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GCN Circular 9568

Subject
GRB 090618: Suzaku WAM observation of the prompt emission
Date
2009-06-24T13:05:44Z (15 years ago)
From
Kenta Kono at Miyazaki U <kenta0514@astro.miyazaki-u.ac.jp>
K. Kono, A. Daikyuji, E. Sonoda, N. Ohmori, 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 bright, long GRB 090618 was detected by the Suzaku Wide-band All-sky
Monitor (WAM) which covers an energy range of 50 keV - 5 MeV
at 08:28:25.592 UT (=T0).
The observed light curve shows a multi-peaked structure
starting at T0-5 s and ending at T0+149 s,
with a duration (T90) of about 105 seconds.
The fluence in 100 - 1000 keV was (1.58 $B!^(B 0.07) x10-4 erg/cm2.
The 1-s peak flux measured from T0+65 s was 20.7 (-0.9, +0.8) photons/cm2/s
and 9.83(-0.36, +0.26) x10-5 erg/cm2/s in the same energy range.

Preliminary result shows that the time-averaged spectrum from T0-5 s
to T0+149 s is well fitted by a single power-law with a photon index
of 2.32 $B!^(B 0.04 (chi2/d.o.f = 51/51).
The 1-s peak spectrum is well fitted by a power-law with exponential
cutoff model:
dN/dE ~ E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
alpha: 1.21 $B!^(B 0.13, and
Epeak: 623 (-39, +44) keV (chi2/d.o.f. = 41/50).

Due to the brightness of this burst, a 3% systematic error
was added for low energy channels.
All the quoted errors are at 90% confidence level,

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