on-board calculated location is 
RA, Dec 238.343, -46.622 which is 
   RA(J2000) = 15h 53m 22s
   Dec(J2000) = -46d 37' 19"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is usual for an image trigger, there
is no activity visible in the immediately-available lightcurve. 

The XRT began observing the field at 03:02:28.4 UT, 138.1 seconds after
the BAT trigger. No source was detected in 35 s of promptly downlinked
data. We are waiting for the full dataset to detect and localise the
XRT counterpart. 

UVOT took a finding chart exposure of  96 seconds with the White filter
starting 141 seconds after the BAT trigger. No credible 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 19.6 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 the expected extinction corresponding to E(B-V) of
0.95. 

Due to the lack of a rate increase trigger, and the non-detection
of a counterpart in the relatively short XRT observation, we cannot
confirm that this is a real astrophysical source at this time. 
A determination of the reality of this event will require the
full downlinked dataset and possibly further XRT observations. 

Burst Advocate for this burst is V. D'Elia (delia AT asdc.asi.it). 
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.)