TITLE: GCN CIRCULAR NUMBER: 19002 SUBJECT: Swift Trigger 672897 is probably not an astrophysical event DATE: 16/02/08 00:19:49 GMT FROM: David Palmer at LANL A. D'Ai (INAF-IASFPA), J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC), A. Maselli (INAF-IASFPA), D. M. Palmer (LANL) and B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team: At 23:49:52 UT, the Swift Burst Alert Telescope (BAT) found a marginal significance fluctuation in an untriggered image (trigger=672897). Swift slewed immediately to the location. The BAT on-board calculated location is RA, Dec 156.059, +19.770 which is RA(J2000) = 10h 24m 14s Dec(J2000) = +19d 46' 14" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is usual for an image trigger, there is no obvious variation in the immediately-available BAT lightcurve. The XRT began observing the field at 23:52:49.7 UT, 177.5 seconds after the BAT trigger. No source was detected in 235 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 250 seconds with the U filter starting 339 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 19.2 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 0.02. As part of a search for nearby sources, Swift slews to confirm or refute marginal significance events that are near the line-of-sight to nearby galaxies. Based on the lack of a BAT rate trigger, the low significance of the original detection (5.9 sigma) the lack of an XRT detection, and the distance to the suggested host galaxy (12 arcmin) we believe that this event is merely a noise fluctuation in the BAT imager and not an astrophysical event.