[vsnet-grb-info 2306] GRB 051022: Spectral Analysis Indicates That
The Spectrum Is Absorbed
GCN Circulars
gcncirc at capella.gsfc.nasa.gov
Sun Oct 23 13:07:05 JST 2005
TITLE: GCN GRB OBSERVATION REPORT
NUMBER: 4145
SUBJECT: GRB 051022: Spectral Analysis Indicates That The Spectrum Is Absorbed
DATE: 05/10/23 04:04:49 GMT
FROM: Don Lamb at U.Chicago <lamb at oddjob.uchicago.edu>
GRB 051022: Spectral Analysis Indicates That The Spectrum Is Absorbed
J. Doty, G. Ricker, J-L. Atteia, N. Kawai, D. Lamb, and S. Woosley, on
behalf of the HETE Science Team;
M. Arimoto, T. Donaghy, E. Fenimore, M. Galassi, C. Graziani,
N. Ishikawa, A. Kobayashi, J. Kotoku, M. Maetou, M. Matsuoka,
Y. Nakagawa, T. Sakamoto, R. Sato, T. Shimokawabe, Y. Shirasaki,
S. Sugita, M. Suzuki, T. Tamagawa, K. Tanaka, and A. Yoshida, on behalf
of the HETE WXM Team;
N. Butler, G. Crew, G. Prigozhin, R. Vanderspek, J. Villasenor,
J. G. Jernigan, A. Levine, G. Azzibrouck, J. Braga, R. Manchanda,
and G. Pizzichini, on behalf of the HETE Operations and HETE
Optical-SXC Teams;
M. Boer, J-F Olive, J-P Dezalay, and K. Hurley, on behalf of the HETE
FREGATE Team;
report:
We have performed a spectral analysis of the WXM and FREGATE spectral
data for GRB 051022. Fitting a power-law times exponential (PLE) model
jointly to the WXM and FREGATE spectral data yields a chi^2 of 185 for
139 DOF, while fitting a PLE model with absorption yields a chi^2 of
131 for 138 DOF. Fitting a Band model jointly to the WXM and FREGATE
spectral data also yields a chi^2 of 131 for 138 DOF. These results
show that the data strongly favor a PLE model with absorption over a
PLE model alone, and that a PLE model with absorption gives a
satisfactory fit to the data. They also show that the data do not
request a Band model with absorption.
The best-fit spectral parameters for the PLE model with absorption are
alpha = -1.22+/-0.02, E_peak = 306 + 31/-26 keV, and n_H = 1.7 ± 0.4
x 10^22 atoms cm^-2. The fluence is (2.2 ± 0.02) x 10^-5 erg cm^-2
in the 2-30 keV energy band and (1.4 ± 0.02) x 10^-4 erg cm^-2 in the
30-400 keV energy band. The ratio log(S_x/S_g) = -1.8, so GRB 051022
is a "classical" hard GRB.
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