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GCN Circular 9816

Subject
GRB 090812: Suzaku WAM observation of the prompt emission
Date
2009-08-17T09:36:54Z (15 years ago)
From
Kazuhiro Noda at Miyazaki U <kaz1206@astro.miyazaki-u.ac.jp>
K. Noda, E. Sonoda, N. Ohmori, K. Kono, H. Hayashi,
A. Daikyuji, Y. Nishioka, M. Yamauchi (Univ. of Miyazaki),
Y. Hanabata, T. Uehara, T. Takahashi, Y. Fukazawa (Hiroshima U.),
M. Ohno, M. Suzuki, M. Kokubun, T. Takahashi (ISAS/JAXA),
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),
K. Yamaoka, S. Sugita (Aoyama Gakuin U.), Y. E. Nakagawa,
T. Tamagawa (RIKEN), S. Hong (Nihon U.), N. Vasquez (Tokyo Tech.),
on behalf of the Suzaku WAM team, report:

The long GRB 090812 (Swift/BAT trigger #359711; 
Stamatikos et al., GCN 9768; Baumgartner et al., GCN 9775) 
triggered the Suzaku Wide-band  All-sky Monitor (WAM) which covers an 
energy range of 50 keV - 5 MeV at 2009-08-12 06:02:33.68 UT (=T0). 

The observed light curve shows a double-peaked structure, starting at 
T0-30 s and ending at T0+40 s, with a total duration (T90) of about 36 s. 
The fluence in 100 - 1000 keV was 1.50(-0.46, +0.40) x10-6 erg/cm2.
The 1-s peak flux measured from T0+2 s was 2.77(-0.35, +0.23) photons/cm2/s 
in the same energy range.

Preliminary result shows that the time-averaged spectrum from
T0-30 s to T0+40s is well fitted by a power-law with exponential cutoff model:
  dN/dE ~  E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
  alpha:     1.31(-1.09, +0.81), and
  Epeak:     340(-138, +254) keV (chi2/d.o.f. = 36.6/37).

All the quoted errors are at statistical 90% confidence level,
in which the systematic uncertainties are not included.

The light curves for this burst will be available at:
http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html
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