TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  5520
SUBJECT: GRB 060904B:  Swift-BAT refined analysis
DATE:    06/09/04 15:45:45 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>

C. Markwardt (GSFC/UMD), L. Barbier (GSFC), S. D. Barthelmy (GSFC),
J. Cummings (GSFC/UMD), E. Fenimore (LANL), N. Gehrels (GSFC),
D. Grupe (PSU), D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA),
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU),
G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC)
on behalf of the Swift-BAT team:
 
Using the data set from T-239 to T+807 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 060904B (trigger #228006)
(Grupe, et al., GCN Circ. 5505).  The BAT ground-calculated position is
RA,Dec = 58.218, -0.729 deg {3h 52m 52.3s, 0d 43' 45.0"} (J2000) +- 0.9 arcmin,
(radius, sys+stat, 90% containment).  The partial coding was 50%.
 
The mask-weighted lightcurve shows the burst starting at ~T-2 sec
with a FRED peak shape (halfwidth ~9 sec) with a return to background level
at ~T+50 sec.  Then a second, weaker peak starts at ~T+120 sec, peaks 
at ~T+155 sec and is done by ~T+220 sec.  T90 (15-350 keV) is 192 +- 5 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-0.9 to T+212.8 is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.70 +- 0.14.  The fluence in the 15-150 keV band is 1.7 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+1.16 sec in the 15-150 keV band
is 2.5 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence level.