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GCN Circular 9992

Subject

GRB 090929A: Suzaku WAM observation of the prompt emission

Date

2009-10-05T08:59:49Z (15 years ago)

From

Norisuke Ohmori at Miyazaki U <ohmori@astro.miyazaki-u.ac.jp>

N. Ohmori, E. Sonoda, K. Kono, H. Hayashi, A. Daikyuji, 
Y. Nishioka, K. Noda, 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 090929A (Fermi-GBM trigger 275891585  / 090929190;
Arne Rau et al., GCN9962Loading...
 
 ) triggered the Suzaku Wide-band All-sky 
Monitor (WAM) which covers an energy range of 50 keV - 5 MeV
at 04:33:04.634 UT (=T0).

The observed light curve shows a bright multi-peaked structure
starting at T0-1 s, ending at T0+5 s. 
The total T90 duration is about 3.8 seconds.

The fluence in 100 - 1000 keV was 4.96 (-4.47, +5.32) x10-6 erg/cm2.
The 1-s peak flux measured from T0-0.5s was 5.59 (-0.68, +0.53)
photons/cm2/s in the same energy range.
The incident angle for this burst is not good, so the fluence 
and peak flux might have large systematic uncertainties.

Preliminary result shows that the time-averaged spectrum from
T0-1s to T0+5s is well fitted by a power-law with exponential cutoff model:
  dN/dE ~  E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
  alpha       0.86(-0.80, +0.36), and
  Epeak        557(-98, +117) keV (chi2/d.o.f. = 125/98).

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