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GCN Circular 5639

GRB 060927, Swift-BAT refined analysis
2006-09-27T22:40:03Z (18 years ago)
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.
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