TITLE: GCN CIRCULAR NUMBER: 17394 SUBJECT: Swift Trigger 629693: probably not real DATE: 15/02/04 00:34:54 GMT FROM: David Burrows at PSU/Swift M. H. Siegel (PSU), D. N. Burrows (PSU), N. Gehrels (NASA/GSFC), C. Gronwall (PSU) and B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team: At 00:12:42 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 150204A (trigger=629693). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 207.806, -8.686 which is RA(J2000) = 13h 51m 13s Dec(J2000) = -08d 41' 08" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). This was an image trigger and, as usual for such events, does not show any noticeable structure. The XRT began observing the field at 00:15:04.5 UT, 141.7 seconds after the BAT trigger. No source was detected in 468 s of promptly downlinked data. We are waiting for the full dataset to detect and localise the XRT counterpart. UVOT took a finding chart exposure of 58 seconds with the White filter starting 858 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 0.04. Given the lack of a bright XRT source, it is likely that this is a noise event and not an astrophysical source. The full ground-linked data set will be necessary to verify. Burst Advocate for this burst is M. H. Siegel (siegel AT swift.psu.edu). 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.)