TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4124 SUBJECT: GRB051021 (=H3947): Refined Analysis DATE: 05/10/21 20:57:21 GMT FROM: Carlo Graziani at U.Chicago J-F Olive, 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, K. Tanaka, 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-P Dezalay, and K. Hurley, on behalf of the HETE FREGATE Team; report: We have analyzed the full FREGATE+WXM data for HETE trigger H3934 (GRB051021.56). The 30-400 keV light curve has two sharp peaks, separated by about 10 s, superposed on a gentler rise-and-fall. The burst had a T90 duration of 38s in the 7-40 keV band, and of 27s in the 30-400 keV band. Emission in the 2-25 keV band appears to continue for at least 90s post-trigger, mostly below 10 keV. The integrated spectrum is well-fit by a cutoff power-law function. The best-fit parameters are: alpha = -1.16 --- 90% confidence interval is [-1.25 -1.06] Epeak = 94.2 --- 90% confidence interval is [76.7 , 111.7] The 2-30 keV fluence is 3x10^-6 erg/cm2, while the 30-400 keV fluence is 6 x 10^-6 keV. Since the ratio S(2-30)/S(30-400) is 0.41, this event is classified as an X-Ray Rich GRB. The pseudo-redshift estimated for this burst is pz = 1.4. A light curve, a skymap, and spectral information for this event are provided at the following URL: http://space.mit.edu/HETE/Bursts/GRB051021