TITLE: GCN CIRCULAR NUMBER: 4116 SUBJECT: GRB051021: A GRB Localized by HETE DATE: 05/10/21 15:14:48 GMT FROM: Carlo Graziani at U.Chicago A. Yoshida, G. Ricker, J-L. Atteia, N. Kawai, D. Lamb, and S. Woosley, on behalf of the HETE Science Team; M. Arimoto, T. Donaghy, E. Fenimore, M. Galassi, C. Graziani, N. Ishikawa, A. Kobayashi, J. Kotoku, M. Maetou, M. Matsuoka, Y. Nakagawa, T. Sakamoto, R. Sato, T. Shimokawabe, Y. Shirasaki, S. Sugita, M. Suzuki, T. Tamagawa, and K. Tanaka, 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 HETE FREGATE, WXM, and SXC instruments detected GRB 051021 (=H3947) at 13:21:57 UT (48117 SOD) on 21 October 2005. The WXM flight localization was first reported in a GCN Notice issued at 13:22:11 UT, which was 14s after the burst trigger. Ground analysis of the WXM data produced a refined WXM localization that was issued in a GCN Notice at 14:25:34 UT. This ground WXM localization can be expressed as a circle of 7.5 arcminutes radius (90% confidence), centered at R.A. = 01h 56m 24s ; Dec. = +09d 07' 05" (J2000). The SXC detected this event in its Y camera. Ground analysis of the SXC data therefore produced a 1-dimensional location. The intersection of this location with the WXM ground location was issued in a GCN Notice at 14:59:49 UT. This location can be expressed as a box with corners: R.A. = 01h 56m 01.92s ; Dec. = +09d 02' 02.4" R.A. = 01h 56m 54.00s ; Dec. = +09d 05' 16.4" R.A. = 01h 56m 54.72s ; Dec. = +09d 07' 22.8" R.A. = 01h 59m 57.12s ; Dec. = +09d 03' 46.8" (J2000). Further analysis is in progress.