GCN Circular 17862
C. Gronwall (PSU), A. Y. Lien (GSFC/UMBC) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 08:49:06 UT, the Swift Burst Alert Telescope (BAT) detected a marginal significance peak in an non-rate-triggered image (trigger=641332). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 353.476, -35.987 which is RA(J2000) = 23h 33m 54s Dec(J2000) = -35d 59' 13" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is usual with an image trigger, the available BAT light curve shows no significant structure. The XRT began observing the field at 08:51:27.7 UT, 141.3 seconds after the BAT trigger. No source was detected in 348 s of promptly downlinked data, which covered 98% 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 150 seconds with the White filter starting 145 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 0.02. Because this is a marginal significance detection of a peak in a non-rate-triggered image, with no corresponding source in the XRT data, we believe that this is noise fluctuation and not an astrophysical source.