TITLE: GCN CIRCULAR NUMBER: 10363 SUBJECT: GRB 100131A: Suzaku WAM observation of the prompt emission DATE: 10/02/05 06:03:29 GMT FROM: Yusuke Nishioka at Miyazaki U. Y. Nishioka, H. Hayashi, N. Ohmori, A. Daikyuji, E. Sonoda, K. Kono, K. Noda, M. Yamauchi (Univ. of Miyazaki), T. Sugasahara, M. Tashiro, Y. Terada, A. Endo, K. Onda, W. Iwakiri (Saitama U.), S. Sugita (Nagoya U.), K. Yamaoka (Aoyama Gakuin U.), M. Ohno, M. Suzuki, M. Kokubun, T. Takahashi (ISAS/JAXA), Y. E. Nakagawa, T. Tamagawa (RIKEN), N. Vasquez (Tokyo Tech.), Y. Urata, H.M Lin (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 long GRB 100131A (Fermi/GBM trigger #286651859 ; A. Goldstein et al., GCN 10358) triggered the Suzaku Wide-band All-sky Monitor (WAM) which covers an energy range of 50 keV - 5 MeV on 2010-01-31 17:30:58.052 UT (=T0). The observed light curve shows a multi-peaked structure lasting from T0-0.5s to T0+2s, followed by a weaker emission seen up to T0+4s with a duration (T90) of about 3.2 seconds. The fluence in 100 - 1000 keV was 2.72(-0.41, +0.30) x10^-6 erg/cm^2. The 1-s peak flux measured from T0 s was 4.52(-0.80, +0.57) photons/cm^2/s in the same energy range. Preliminary result shows that the time-averaged spectrum from T0-0.5s to T0+5.5s is well fitted by a single power-law with a photon index of 2.62 (-0.37, +0.44) (chi^2/d.o.f = 11.8/13). 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