TITLE: GCN CIRCULAR NUMBER: 9897 SUBJECT: GRB 090902B: Suzaku WAM observation of the prompt emission DATE: 09/09/05 04:36:48 GMT FROM: Kazutaka Yamaoka at Aoyama Gakuin U Y. Terada, M. Tashiro, A. Endo, K. Onda, T. Sugasahara, W. Iwakiri (Saitama U.), K. Yamaoka, S. Sugita (Aoyama Gakuin U.), M. Ohno, M. Suzuki, M. Kokubun, T. Takahashi (ISAS/JAXA), Y. E. Nakagawa, T. Tamagawa (RIKEN), N. Ohmori, A. Daikyuji, E. Sonoda, K. Kono, H. Hayashi, K. Noda, Y. Nishioka, M. Yamauchi (Univ. of Miyazaki), N. Vasquez (Tokyo Tech.), Y. Urata (NCU), Y. Hanabata, T. Uehara, T. Takahashi, Y. Fukazawa (Hiroshima U.), T. Enoto, K. Nakazawa, K. Makishima (Univ. of Tokyo), S. Hong (Nihon U.), on behalf of the Suzaku WAM team, report The Fermi detected long GRB 090902B (Bissaldi et al., GCN 9866, de Palma et al. GCN 9867) triggered the Suzaku Wide-band All-sky Monitor (WAM) which covers an energy range of 50 keV - 5 MeV at 11:05:08.446 UT (=T0). The observed light curve shows a multi-peaked structure lasting from T0-0.5 s to T0+24.5 s with a duration (T90) of about 19 seconds. The fluence in 100 - 1000 keV was 1.45 (-0.04, +0.03)x10^-4 erg/cm^2. The 1-s peak flux measured from T0+14.5 s was 21.3 (-1.3, +0.9) photons/cm^2/s in the same energy range. Preliminary result shows that the time-averaged spectrum from T0-0.5 s to T0+24.5 s is well fitted by a power-law with exponential cutoff model: dN/dE ~ E^{-alpha} * exp(-(2-alpha)*E/Epeak) with alpha: 0.91 +/- 0.10, and Epeak: 885 (-38, +39) keV (chi^2/d.o.f. = 25.5/24). Due to this GRB brightness, a 3% systematcic error was added for low energy channels. In addition, there might be some calibration uncertainties in fluence because the GRB photons came into the WAM through the base plate of the satellite. All the quoted errors are at 90% confidence level. The light curves for this burst are available at: http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html