TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3938
SUBJECT: GRB 050904 BAT refined analysis of complete data set
DATE:    05/09/07 18:55:04 GMT
FROM:    Jay R. Cummings at NASA/GSFC/Swift  <jayc@milkyway.gsfc.nasa.gov>

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

We now have the complete BAT data for GRB 050904 (Cummings et al.,
GCN circ. 3910 and Palmer et al. GCN circ. 3918).  This was a very
long, bright burst.  The light curve shows 3 main peaks.  There are 
15-second long peaks at ~T+28 sec and ~T+56 sec, and the main peak 
was from ~T+80 sec to ~T+220 sec, along with weaker peaks.  Emission 
in the BAT energy range continues to almost T+500 sec with a weak 
peak at ~T+470 sec.  T90 was 225 +/- 10 sec (estimated error including 
systematics, 15-350 keV).

Fitting a simple power law from T+17 sec to T+226 sec, the photon
index is 1.34 +/- 0.06.  The fluence is 5.4 +/- 0.2 x 10^6 ergs/cm^2.
The 1-second peak flux from T+27.5 sec is 0.8 +- 0.2 photons/cm^2/sec.
All errors are 90% confidence, energy range 15-150 keV.

Haislip et al. (GNC circ. 3914, 3919) reported a Ly-alpha break for 
this burst corresponding to a redshift of 5.3 to 9.0.  Antonelli et al. 
(GCN circ. 3924) calculate a redshift of 6.1.  Kawai et al. (GCN circ.
3937) report a spectrographic redshift of 6.29. With the above fluence 
at this redshift (6.29), the isotropic energy equivalent is 
3.8 x 10^53 ergs in the range 109 - 1094 keV in the GRB rest frame.