TITLE: GCN CIRCULAR NUMBER: 14915 SUBJECT: GRB 130609B: Suzaku WAM observation of the prompt emission DATE: 13/06/18 02:17:01 GMT FROM: Masanori Ohno at Hiroshima U K. Takaki, M. Ohno, T. Kawano, R. Nakamura, S. Furui, Y. Fukazawa (Hiroshima U.), M. Tashiro, Y. Terada, T. Yasuda, Y. Ishida, H. Ueno, S. Sugimoto (Saitama U.), K. Yamaoka (Nagoya U.), M. Yamauchi, M. Akiyama, N. Ohmori (Univ. of Miyazaki), S. Sugita (Ehime U.), Y. E. Nakagawa, M. Kokubun, T. Takahashi (ISAS/JAXA), W. Iwakiri(RIKEN), Y. Hanabata (ICRR), Y. Urata (NCU), K. Nakazawa, K. Makishima (Univ. of Tokyo) on behalf of the Suzaku WAM team, report: The long GRB 130609B (Krimm et al., GCN14841) triggered by the Suzaku Wide-band All-sky Monitor (WAM) which covers an energy range of 50 keV - 5 MeV at 21:38:35 UT (=T0). The observed light curve shows a multi-peaked structure starting at T0, ending at T0+30 s with a duration (T90) of about 19.6 seconds. The fluence in 100 - 1000 keV was 3.77 (+0.24/-0.70) x10^-5 erg/cm^2. The 1-s peak flux measured was 7.03 (+0.39/-2.80) photons/cm^2/s in the same energy range. Preliminary result shows that the time-averaged spectrum from T0 to T0+30 s is well fitted by a power-law with exponential cutoff model: dN/dE ~ E^{-alpha} * exp(-(2-alpha)*E/Epeak) with alpha 1.48 (+0.40/-0.41), and Epeak 845 (+179/-147) keV (chi^2/d.o.f. = 15.2/24). Due to the brightness of this burst, a 5% systematic error was added for low energy channels. All the quoted errors are at statistical 90% confidence level. The light curves for this burst will be available at: http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html