TITLE: GCN CIRCULAR NUMBER: 17061 SUBJECT: Swift Trigger 618402: probable noise event DATE: 14/11/12 10:14:17 GMT FROM: Craig Markwardt at NASA/GSFC M. G. Bernardini (INAF-OAB), P. D'Avanzo (INAF-OAB), D. Malesani (DARK/NBI) and C. B. Markwardt (NASA/GSFC) report on behalf of the Swift Team: At 09:06:27 UT, the Swift Burst Alert Telescope (BAT) triggered and located image trigger 618402. Swift slewed immediately to the location. The BAT on-board calculated location is RA, Dec 189.977, +15.479 which is RA(J2000) = 12h 39m 55s Dec(J2000) = +15d 28' 44" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve does not show any significant variation, which is typical for an image trigger. The on-board image significance is 6.3 sigma, which is below the threshold for declaring a burst. However, ground-based processing does find a slightly improved significance of 6.5 sigma. More information will be known after processing the full BAT data set. The XRT began observing the field at 09:08:42.0 UT, 134.8 seconds after the BAT trigger. No X-ray source was detected in 590 s of promptly-downlinked data, suggesting that the initial on-board centroid was likely due to a cosmic ray. 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. Results from the list of sources generated on-board are not available at this time. This was a low-significance image trigger in the direction of NGC 4595. However, NGC 4595 is 11 arc minutes from the center of the BAT error circle (error circle radius 3 arcminutes), so the association is unlikely. Given the lack of detection of XRT or UVOT counterparts, this trigger is likely the result of a noise fluctuation.