[vsnet-grb-info 19521] Swift trigger 758168 is probably not an astrophysical source

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21261
SUBJECT: Swift trigger 758168 is probably not an astrophysical source
DATE:    17/06/22 10:51:54 GMT
FROM:    Kim Page at U.of Leicester  <klp5 at leicester.ac.uk>

S. W. K Emery (UCL-MSSL), P. A. Evans (U Leicester),
A. Y. Lien (GSFC/UMBC), K. L. Page (U Leicester) and
B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team:

At 10:32:44 UT, the Swift Burst Alert Telescope (BAT) triggered on noise
near NGC5949 (trigger=758168).  Swift slewed immediately to the location. 
The BAT on-board calculated location is 
RA, Dec 232.221, +64.871 which is 
   RA(J2000) = 15h 28m 53s
   Dec(J2000) = +64d 52' 14"
with an uncertainty of 4 arcmin (radius, 90% containment, including 
systematic uncertainty). As is typical for image triggers, 
there is nothing in the real-time light curve. 

The XRT began observing the field at 10:39:26.2 UT, 401.6 seconds after
the BAT trigger. No source was detected in 391 s of promptly downlinked
data. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 404 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
0.03. 

Given that this is a low significance detection in BAT (5.9 sigma) and that there is
no XRT source, we think this is a non-astrophysical fluctuation in the BAT image
that happens to be close the NGC5949 source.