TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4671
SUBJECT: GRB 060204B: Swift-BAT refined analysis
DATE:    06/02/05 04:41:50 GMT
FROM:    Takanori Sakamoto at NASA/GSFC  <takanori@milkyway.gsfc.nasa.gov>

C. Markwardt (GSFC/UMD), L. Barbier (GSFC), S. Barthelmy (GSFC), 
J. Cummings (GSFC/ORAU), E. Fenimore (LANL), N. Gehrels (GSFC), 
D. Hullinger (UMD), H. Krimm (GSFC/USRA), F. Marshall (GSFC),  
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), 
G. Sato (ISAS), T. Takahashi (ISAS), J. Tueller (GSFC), 
on behalf of the Swift-BAT team:

Using the data set from T-299.1 to T+303.0 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 060204B
(trigger #180241)  (Falcone, et al., GCN 4655).  The BAT ground-calculated 
position is (RA,Dec) = 211.812, 27.675  deg {14h 7m 14.9s, 27d 40' 29.1"} 
(J2000) +- 0.8 arcmin, (radius, sys+stat, 90% containment).  
The partial coding was 77%.
 
The mask-weighted light curve shows a strong peak with a slow rise starting 
from T-30 sec to T+5 sec, and a faster decay till T+30 sec.  The weak emission 
extends to T+120 sec, and there is a small peak at T+120 sec.  There is a 
possible precursor at T-165 sec with a width of ~20 sec.  T90 (15-350 keV) 
is (134 +- 5) sec (estimated error including systematics).
 
The time-averaged spectrum from T-24.4 to T+170.7 is best fit by 
a power law with an exponential cutoff.  This fit gives a photon index 
0.82 +- 0.40, and Epeak of 96.8 +- 41.0 keV (chi squared 38.83 for 56 d.o.f.).  
For this model the total fluence in the 15-150 keV band is 
(3.0 +- 0.2) x 10^-06 erg/cm2 and the 1-sec peak flux measured from T+5.04 sec 
in the 15-150 keV band is (1.3 +- 0.2) ph/cm2/sec.  A fit to a simple power law 
gives a photon index of 1.46 +- 0.09 (chi squared 47.69 for 57 d.o.f.).  
All the quoted errors are at the 90% confidence level.