TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1102 SUBJECT: GRB010923(=H1764): A Short Duration GRB Detected by HETE DATE: 01/09/23 16:00:28 GMT FROM: George Ricker at MIT 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.