GCN Circular 3938
Subject
GRB 050904 BAT refined analysis of complete data set
Date
2005-09-07T18:55:04Z (20 years ago)
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.