TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3793 SUBJECT: GRB 050813: Swift-BAT refined analysis DATE: 05/08/13 19:01:47 GMT FROM: Craig Markwardt at NASA/GSFC/UMD G. Sato (ISAS), L. Angelini (GSFC-JHU), L. Barbier (GSFC), S. Barthelmy (GSFC), J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC), J. Grenier (MPE), D. Hullinger (UMD), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), T. Mitani (ISAS), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), G. Sato (ISAS), M. Suzuki (Saitama), J. Tueller (GSFC), on behalf of the Swift/BAT team: At 06:45:09.76 UT Swift-BAT detected GRB 050813 (trigger=150139) (GCN Circ 3788, Retter et al.). The refined BAT ground position is (RA,Dec) = 241.988, +11.246, [deg; J2000] +- 3 arcmin, (95% containment radius). The partial coding was 57%. This is 7 arcsec from the XRT position (Morris et al., GCN 3790). The burst has a short spike lasting ~32 msec, overlayed on broader peak of duration ~0.6 sec. There is a hint of a second peak at T+1.3 seconds. T90 (15-350 keV) is (0.6 +- .1) seconds (estimated error including systematics). The photon index of the time-averaged spectrum is 1.19 +- 0.33. The fluence in the 15-350 keV band is (1.24 +- 0.46) x 10^-7 erg/cm2. The 1-s peak photon flux measured from T+0.1 second in the 15-350 band is (1.22 +- 0.26) ph/cm2/s. All the quoted errors are at the 90% confidence level.