TITLE: GCN GRB OBSERVATION REPORT
NUMBER: 1600
SUBJECT: HETE fluences for GRB021004
DATE: 02/10/07 21:06:11 GMT
FROM: Don Lamb at U.Chicago
D. Lamb, G. Ricker, J-L Atteia, N. Kawai, and S. Woosley on behalf of
the HETE Science Team;
J-F Olive, M. Boer, J-P Dezalay, and K. Hurley on behalf of the HETE
FREGATE Team;
Y. Shirasaki, M. Matsuoka, T. Tamagawa, K. Torii, T. Sakamoto,
A. Yoshida, E. Fenimore, M. Galassi, T. Tavenner, C. Graziani, and
T. Donaghy, on behalf of the HETE WXM Team;
J. Villasenor, R. Vanderspek, J. Doty, G. Crew, G. Monnelly, N. Butler,
T. Cline, J.G. Jernigan, A. Levine, F. Martel, E. Morgan, G. Prigozhin,
G. Azzibrouck, J. Braga, R. Manchanda, and G. Pizzichini, on behalf of
the HETE Operations and HETE Optical-SXC Teams;
write:
Analysis of the FREGATE data for GRB021004 (=H2380) shows that
the fluence-averaged photon number spectrum of the burst is well-fit
by a single power-law spectrum with slope alpha = 1.64 +/- 0.09, and
gives the following values for the fluences of the burst:
S = 1.8 x 10-6 erg cm-2 (50-300 keV), and
S = 3.2 x 10-6 erg cm-2 (7-400 keV).
Using the latter value and assuming Omega_Lambda = 0.7, Omega_m = 0.3,
and H_0 = 70 km s-1 Mpc-1, the isotropic-equivalent energy of the
burst is
E_iso = 2.06 x 10^(52) ergs.
Using this value of E_iso and equation (1) of Frail et al. (ApJ 562,
L55, 2001) [see also Sari et al. (ApJ 519, L17, 1999)] to estimate the
jet break time, we find
t_j = 1.3 [(1+z)/2.60] (theta_j/0.070)^(8/3) [E_iso/2 x 10^(52) ergs]
x (eta/0.2)^(-1/8) (n/0.1 cm-3)^(-1/8) days.
Analysis of the WXM data for GRB021004 gives the following value for the
fluence of the burst in the WXM energy band:
S = 7.5 x 10-7 erg cm-2 (2-25 keV).
The fluence ratio S(2-25)/S(50-300)= (7.5 x 10-7)/(1.8 x 10-6) = 0.42
implies that GRB021004 is an X-ray rich GRB [log (S_x/S_gamma) > -0.5].
This message is citable.