TITLE: GCN CIRCULAR NUMBER: 16204 SUBJECT: Swift Trigger 597860 is probably not a GRB DATE: 14/05/02 14:33:31 GMT FROM: David Palmer at LANL V. Mangano (PSU), M. M. Chester (PSU), P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), S. T. Holland (STScI), J. A. Kennea (PSU), A. Y. Lien (NASA/GSFC/ORAU) and D. M. Palmer (LANL) report on behalf of the Swift Team: At 14:13:56 UT, the Swift Burst Alert Telescope (BAT) triggered on a peak in an image (trigger=597860). Swift slewed immediately to the location. The BAT on-board calculated location is RA, Dec 199.681, -35.631 which is RA(J2000) = 13h 18m 43s Dec(J2000) = -35d 37' 50" 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 BAT light curve. The XRT began observing the field at 14:16:14.9 UT, 139.0 seconds after the BAT trigger. No source was detected in 772 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 150 seconds with the White filter starting 142 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 0.05. Due to the marginal detection in BAT (7.06 sigma) with no corresponding rate increase, and the lack of a detection in XRT and UVOT, we believe that this is probably not an astrophysical source. Final determination of the reality of the source will require the full downlinked data. Burst Advocate for this burst is V. Mangano (vxm22 AT psu.edu). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.)