GCN Circular 31815

A. D'Ai (INAF-IASFPA), S. Dichiara (PSU), S. Laha (GSFC/UMBC),
T. M. Parsotan (GSFC/UMBC/CRESSTII), M. H. Siegel (PSU) and
A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 03:54:42 UT, the Swift Burst Alert Telescope (BAT)  triggered and
located a marginal peak (trigger=1100848). Swift slewed immediately. 
The BAT on-board calculated location is 
RA, Dec 30.692, -61.376 which is 
   RA(J2000) = 02h 02m 46s
   Dec(J2000) = -61d 22' 34"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty). 

The XRT began observing the field at 03:56:24.6 UT, 102.1 seconds after
the BAT trigger. No source was detected in 689 s of promptly downlinked
data, which covered 93% 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 250 seconds with the U filter starting
318 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 16% of the
BAT error circle. The typical 3-sigma upper limit has been about 19.2 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 18.0 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.035. 

Due to the low BAT significance and lack of detection in XRT, we believe that this trigger is not likely an astrophysical event.