TITLE: GCN CIRCULAR NUMBER: 17069 SUBJECT: Swift Trigger 618673: probable noise event DATE: 14/11/15 09:40:13 GMT FROM: Caryl Gronwall at PSU/Swift-UVOT W. H. Baumgartner (GSFC/UMBC), M. De Pasquale (INAF-IASFPA), C. Gronwall (PSU), A. Maselli (INAF-IASFPA) and E. Sonbas (NASA/GSFC/Adiyaman Univ.) report on behalf of the Swift Team: At 09:10:35 UT, the Swift Burst Alert Telescope (BAT) triggered and located on trigger 618673. Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 233.024, +32.694 which is RA(J2000) = 15h 32m 06s Dec(J2000) = +32d 41' 38" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed nothing of note for this low significance image trigger. The XRT began observing the field at 09:13:05.1 UT, 149.9 seconds after the BAT trigger. No source was detected in 859 s of promptly downlinked data, which covered 97% of the BAT error circle. 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 153 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 0.03. We believe this trigger to not be from an astrophysical source because of the low significance of the BAT source in the image domain and the lack of an XRT counterpart.