TITLE: GCN CIRCULAR NUMBER: 9314 SUBJECT: GRB 090428B: Suzaku WAM observation of the prompt emission DATE: 09/05/01 05:22:26 GMT FROM: Takeshi Uehara at Hiroshima U T. Uehara, Y. Hanabata, T. Takahashi, Y. Fukazawa(Hiroshima U.), M. Ohno, M. Suzuki, M. Kokubun, T. Takahashi (ISAS/JAXA), K. Kono, E. Sonoda, M. Yamauchi, N. Ohmori, H. Hayashi, K. Noda, A. Daikyuji, Y. Nishioka (Univ. of Miyazaki), W. Iwakiri, M. Tashiro, Y. Terada, A. Endo, K. Onda, T. Sugasahara (Saitama U.), Y. Urata (NCU), T. Enoto, K. Nakazawa, K. Makishima (Univ. of Tokyo), K. Yamaoka, S. Sugita (Aoyama Gakuin U.), Y. E. Nakagawa, T. Tamagawa (RIKEN), S. Hong (Nihon U.), N. Vasquez (Tokyo Tech.), on behalf of the Suzaku WAM team, report: The long GRB 090428B (Fermi/GBM trigger 262617313 / 090428552, Bissaldi et al., GCN 9295) triggered the Suzaku Wide-band All-sky Monitor (WAM) which covers an energy range of 50 keV - 5 MeV at 13:15:12.66 UT (=T0). The observed light curve shows a single FRED-like peak starting at T0-10s, ending at T0+9s, with a duration (T90) of about 19.0 seconds. The fluence in 100 - 1000 keV was 2.6(+0.5/-0.9) X10^-6 erg/cm^2. The 1-s peak flux measured from T0+1s was 1.1 photons/cm^2/s in the same energy range. Preliminary result shows that the time-averaged spectrum from T0-10s to T0+9s is well fitted by a single power-law with a photon index of 2.0 (+0.5/-0.4) (chi^2/d.o.f = 5/7). All the quoted errors are at statistical 90% confidence level, in which the systematic uncertainties are not included. 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