TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3284 SUBJECT: GRB 050416b: Swift-BAT refined analysis DATE: 05/04/17 03:26:08 GMT FROM: Takanori Sakamoto at NASA/GSFC G. Sato (ISAS), L. Barbier, S. Barthelmy (GSFC), J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (UMD), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), M. Suzuki (Saitama), J. Tueller (GSFC) on behalf of the Swift-BAT team: At 22:35:54.1 UT Swift-BAT detected GRB 050416b (trigger=114797) (GCN Circ 3279, Hullinger et al.). The refined BAT ground position is (RA,Dec) = 133.854, 11.182, [deg; J2000] +- 3 arcmin, (95% containment). The partial coding fraction was 16%. The moon is moving towards the position of the GRB, and Swift will not be able to observe for several days because of the spacecraft moon angle constraint. The BAT mask weighted light curve shows a FRED-like structure. T90 (15-350 keV) is (5.4 +- 0.9) seconds (estimated error including systematics). The time-averaged spectrum is well fitted in a simple power-law model. The photon index is 1.5 +- 0.2. The fluence in the 15-350 keV band is (2.1 +- 0.3) x 10^-6 erg/cm2. The peak photon flux in the 15-350 band is (7.9 +- 0.7) ph/cm2/s. The quoted errors are at the 90% confidence level.