TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5011 SUBJECT: GRB 060427: Refined analysis of the Swift-BAT burst DATE: 06/04/27 21:21:57 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. Hullinger (BYU-Idaho), V. Mangano (INAF-IASFPA), 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-239 to T+963 sec from recent telemetry downlinks, we report further analysis of BAT GRB 060427 (trigger #207281) (Mangano, et al., GCN 5006). The BAT ground-calculated position is RA,Dec = 124.175,+62.654 deg {8h 16m 42.0s,+62d 39' 13.4"} (J2000) +- 2.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 71%. The mask-weighted lightcurve shows a broad peak starting at ~T-20 sec and lasting to ~T+80 sec. T90 (15-350 keV) is 64 +- 5 sec (estimated error including systematics). The time-averaged spectrum from T-10.0 to T+60.0 is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.87 +- 0.29. The fluence in the 15-150 keV band is 5.0 +- 0.9 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T+5.00 sec in the 15-150 keV band is 0.3 +- 0.1 ph/cm2/sec. All the quoted errors are at the 90% confidence level.