TITLE: GCN CIRCULAR NUMBER: 22928 SUBJECT: Trigger 846740: Swift trigger near NGC5055 DATE: 18/07/08 13:55:21 GMT FROM: Scott Barthelmy at NASA/GSFC S. D. Barthelmy (GSFC), A. D'Ai (INAF-IASFPA), V. D'Elia (ASDC), S. W. K Emery (UCL-MSSL), J.D. Gropp (PSU), N. P. M. Kuin (UCL-MSSL), S. J. LaPorte (PSU), A. Y. Lien (GSFC/UMBC) and A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 13:33:38 UT, the Swift Burst Alert Telescope (BAT) triggered and located a low significance source (trigger=846740). Swift slewed immediately to the location. The BAT on-board calculated location is RA, Dec 198.919, +41.897, which is RA(J2000) = 13h 15m 41s Dec(J2000) = +41d 53' 50" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is typical for image triggers, the real time light curve does not show anything significant. Further, this trigger is very weak with a 5.93 sigma in the image domain. This low-significance trigger was due to being near NGC5055. The XRT began observing the field at 13:36:28.0 UT, 169.3 seconds after the BAT trigger. No source was detected in 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 173 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. Given the low significance in BAT and the lack of a detection in XRT, we believe this to be a noise fluctuation trigger near a known galaxy (NGC5055). Further analysis will be done when the full data set is downloaded.