[vsnet-grb-info 10122] Swift Trigger 442539 is probably not a GRB

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  11572
SUBJECT: Swift Trigger 442539 is probably not a GRB
DATE:    11/01/16 12:26:02 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

C. B. Markwardt (NASA/GSFC), A. P. Beardmore (U Leicester),
D. N. Burrows (PSU), J. M. Gelbord (PSU),
S. T. Holland (CRESST/USRA/GSFC), H. A. Krimm (CRESST/GSFC/USRA),
N. P. M. Kuin (UCL-MSSL), O. M. Littlejohns (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL),
P. Romano (INAF-IASFPA), A. Rowlinson (U Leicester),
B. Sbarufatti (INAF-OAB/IASFPA), M. H. Siegel (PSU) and
R. L. C. Starling (U Leicester) report on behalf of the Swift Team:

At 12:04:25 UT, the Swift Burst Alert Telescope (BAT) triggered and
located trigger 442539.  Swift slewed immediately to the location. 
The BAT on-board calculated location is 
RA, Dec 204.936, +55.160 which is 
   RA(J2000) = 13h 39m 45s
   Dec(J2000) = +55d 09' 37"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is usual with an image trigger, we do not
see obvious structure in the BAT light curve with the currently 
available data.  With ground processing, the image significance is only 
6.7 sigma, which is below our normal image significance threshold. 

The XRT began observing the field at 12:06:53.9 UT, 148.5 seconds after
the BAT trigger. No source was detected in the promptly available XRT
data. We are waiting for the full dataset to search for an X-ray counterpart. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 154 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. 

Due to the marginal BAT detection of the event (7.4 sigma in the
on-board image, 6.7 sigma in ground-based analysis) and the lack
of detection by XRT and UVOT, we believe that this is probably not
a true astrophysical event.  Further determination of its reality
will require the full downlinked data, available in a few hours. 

Burst Advocate for this burst is C. B. Markwardt (Craig.Markwardt AT nasa.gov). 
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.)