TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4864 SUBJECT: GRB 060312: Refined analysis of the Swift-BAT burst DATE: 06/03/12 17:09:19 GMT FROM: Scott Barthelmy at NASA/GSFC H. Krimm (GSFC/USRA), L. Barbier (GSFC), S. Barthelmy (GSFC), J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Grupe (PSU), D. Hullinger (BYU-Idaho), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), G. Sato (ISAS), J. Tueller (GSFC) on behalf of the Swift-BAT team: Using the data set from T-300 to T+302 sec from the recent telemetry downlink, we report further analysis of BAT GRB 060312 (trigger #201391) (Grupe, et al., GCN 4859). The BAT ground-calculated position is RA,Dec = 45.777,+12.825 deg {3h 3m 6.5s,+12d 49' 29.6"} (J2000) +- 0.9 arcmin, (radius, sys+stat, 90% containment). The partial coding was 100%. The mask-weighted lightcurve shows two main peaks at T-27 and T+7 sec. The first peak starts at T-35 sec and the second ends at ~T+30 sec. T90 (15-350 keV) is 43 +- 3 sec (estimated error including systematics). The time-averaged spectrum from T-29.4 to T+22.0 is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.35 +- 0.34, and Epeak of 62.8 +- 21.5 keV (chi squared 46.33 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 1.8 +- 0.1 x 10^-06 erg/cm2 and the 1-sec peak flux measured from T+5.63 sec in the 15-150 keV band is 1.5 +- 0.1 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.85 +- 0.08 (chi squared 52.99 for 57 d.o.f.). All the quoted errors are at the 90% confidence level.