TITLE: GCN CIRCULAR NUMBER: 7632 SUBJECT: GRB 080420?: Swift detection of a possible short burst DATE: 08/04/20 04:37:41 GMT FROM: David Palmer at LANL L. Vetere (PSU), D. N. Burrows (PSU), M. M. Chester (PSU), D. Grupe (PSU), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), C. B. Markwardt (CRESST/GSFC/UMD), C. Pagani (PSU), D. M. Palmer (LANL), J. L. Racusin (PSU), M. Stamatikos (NASA/ORAU) and M. C. Stroh (PSU) report on behalf of the Swift Team: At 04:12:47 UT, the Swift Burst Alert Telescope (BAT) triggered and located possible GRB 080420 (trigger=309665). Swift slewed immediately to the calculated location. The BAT on-board calculated location is RA, Dec 152.639, +43.242 which is RA(J2000) = 10h 10m 33s Dec(J2000) = +43d 14' 33" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single spike structure in a single 64 msec bin. The peak count rate was ~1300 counts/sec (15-350 keV), at ~0 sec after the trigger. Because of the low significance of the detection (6.6 sigma) we cannot positively confirm that this is a real event until we receive the downlinked data from Malindi around 10:00 UT. The XRT began observing the source at 04:13:42 UT, 54 s after the BAT trigger. The on-board detection algorithm did not centroid on a source due to insufficient counts so no prompt X-ray position is available at the moment. No source is seen in 300 seconds of promptly downloaded data; therefore any X-ray source is extremely faint. No further data will be available until about 10 UT. UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 57 seconds after the BAT trigger, and an exposure of 400 seconds with the V filter starting 163 seconds after the BAT trigger. No 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 18.5 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 0.01. Burst Advocate for this burst is L. Vetere (vetere AT astro.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.) [GCN OPS NOTE(21apr08): Per author's request, the "~2000 counts/sec" in the first paragraph was changed to "~1300 counts/sec".]