TITLE: GCN CIRCULAR NUMBER: 18659 SUBJECT: GRB 151205B: Swift detection of a burst DATE: 15/12/05 21:51:08 GMT FROM: David Palmer at LANL F. E. Marshall (NASA/GSFC), P. D'Avanzo (INAF-OAB), C. Gronwall (PSU), L. M. Z. Hagen (PSU), H. A. Krimm (CRESST/GSFC/USRA), A. Melandri (INAF-OAB), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 21:43:14 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 151205B (trigger=666378). Swift could not slew immediately to the burst due to an observing contraint. The BAT on-board calculated location is RA, Dec 41.158, -43.481 which is RA(J2000) = 02h 44m 38s Dec(J2000) = -43d 28' 49" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single-peaked structure with a duration of about 5 sec. The peak count rate was ~1800 counts/sec (15-350 keV), at ~0 sec after the trigger. Due to an observing constraint, Swift will not slew until T0+50.6 minutes. There will be no XRT or UVOT data until this time. 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.)