Y. Hanabata, Y. Fukazawa, T. Takahashi, T. Uehara, C. Kira (Hiroshima U.),
Y. Terada, M. Tashiro, Y. Urata, A. Endo, K. Onda, N. Kodaka,
K. Morigami, T. Sugasahara, W. Iwakiri (Saitama U.), M. Ohno,
M. Kokubun, M. Suzuki, T. Takahashi (ISAS/JAXA), K. Yamaoka,
S. Sugita (Aoyama Gakuin U.), T. Enoto, K. Nakazawa, K. Makishima
(Univ. of Tokyo), Y.E. Nakagawa, T. Tamagawa (RIKEN),
E. Sonoda, M. Yamauchi, H. Tanaka, R. Hara, N. Ohmori, K. Kono,
H. Hayashi (Univ. of Miyazaki), S. Hong (Nihon U.),
N. Vasquez (Tokyo Tech), on behalf of the Suzaku WAM team, report:
The long GRB 090131 (Goldstein et al., GCN 8876) triggered the
Suzaku Wide-band All-sky Monitor (WAM) which covers an energy
range of 50 keV - 5 MeV at 2009-01-31 02:09:24.187 UT (=T0).
The observed light curve shows a multi-peaked structure starting at T0-5s,
ending at T0+46s with a duration (T90) of about 32.6 seconds. The fluence in
100 - 1000 keV was 9.95(-0.59, +0.57) x 10^-6 erg/cm^2. The 1-s peak
flux measured from T0+19s was 5.01(-0.39, +0.35) photons/cm^2/s in the
same energy range.
Preliminary result shows that the time-averaged spectrum from T0-5s
to T0+46s is fitted by a single power-law with a photon index
of 2.29(-0.15, +0.17) (chi^2/d.o.f = 11.4/13).
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: