TITLE: GCN CIRCULAR NUMBER: 16692 SUBJECT: Swift Trigger 609694 is probably not an astrophysical source DATE: 14/08/16 18:50:38 GMT FROM: David Palmer at LANL J. R. Cummings (NASA/UMBC), N. Gehrels (NASA/GSFC), C. Gronwall (PSU), J. A. Kennea (PSU), D. M. Palmer (LANL) and B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team: At 18:34:11 UT, the Swift Burst Alert Telescope (BAT) located a marginal significance (5.84 sigma) image peak in the vicinity of the known source IGR J16185-5928 (trigger=609694) in an untriggered image. Swift slewed immediately to the location in order to confirm or refute the event. The BAT on-board calculated location is RA, Dec 244.998, -59.389 which is RA(J2000) = 16h 19m 59s Dec(J2000) = -59d 23' 21" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is usual for images without a corresponding rate trigger, no obvious variation is visible in the BAT rates lightcurve. The XRT began observing the field at 18:36:33.1 UT, 141.5 seconds after the BAT trigger. No source was detected in 443 s of promptly downlinked data, which covered 93% 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 144 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. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the sub-image. The 8'x8' region for the list of sources generated on-board covers 53% of the BAT error circle. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the region. No correction has been made for the expected extinction corresponding to E(B-V) of 0.26. Due to the marginal significance of the detection (5.84 sigma), the lack of a corresponding rate trigger, the large distance of the image peak from the known source (12 arcminutes), and the lack of a corresponding source in the XRT and UVOT instruments, we believe that this is a statistical fluctuation in image space rather than an astrophysical source.