GCN Circular 17919

N. Gehrels (NASA/GSFC), J. A. Kennea (PSU), D. M. Palmer (LANL) and
B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team:

At 11:41:14 UT, the Swift Burst Alert Telescope (BAT) triggered and
located a bright source, probably H1743-322, which is currently in 
outburst (Atel #7607; Zhang et al.).  Due to a known race condition
in the Swift BAT software, this was misidentified as a different location
which corresponds to a different source. 

Since the misidentified source has a low catalog threshold, it was
considered unusually bright, triggering a 'Transient Source' response. 
This included GCN Notices and a Swift follow-up repoint. 

The XRT began observing the field at 12:00:15.4 UT, 1141.1 seconds
after the BAT trigger. No source was detected in 997 s of promptly
downlinked data. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 1144 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. 

Because of the software race condition, H1743-322 was not in
the XRT FOV after Swift slewed to the incorrect location. 
Preplanned observations of H1743-322 have already been 
made and more are scheduled.