TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3402 SUBJECT: GRB050509c (=H3751): An X-Ray Flash Localized By HETE DATE: 05/05/10 03:51:45 GMT FROM: Don Lamb at U.Chicago GRB050509c (=H3751): An X-Ray Flash Localized By HETE G. Prigozhin, 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, J. Kotoku, M. Maetou, M. Matsuoka, Y. Nakagawa, T. Sakamoto, R. Sato, Y. Shirasaki, M. Suzuki, T. Tamagawa, K. Tanaka, Y. Yamamoto, and A. Yoshida, on behalf of the HETE WXM Team; N. Butler, G. Crew, J. Doty, 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 050509c at 22:45:54 UT (81953.95 SOD) on 9 May 2005. This was a weak burst consisting of a single pulse ~25 s long, with almost no emission above 18 keV in the WXM. The WXM flight localization can be expressed as a circle of radius 14 arcminutes (90% confidence) that is centered at WXM-Flight: RA = 12h 52m 39s, Dec =-44d 17' 50" (J2000). The first flight localization was distributed in a GCN Notice issued at 22:46:13 UT, 19 s after the burst trigger. Ground analysis of the WXM data produced a refined WXM localization that was in a GCN Notice issued 10 May 05 at 00:43:29 UT. This ground WXM localization can be expressed as a rectangle with corners: R.A. = 12 52 15.4 ; Dec. = -44 23 06 R.A. = 12 54 05.0 ; Dec. = -44 23 46 R.A. = 12 54 01.7 ; Dec. = -45 10 01 R.A. = 12 52 11.3 ; Dec. = -45 09 18 (J2000). The burst was also detected by the SXC Y camera. Ground analysis of the SXC data produced a long thin rectangle. Truncating the rectangle by the WXM ground localization results in a rectangle with corners: R.A. = 12 54 02.9 ; Dec. = -44 52 23 R.A. = 12 52 12.7 ; Dec. = -44 51 43 R.A. = 12 52 13.2 ; Dec. = -44 48 43 R.A. = 12 54 03.1 ; Dec. = -44 49 23 (J2000). A preliminary spectral analysis indicates that Epk < 19 keV. The preliminary fluences are: S(2-30 keV) = 6E-07 erg cm^-2, S(30-400) = 3E-07 erg cm^-2. Therefore GRB 050509c is an X-ray flash. A light curve, skymap, and spectral information for GRB 050509c are provided at the following URL: http://space.mit.edu/HETE/Bursts/GRB050509C/