GRB 090813: Suzaku WAM observation of the prompt emission
T. Uehara, Y. Hanabata, T. Takahashi, Y. Fukazawa (Hiroshima U.),
Y. Terada, M. Tashiro, A. Endo, K. Onda, T. Sugasahara,
W. Iwakiri (Saitama U.), S. Sugita, K. Yamaoka (Aoyama Gakuin U.),
M. Ohno, M. Suzuki, M. Kokubun, T. Takahashi (ISAS/JAXA),
Y. E. Nakagawa, T. Tamagawa (RIKEN), N. Ohmori, A. Daikyuji,
E. Sonoda, K. Kono, H. Hayashi, K. Noda, Y. Nishioka, M. Yamauchi
(Univ. of Miyazaki), N. Vasquez (Tokyo Tech.), Y. Urata (NCU),
T. Enoto, K. Nakazawa, K. Makishima (Univ. of Tokyo), S. Hong
(Nihon U.), on behalf of the Suzaku WAM team, report
The long, GRB 090813
(Swift/BAT trigger #359884 ; Cummings et al., GCN 9781;
Fermi GBM trigger #271829444 )
triggered the Suzaku Wide-band All-sky Monitor (WAM)
which covers an energy range of 50 keV - 5 MeV at 04:10:43.2 UT (=T0).
The observed light curve shows a double-peaked structure
lasting from T0-0.8s to T0+1.2s followed by a long weak tail seen up
to T0+6.8s with a duration (T90) of about 7.6 seconds.
The fluence in 100 - 1000 keV was 1.70 (-0.51, +0.61) 10^-6 erg/cm^2.
The 1-s peak flux measured from T0-0.2s was 2.77 (-0.40, +0.35)
photons/cm^2/s in the same energy range.
Preliminary result shows that the time-averaged spectrum from T0-0.8s to
T0+6.8s is well fitted by a single power-law with a photon index
of 1.80 (-0.30, +0.40) (chi^2/d.o.f = 7.6/8).
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: