[vsnet-grb-info 15781] Swift Trigger 618673: probable noise event

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17069
SUBJECT: Swift Trigger 618673: probable noise event
DATE:    14/11/15 09:40:13 GMT
FROM:    Caryl Gronwall at PSU/Swift-UVOT  <caryl at swift.psu.edu>

W. H. Baumgartner (GSFC/UMBC), M. De Pasquale (INAF-IASFPA),
C. Gronwall (PSU), A. Maselli (INAF-IASFPA) and
E. Sonbas (NASA/GSFC/Adiyaman Univ.) report on behalf of the Swift
Team:

At 09:10:35 UT, the Swift Burst Alert Telescope (BAT) triggered and
located on trigger 618673.  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 233.024, +32.694 which is 
   RA(J2000) = 15h 32m 06s
   Dec(J2000) = +32d 41' 38"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed nothing of note for this 
low significance image trigger. 

The XRT began observing the field at 09:13:05.1 UT, 149.9 seconds after
the BAT trigger. No source was detected in 859 s of promptly downlinked
data, which covered 97% 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 153 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. 

We believe this trigger to not be from an astrophysical source because
of the low significance of the BAT source in the image domain and the 
lack of an XRT counterpart.