GCN Circular 9057
Subject
GRB 090328: Fermi GBM Spectral Analysis
Date
2009-03-30T20:10:37Z (16 years ago)
From
Arne Rau at MPE <arau@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."