TITLE: GCN CIRCULAR NUMBER: 30929 SUBJECT: Swift Trigger 1078701 is probably not a GRB DATE: 21/10/10 11:00:39 GMT FROM: David Palmer at LANL <palmer@lanl.gov> M. G. Bernardini (INAF-OAB), P. D'Avanzo (INAF-OAB), N. J. Klingler (GSFC/UMBC/CRESSTII), A. Y. Lien (U Tampa), A. Melandri (INAF-OAB), K. L. Page (U Leicester), D. M. Palmer (LANL) and T. Sbarrato (INAF-OAB) report on behalf of the Neil Gehrels Swift Observatory Team: At 10:42:36 UT, the Swift Burst Alert Telescope (BAT) triggered on an event with marginal significance (trigger=1078701). Swift slewed immediately to the location. The BAT on-board calculated location is RA, Dec 287.080, +29.822 which is RA(J2000) = 19h 08m 19s Dec(J2000) = +29d 49' 19" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve doesn't show anything significant. The XRT began observing the field at 10:44:08.6 UT, 92.8 seconds after the BAT trigger. No source was detected in 127 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 138 seconds with the White filter starting 97 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 0.231. Due to the marginal detection significance in both BAT rates and on-board image (6.48 and 6.50 sigma respectively) with no detection in the ground image analysis, and the lack of detection by XRT, we believe that this is probably a noise fluctuation in BAT and not an astrophysical event.