TITLE: GCN GRB OBSERVATION REPORT NUMBER: 2992 SUBJECT: GRB050128 Swift-BAT observations DATE: 05/01/28 11:10:10 GMT FROM: Neil Gehrels at GSFC J. Cummings (GSFC), G. Sato (ISAS), L. Antonelli (INAF-OAR), S. Barthelmy, L. Barbier (GSFC), P. Boyd (GSFC-UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (GSFC/UMD), H. Krimm (GSFC/USRA), F. Marshall (GSFC), C. Markwardt (GSFC/UMD), K. McLean (LANL), M. Capalbi (ASDC), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC), M. Suzuki (Saitama), J. Tueller (GSFC), S. Zane (MSSL) on behalf of the Swift-BAT team: At 04:19:54 UT, the Swift Burst Alert Telescope (BAT) triggered and located on-board GRB050128. The spacecraft autonomously slewed to the burst and an x-ray afterglow source was detected by XRT (GCN 2991, Antonelli et al.). The BAT on-board calculated location is RA,Dec 219.587, -34.762 (J2000) with an uncertainty of 3 arcmin (radius, 3-sigma, including a systematic uncertainty dominated by the GRB being 51 deg off axis). This is 39 arcsec from the XRT position. The lightcurve is multi-peaked with a T90 duration of 13.8 sec. The fluence is 4.5e-6 erg/cm^2 and the peak flux (1 sec interval) is 4.6 ph/cm^2/s in the 15-350 keV band. The spectrum is consistent with a power-law of photon index 1.5 +- 0.05. [GCN OPS NOTE (28jan05): As per D.Burrows request, the "C.Milvia" was changed to "M. Capalbi".]