TITLE: GCN CIRCULAR NUMBER: 11988 SUBJECT: GRB 110428A: Suzaku WAM observation of the prompt emission DATE: 11/05/02 10:21:42 GMT FROM: Makoto Tashiro at Saitama U/Swift W. Iwakiri, Y. Terada, M. Tashiro, K. Takahara, T. Yasuda (Saitama U.), T. Uehara, Y. Hanabata, T. Takahashi, Y. Fukazawa (Hiroshima U.), N. Vasquez (Tokyo Tech.) K. Yamaoka (Aoyama Gakuin U.), M. Ohno, M. Kokubun, T. Takahashi (ISAS/JAXA), S. Sugita (Nagoya U.), Y. E. Nakagawa (Waseda U.), N. Ohmori, M. Akiyama, M. Yamauchi (Univ. of Miyazaki), Y. Urata, P. Tsai (NCU), K. Nakazawa, K. Makishima (Univ. of Tokyo), on behalf of the Suzaku WAM team, report: The long bright GRB 110428A localized by Fermi-LAT (Vasileiou et al., GCN 11982) was observed the Suzaku Wide-band All-sky Monitor (WAM) which covers an energy range of 50 keV - 5 MeV at 09:18:30 UT (=T0). The observed light curve shows double-peaked structure starting at T0-2s, ending at T0+10 s with a duration (T90) of about 5 seconds. The fluence in 100 - 1000 keV was 1.31 (-0.43, +2.03) x 10^-5 erg/cm^2. The 1-s peak flux measured from T0+4 s was 9.91 (-0.34, +1.19) photons/cm^2/s in the same energy range. Preliminary result shows that the time-averaged spectrum from T0-2s to T0+10s is well fitted by a power-law with exponential cutoff model : dN/dE ~ E^{-alpha} * exp(-(2-alpha)*E/Epeak) with alpha 1.11 (-0.22, +0.19), and Epeak 195.5 (-14.4, +15.9) keV (chi2/d.o.f. = 15.8/20). All the quoted errors are at statistical 90% confidence level.