TITLE: GCN CIRCULAR NUMBER: 19780 SUBJECT: Swift Trigger 707517 is probably not a GRB DATE: 16/08/06 05:41:29 GMT FROM: David Palmer at LANL J. L. Racusin (NASA/GSFC), P. D'Avanzo (INAF-OAB), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), A. Melandri (INAF-OAB), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 05:18:31 UT, the Swift Burst Alert Telescope (BAT) triggered and located a marginal peak (trigger=707517). Swift slewed immediately to the location. The BAT on-board calculated location is RA, Dec 98.208, -22.786 which is RA(J2000) = 06h 32m 50s Dec(J2000) = -22d 47' 08" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As with most image triggers, there is no obvious variation in the immediately-available BAT lightcurve. The XRT began observing the field at 05:20:37.4 UT, 126.1 seconds after the BAT trigger. No source was detected in 867 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 338 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. No correction has been made for the expected extinction corresponding to E(B-V) of 0.09. Due to the lack of a rate increase in BAT, the marginal nature of the peak (7.15 sigma) and the lack of an XRT afterglow, we believe that this is probably not a GRB. A final determination will require the complete downlinked dataset. Burst Advocate for this burst is J. L. Racusin (judith.racusin AT nasa.gov). 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.)