[vsnet-grb-info 8030] GRB 090617: Suzaku WAM observation of the prompt emission

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9569
SUBJECT: GRB 090617: Suzaku WAM observation of the prompt emission
DATE:    09/06/24 15:14:32 GMT
FROM:    Norisuke Ohmori at Miyazaki U  <ohmori at astro.miyazaki-u.ac.jp>

N. Ohmori, A. Daikyuji, E. Sonoda, K. Kono, H. Hayashi, K. Noda,  
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 short GRB 090617 (Fermi-GBM trigger 266907600 / 090617208;
Bissaldi et al., GCN 9523) triggered the Suzaku Wide-band All-sky 
Monitor (WAM) which covers an energy range of 50 keV - 5 MeV
at 04:59:58.105 UT (=T0).

The observed light curve shows a bright multi-peaked structure
starting at T0+0.45 s, ending at T0+0.6 s. 
The total T90 duration is about 0.14 seconds.

The fluence in 100 - 1000 keV was 8.8 (-5.9, +2.8)x10-7 erg/cm2.
The 1-s peak flux measured from T0 s was 1.7 (-1.0, +0.5) photons/cm2/s 
in the same energy range.

Preliminary result shows that the time-averaged spectrum from
T0 s to T0+1 s is well fitted by a power-law with exponential cutoff model:
  dN/dE ~  E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
  alpha       -0.02(-1.21, +1.07), and
  Epeak        698(+859, -171) keV (chi2/d.o.f. = 13.7/13).
 
All the quoted errors are at statistical 90% confidence level,
in which the systematic uncertainties are not included.
 
The light curves for this burst is available at:
http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html