GCN Circular 1280

GRB020317 (=H1959): Localization by HETE of a Low Fluence GRB 
Exhibiting Strong Spectral Evolution

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

J. Villasenor, R. Vanderspek, G. Crew, J. Doty, G. Monnelly, N. 
Butler, T. Cline, J.G. Jernigan, A. Levine, F. Martel, E. Morgan, G. 
Prigozhin, J. Braga, R. Manchanda, and G. Pizzichini, on behalf of 
the HETE Operations and HETE Optical-SXC Teams;

M. Matsuoka, Y. Shirasaki, T. Tamagawa, K. Torii, T. Sakamoto, A. 
Yoshida, E. Fenimore, M. Galassi, T. Tavenner, T. Donaghy, and C. 
Graziani, on behalf of the HETE WXM Team;

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

write:

At 18:15:31.42 UTC (65731.42 s UT) on 17 March 2002, the HETE FREGATE 
and WXM instruments detected a low fluence GRB that exhibited 
unusually strong spectral evolution. The burst, H1959, was promptly 
reported as a GCN Alert Notice within 34 seconds of the detection 
time. Position resolution and penetration depth in the WXM detectors 
depend on photon energy. The extreme hard-to-soft spectral evolution 
of this burst, quite different from that of a "typical" burst, caused 
an automatic quality check on the location result to fail, so the 
flight location was not transmitted to the GCN. Accurate localization 
of the burst required a "special case" ground-based analysis. A 
preliminary localization was reported as a GCN Position Notice at 53 
min after the burst, and successive refinements were reported as GCN 
Position Notices at 6 hours and 9 hours after the burst. The ground 
analysis produced a location which can be expressed as a circle with 
a 90% confidence radius of 18 arcminutes centered at:

RA = 10h 23m 21s, Dec = +12d 44' 38" (J2000)

This location was reported in a GCN Alert Notice issued at 18 Mar 
2002 03:09:08 UT.

In the FREGATE 8-40 keV band, H1959 had a duration of less than 10 
seconds, with the majority of the counts occurring in an initial hard 
spike with duration ~2s.  A total of 537 net counts were detected, 
corresponding to a fluence of ~1 x 10-7 ergs cm-2 . The peak flux 
averaged over 0.2s was ~7 x 10-8 ergs cm-2 s-1 (ie 2.5 x Crab flux).

Further information (including a light curve) for GRB020317 is 
provided at the following URL:

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

This message is citable.