[vsnet-grb-info 8377] GRB 090831A: Suzaku WAM observation of the prompt emission

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9900
SUBJECT: GRB 090831A: Suzaku WAM observation of the prompt emission
DATE:    09/09/05 07:59:58 GMT
FROM:    Norisuke Ohmori at Miyazaki U  <ohmori at astro.miyazaki-u.ac.jp>

N. Ohmori, K. Noda, E. Sonoda, K. Kono, H. Hayashi, A. Daikyuji, 
Y. Nishioka, M. Yamauchi (Univ. of Miyazaki),
M. Ohno, M. Suzuki, M. Kokubun, T. Takahashi (ISAS/JAXA),
K. Yamaoka, S. Sugita (Aoyama Gakuin U.), Y. E. Nakagawa,
T. Tamagawa (RIKEN), S. Hong (Nihon U.), N. Vasquez (Tokyo Tech.),
Y. Hanabata, T. Uehara, T. Takahashi, Y. Fukazawa (Hiroshima U.),
W. Iwakiri, M. Tashiro, Y. Terada, A. Endo, K. Onda,
T. Sugasahara (Saitama U.), Y. Urata (NCU),
T. Enoto, K. Nakazawa, K. Makishima (Univ. of Tokyo),
on behalf of the Suzaku WAM team, report:

The long GRB 090831A (Fermi-GBM trigger 273396998 / 090831317;
Arne et al., GCN 9850, MAXI-GSC; Matsuoka et al., GCN 9852) 
triggered the Suzaku Wide-band All-sky 
Monitor (WAM) which covers an energy range of 50 keV - 5 MeV
at 07:36:36.472 UT (=T0).

The observed light curve shows main three peaks starting at T0s, 
ending at T0+10s, followed by a long weak tail seen up to T0+48s.
The total T90 duration is about 53 seconds.

The fluence in 100 - 1000 keV was 6.8 (-1.8, +1.0)x10-6 erg/cm2.
The 1-s peak flux measured from T0+4 s was 1.8 (-0.2, +0.3) photons/cm2/s 
in the same energy range.

Preliminary result shows that the time-averaged spectrum from
T0 s to T0+48 s is well fitted by a power-law with exponential cutoff model:
  dN/dE ~  E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
  alpha        0.89(-0.91, +0.65), and
  Epeak        286(-57, +88) keV (chi2/d.o.f. = 93/80).
 
All the quoted errors are at statistical 90% confidence level,
in which the systematic uncertainties are not included.
 
The light curves for this burst is available at:
http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html