[vsnet-grb-info 16705] Swift Trigger 647642 is probably not an astrophysical source

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17986
SUBJECT: Swift Trigger 647642 is probably not an astrophysical source
DATE:    15/07/02 07:19:32 GMT
FROM:    Kim Page at U.of Leicester  <klp5 at leicester.ac.uk>

P. A. Evans (U Leicester), A. Y. Lien (GSFC/UMBC) and
K. L. Page (U Leicester) report on behalf of the Swift Team:

At 06:59:05 UT, the Swift Burst Alert Telescope (BAT) triggered on a
marginal significance peak in an non-rate-triggered image 
(trigger=647642). Swift slewed immediately to the event. 
The BAT on-board calculated location is 
RA, Dec 161.248, +55.989 which is 
   RA(J2000) = 10h 45m 00s
   Dec(J2000) = +55d 59' 22"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty). As is usual with an image trigger, 
the available BAT light curve shows no significant structure. 

The XRT began observing the field at 07:01:44.1 UT, 158.9 seconds after
the BAT trigger. No source was detected in 822 s of promptly downlinked
data. 

UVOT took a finding chart exposure of 145 seconds with the White filter
starting 163 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
0.01. 

Because this is a marginal significance detection of a peak in a 
non-rate-triggered image, with no corresponding source in the XRT 
data, we believe that this is noise fluctuation and not an 
astrophysical source.