TITLE: GCN CIRCULAR NUMBER: 15323 SUBJECT: Trigger 574266 is not a Swift detection of a known source DATE: 13/10/11 22:55:55 GMT FROM: David Palmer at LANL A. P. Beardmore (U Leicester), J. R. Cummings (NASA/UMBC), N. Gehrels (NASA/GSFC), A. Y. Lien (NASA/GSFC/ORAU), C. J. Mountford (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 22:16:58 UT, the Swift Burst Alert Telescope (BAT) triggered on a rate increase (trigger=574266), and produced an image. This image included a statistically marginal peak which was 6 arcminutes from the RS CVn source VY Ari. Swift slewed immediately to the peak location. The BAT on-board calculated location is RA, Dec 42.286, +7.440 which is RA(J2000) = 02h 49m 09s Dec(J2000) = +07d 26 24 with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi-peaked structure with a duration of about 30 sec, starting gradually at about T-20. The peak count rate was ~3386 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 22:18:47.5 UT, 109.3 seconds after the BAT trigger. No source was detected in 957 s of promptly downlinked data, which covered 84% 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 113 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 0.22. When a marginal BAT image peak is found near to a previously-known source, Swift is programmed to make follow-up observations to test whether the detection is real. In this case, the strength of the rate variation in the BAT light curve is inconsistent with the low significance of the image peak location, and the peak location is outside of the expected BAT error circle for the VY Ari source. For these reasons, we believe that VY Ari is not the source of the BAT lightcurve variations, which may be due to a GRB outside of the BAT FOV. Burst Advocate for this burst is A. P. Beardmore (apb AT star.le.ac.uk). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.)