[vsnet-grb-info 16072] Swift Trigger 628458 likely not astrophysical

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17354
SUBJECT: Swift Trigger 628458 likely not astrophysical
DATE:    15/01/27 11:52:19 GMT
FROM:    Jamie A. Kennea at PSU/Swift-XRT  <kennea at swift.psu.edu>

P. D'Avanzo (INAF-OAB), P. A. Evans (U Leicester), J. A. Kennea (PSU)
and A. Y. Lien (GSFC/UMBC) report on behalf of the Swift Team:

At 11:25:54 UT, the Swift Burst Alert Telescope (BAT) triggered (trigger=628458). 
Swift slewed immediately to the burst.  This was a sub-threshold image trigger 
spatially coincident with the galaxy NGC 4570. 
The BAT on-board calculated location is 
RA, Dec 189.211, +7.330 which is 
   RA(J2000) = 12h 36m 51s
   Dec(J2000) = +07d 19' 47"
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 11:37:57.7 UT, 722.9 seconds after
the BAT trigger. No source was detected in 606 s of promptly downlinked
data, which covered 90% of the BAT error circle. We are waiting for the
full dataset to detect and localise the XRT counterpart. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 726 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
0.02.