[vsnet-grb-info 7498] GRB 090328: Fermi GBM Spectral Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9057
SUBJECT: GRB 090328: Fermi GBM Spectral Analysis
DATE:    09/03/30 20:10:37 GMT
FROM:    Arne Rau at MPE  <arau at mpe.mpg.de>

Arne Rau (MPE), Valerie Connaughton (UAH) and Michael Briggs (UAH) 
report on behalf of the Fermi GBM team:

"We have performed spectral analysis of the GBM data for GRB 090328 (GCN 
9044).

The spectrum from T0+3.1s to T0+29.7s is best fit by a Band function 
with indices alpha=-0.93 +/- 0.02 and beta=-2.2 +/- 0.1, and peak energy 
of Epeak=653 +/- 45 keV (chi squared 365 for 311 d.o.f.). At a redshift 
of 0.736 (GCN 9053), the Epeak in the GRB rest frame, Epeak_rest, is 
1133 +/- 0.078 MeV.

The event fluence in this time interval is (8.09 +/- 0.10)E-5 erg/cm^2 
in the 8-1000 keV band and (9.5 +/- 1.0)E-5 erg/cm^2 in the 8keV-40MeV 
band. Using standard cosmology (Omega_matter = 0.27, Omega_lambda = 
0.73, H0=71) the isotropic equivalent energy in the 8keV-40MeV band is 
E_iso = (2.3 +/- 0.2)E+53 ergs. The 1-sec peak photon flux measured 
starting from T0+23.5 s in the 8-1000 keV band is 18.5 +/- 0.5 ph/s/cm^2.

This time interval consists of three main emission peaks, from T0+3.1s 
to T0+8.2s, from T0+13.3s to T0+19.5s, and from T0+23.6 to T0+25.6s. All 
of these shorter intervals are also best fit by a Band function. For the 
first interval the power-law indices are alpha=-0.79 +/- 0.04 and 
beta=-2.3 +/- 0.2, Epeak is 648 +/- 68 keV, Epeak_rest is 1125 +/- 118 
keV, and the fluence (8-1000 keV) is (3.80 +/- 0.08)E-06. For the second 
interval the power-law indices are alpha=-0.86 +/- 0.03, beta=-2.3 +/- 
0.2, Epeak is 676 +/- 62 keV, Epeak_rest is 1174 +/- 108 keV, and the 
fluence (8-1000 keV) is (4.35 +/- 0.07)E-6. For the third interval the 
power-law indices are alpha=-0.94 +/- 0.05, beta=-2.4 +/- 0.3, Epeak is 
481 +/- 60 keV, Epeak_rest is 835 +/- 104 keV, and the fluence (8-1000 
keV) is (4.3 +/- 0.1)E-6.

The spectral analysis results presented above are preliminary; final 
results will be published in the GBM GRB Catalog."