GCN Circular 1102

GRB010923(=H1764): A Short Duration GRB Detected by HETE

G. Ricker, D. Lamb, and S. Woosley on behalf of the HETE Science Team;

R. Vanderspek, G. Crew, J. Doty, G. Monnelly, J. Villasenor, 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;

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

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

write:

The HETE Fregate instrument has detected an unusual short (<1 sec), 
bright (>12 sigma) GRB that was reported promptly in a GCN Notice as 
H1764. The burst occurred at 33869.82 SOD {09:24:29.82} UT on 23 
September. The burst was not seen in the WXM nor in the SXC 
instruments. The burst therefore apparently occurred outside the 
fields-of-view of the WXM and the SXC, and thus no localization was 
possible. Localization of this burst may be possible through 
triangulation between HETE and the IPN.

The light curve for GRB010923 at high energies is characterized by a 
very narrow, double-peaked emission core, ~350 ms in duration. Each 
of the two peaks in the core is ~50 ms in duration. In the 32-400 keV 
band, a total of 284 counts were detected during 940 ms, with 50 per 
cent of the detected counts occurring in 200 ms. In the 8-40 keV 
band, an exponential tail extends for ~2 s. A total of 268 counts 
were detected during that interval, corresponding to a fluence of ~5 
x 10-8 ergs cm-2. The peak flux was >1 x 10-7 ergs cm-2 s-1 (i.e., >4 
x Crab flux).

Searches for this unusual event are encouraged with other instruments 
and at other energies.