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GCN Circular 9897

GRB 090902B: Suzaku WAM observation of the prompt emission
2009-09-05T04:36:48Z (15 years ago)
Kazutaka Yamaoka at Aoyama Gakuin U <>
Y. Terada, M. Tashiro, A. Endo, K. Onda, T. Sugasahara,
W. Iwakiri (Saitama U.), K. Yamaoka, S. Sugita (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),
Y. Hanabata, T. Uehara, T. Takahashi, Y. Fukazawa (Hiroshima U.),
T. Enoto, K. Nakazawa, K. Makishima (Univ. of Tokyo), S. Hong
(Nihon U.), on behalf of the Suzaku WAM team, report

The Fermi detected long GRB 090902B (Bissaldi et al., GCN 9866, 
 de Palma et al. GCN 9867) triggered the Suzaku Wide-band All-sky 
Monitor (WAM) which covers an energy range of 50 keV - 5 MeV at 
11:05:08.446 UT (=T0). The observed light curve shows a multi-peaked 
structure lasting from T0-0.5 s to T0+24.5 s with a duration (T90) of about 
19 seconds. The fluence in 100 - 1000 keV was 1.45 (-0.04, +0.03)x10^-4 erg/cm^2. 
The 1-s peak flux measured from T0+14.5 s was 21.3 (-1.3, +0.9) photons/cm^2/s
in the same energy range.

Preliminary result shows that the time-averaged spectrum from
T0-0.5 s to T0+24.5 s is well fitted by a power-law with exponential 
cutoff model:
  dN/dE ~  E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
  alpha:      0.91 +/- 0.10, and
  Epeak:      885 (-38, +39) keV (chi^2/d.o.f. = 25.5/24).

Due to this GRB brightness, a 3% systematcic error was 
 added for low energy channels.  In addition, there might be 
  some calibration uncertainties in fluence because the GRB 
  photons came into the WAM through the base plate of the satellite. 
All the quoted errors are at 90% confidence level. 

The light curves for this burst are available at:
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