GCN Circular 13843
S. D. Barthelmy (GSFC), N. Gehrels (NASA/GSFC), J. A. Kennea (PSU), C. B. Markwardt (NASA/GSFC) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 23:57:42 UT, the Swift Burst Alert Telescope (BAT) triggered and located trigger 535733. Swift slewed immediately to the location. The BAT on-board calculated location is RA, Dec 277.193, -10.479 which is RA(J2000) = 18h 28m 46s Dec(J2000) = -10d 28' 42" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As typical for image triggers (64-sec), the prompt lightcurve data shows nothing significant. This position is marginally consistent with the known source SAX J1828.5-1037. We note that the detection significance is marginal as well. The XRT began observing the field at 23:59:42.7 UT, 120.5 seconds after the BAT trigger. No source was detected in the 2.5-s promptly available image. We are waiting for the full dataset to detect and localise the XRT counterpart. UVOT took a finding chart exposure of 6 seconds with the White filter starting 123 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. Results from the list of sources generated on-board are not available at this time. No correction has been made for the large, but uncertain extinction expected.