TITLE: GCN CIRCULAR NUMBER: 20199 SUBJECT: Swift Trigger 723124 is probably not a GRB DATE: 16/11/21 02:40:22 GMT FROM: David Palmer at LANL F. E. Marshall (NASA/GSFC), A. D'Ai (INAF-IASFPA), V. D'Elia (ASDC), A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 02:17:34 UT, the Swift Burst Alert Telescope (BAT) triggered on a peak in a waiting mode image (trigger=723124). Swift slewed immediately to the location. The BAT on-board calculated location is RA, Dec 176.394, -6.896 which is RA(J2000) = 11h 45m 35s Dec(J2000) = -06d 53' 46" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is usual for an image trigger, no BAT count rate variation is visible in the immediately available data. The XRT began observing the field at 02:19:29.6 UT, 114.9 seconds after the BAT trigger. No source was detected in 599 s of promptly downlinked data. We are waiting for the full dataset to detect and localise any XRT counterpart. UVOT took a finding chart exposure of 150 seconds with the White filter starting 116 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. Due to the marginal significance of the peak in the BAT image (7.16 sigma) the lack of an increase in the BAT count rates, and the non-detection of an afterglow by XRT, we believe that this is probably a statistical fluctuation and not an astrophysical event. Determination of the reality of this trigger will require the complete downlinked dataset. Burst Advocate for this burst is F. E. Marshall (marshall AT milkyway.gsfc.nasa.gov). 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.)