TITLE: GCN CIRCULAR NUMBER: 9186 SUBJECT: GRB 090418B: Suzaku WAM observation of the prompt emission DATE: 09/04/22 09:12:55 GMT FROM: Kenta Kono at Miyazaki U K. Kono, E. Sonoda, M. Yamauchi, N. Ohmori, H. Hayashi, K. Noda, A. Daikyuji, Y. Nishioka (Univ. of Miyazaki), M. Ohno, M. Suzuki, M. Kokubun, T. Takahashi (ISAS/JAXA), 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), T. Uehara, T. Takahashi, Y. Fukazawa, Y. Hanabata (Hiroshima U.), S. Hong (Nihon U.), N. Vasquez (Tokyo Tech.), on behalf of the Suzaku WAM team, report: The long GRB 090418B was detected by the Suzaku Wide-band All-sky Monitor (WAM) which covers an energy range of 50 keV - 5 MeV at 08:54:21.299 UT (=T0). The observed light curve shows a multi-peaked structure starting at T0-3 s, ending at T0+35 s, with a duration (T90) of about 29 seconds. The fluence in 100 - 1000 keV was 1.22 (-0.14, +0.06) x10-5 erg/cm2. The 1-s peak flux measured from T0+32 s was 2.13 (-0.58, +0.35) photons/cm2/s in the same energy range. Preliminary result shows that the time-averaged spectrum from T0+14 s to T0+52 s is well fitted by a single power-law with a photon index of 2.09 (-0.20, +0.22) (chi2/d.o.f = 13/17). All the quoted errors are at statistical 90% confidence level, in which the systematic uncertainties are not included. The light curves for this burst will be available at: http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/untrig/grb_table.html