GCN Circular 2723

XRF 040912 (=H3557):  Spectral and Temporal Properties

J-F Olive, G. Ricker, J-L. Atteia, N. Kawai, D. Lamb, and S. Woosley,
on behalf of the HETE Science Team;

T. Donaghy, E. Fenimore, M. Galassi, C. Graziani, M. Matsuoka,
Y. Nakagawa, T. Sakamoto, R. Sato, Y. Shirasaki, M. Suzuki,
T. Tamagawa, Y. Urata, T. Yamazaki, Y. Yamamoto, and A. Yoshida, on
behalf of the HETE WXM Team;

N. Butler, G. Crew, J. Doty, A. Dullighan, 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;

C. Barraud, M. Boer, J-P Dezalay, and K. Hurley, on behalf of the HETE
FREGATE Team;

report:

The burst-average photon number spectrum of GRB 040912 is best fit by
a power-law times exponential (PLE) model with a photon index alpha =
1.75 +0.28/-0.30 and a peak energy E_peak = 14.5 +/-14.5 keV.

The fluence of the burst is (8.3 +1.4/-1.3 ) x 10-7 erg cm-2 in the 2-30
keV energy band and (3.3 +2.9/-1.7) x 10-7 erg cm-2 in the 30-400 keV
energy band.  The ratio of the fluences in the two energy bands is 2.5,
clearly making this burst an X-Ray Flash.

The T50 and T90 durations of XRF 040912 are 80 +/-5 sec and 127 +/-13
sec in the 6-40 keV energy band, and 81 +/-5 sec and 122 +/-7 sec in the
6-80 keV energy band, respectively.

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