GCN Circular 36593

J.D. Gropp (PSU), R. Gupta (NASA/GSFC), A. Y. Lien (U Tampa) and
D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 21:30:20 UT, the Swift Burst Alert Telescope (BAT) triggered on
a rate increase and a marginal peak in the resulting image
(trigger=1232465).  Swift slewed immediately to the peak location. 
The BAT on-board calculated location is 
RA, Dec 108.731, -6.206 which is 
   RA(J2000) = 07h 14m 55s
   Dec(J2000) = -06d 12' 20"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty). The available BAT light curve does not show any
significant fluctuations above the noise level. 

The XRT began observing the field at 21:31:59.9 UT, 99.7 seconds after
the BAT trigger. No source was detected in 559 s of promptly downlinked
data. 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 104 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 large, but uncertain, extinction expected. 

Due to the marginal significance of the initial rate trigger (6.5 sigma
in 0.032 s) and the BAT image (6.8 sigma), and the lack of an observed
counterpart in the XRT and UVOT data, we believe that this is probably
a statistical fluctuation and not a real astrophysical event. 

Further analysis of the complete downlinked dataset will be used
to conclusively rule out this event.