GCN Circular 3019

GRB 050209(=U11568):  Duration and spectrum

D. Lamb, G. Ricker, J-L. Atteia, N. Kawai, 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, 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:

The T_50 durations for GRB 050209 are approximately 16, 17, and 15 s in
the 6-40, 6-80 and 30-400 keV energy bands, respectively; the T_90 
durations for the burst are approximately 36, 41, and 46 s in the same
energy bands.

The spectrum of GRB 050209 evolves strongly from hard to soft during
the burst.  Ground analysis of the FREGATE and WXM spectral data show
that the average spectrum of the burst is adequately fit by a single
power-law with index alpha = - 1.7 � 0.07 in the 2-400 keV energy band,
implying that E_0 lies near or above 400 keV and E_peak lies above 120
keV.  The fluences in the 2-30 keV and 30-400 keV energy bands are 1 x
10-6 and 2 x 10-6 erg cm-2, respectively; the fluence in the 2-400 keV
energy band is therefore 3 x 10-6 erg cm-2.  The fluence ratio 
S(2-30 keV)/S(30-400 kev) = 0.33.  Technically, this makes GRB 050209 
an "X-ray rich" burst, despite the relatively high value of E_peak.  
This is due to the steepness of the low-energy power-law index alpha. 
Because we are only able to place a lower bound on E_peak, we can only
place a lower limit on the pseudo-redshift for this burst of about 2.

A light curve, skymap, and some spectral information for GRB 050209 are
provided at the following URL:

http://space.mit.edu/HETE/Bursts/GRB050209

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