TITLE: GCN CIRCULAR NUMBER: 2701 SUBJECT: GRB040912 (= H3557): A Long GRB or XRF Localized by HETE DATE: 04/09/12 23:14:09 GMT FROM: George Ricker at MIT GRB040912 (= H3557): A Long GRB or XRF Localized by HETE N. Butler, G. Ricker, J-L. Atteia, N. Kawai, D. Lamb, and S. Woosley, on behalf of the HETE Science Team; T. Donaghy, E. Fenimore, M. Galassi, C. Graziani, M. Matsuoka, Y. Nakagawa, T. Sakamoto, R. Sato, Y. Shirasaki, M. Suzuki, T. Tamagawa, Y. Urata, T. Yamazaki, Y. Yamamoto, and A. Yoshida, on behalf of the HETE WXM Team; G. Crew, J. Doty, A. Dullighan, 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; C. Barraud, M. Boer, J-F Olive, J-P Dezalay, and K. Hurley, on behalf of the HETE FREGATE Team; report: At 14:12:17 UT (13260 SOD) on 12 September 2004, the Fregate and WXM instruments on HETE detected GRB040912 (= H3557), an unusual, long X-ray rich GRB or XRF. The burst has been localized to a circle of 7' radius centered on RA = 23h 56m 54s, Dec = -1d 00' 02" (J2000) The burst duration is ~20 seconds in the 7-30 keV band, but the 2-10 keV emission extends for ~150s. Preliminary analyses of the first 40 seconds of burst data show the burst to have Epeak of 58 keV, a 2-30 keV fluence of 7e-7 erg/cms and a 30-400 keV fluence of 4e-7 erg/cm2. While this analysis shows the burst to be an X-ray rich GRB, we expect the ratio of 2-30/30-400 keV fluence to increase once the analysis of the entire burst is complete, at which time H3557 may be re-classified as an XRF. We anticipate providing additional spectral information from this unusual event in a subsequent GCN Circular. This message may be cited.