TITLE: GCN CIRCULAR NUMBER: 10191 SUBJECT: GRB 091127: Swift detection of a burst DATE: 09/11/27 23:36:19 GMT FROM: David Palmer at LANL E. Troja (NASA/GSFC/ORAU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU), P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), C. Guidorzi (U Ferrara), S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU), J. Mao (INAF-OAB), F. E. Marshall (NASA/GSFC), J. P. Osborne (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL), J. L. Racusin (NASA/GSFC), A. Rowlinson (U Leicester) and M. Stamatikos (OSU/NASA/GSFC) report on behalf of the Swift Team: At 23:25:45 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 091127 (trigger=377179). Swift did not immediately slew to the burst due to Earth limb constraint. The BAT on-board calculated location is RA, Dec 36.571, -18.954 which is RA(J2000) = 02h 26m 17s Dec(J2000) = -18d 57' 12" 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 10 sec. The peak count rate was ~30,000 counts/sec (15-350 keV), at ~1 sec after the trigger. Due to an observing constraint, Swift will not slew until T0+50 minutes. There will be no XRT or UVOT data until this time. Burst Advocate for this burst is E. Troja (eleonora.troja AT 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.)