TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5639 SUBJECT: GRB 060927, Swift-BAT refined analysis DATE: 06/09/27 22:40:03 GMT FROM: Scott Barthelmy at NASA/GSFC M. Stamatikos (GSFC/ORAU), L. Barbier (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), J. Tueller (GSFC) on behalf of the Swift-BAT team: Using the data set from T-240 to T+362 sec from recent telemetry downlinks, we report further analysis of BAT GRB 060927 (trigger #231362) (Barbier, et al., GCN Circ. 5627). The BAT ground-calculated position is RA,Dec = 329.547, 5.369 deg {21h 58m 11.3s, 5d 22' 9.4"} (J2000) +- 0.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 82%. The masked-weighted lightcurves starts with two overlapping peaks at T-2 sec, and returning to background at T+9 sec. The third peak starts at T+15 sec and ends at T+24 sec. T90 (15-350 keV) is 22.6 +- 0.3 sec (estimated error including systematics). The time-averaged spectrum from T-1.0 to T+23.8 is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.93 +- 0.38, and Epeak of 71.7 +- 17.6 keV (chi squared 64.6 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 1.1 +- 0.1 x 10^-06 erg/cm2 and the 1-sec peak flux measured from T+0.17 sec in the 15-150 keV band is 2.8 +- 0.2 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.65 +- 0.08 (chi squared 77.5 for 57 d.o.f.). All the quoted errors are at the 90% confidence level.