GCN Circular 9951
Subject
GRB 090926A: Suzaku WAM observation of the prompt emission
Date
2009-09-27T14:52:07Z (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 very bright, Fermi-LAT detected GRB 090926A (Fermi-GBM trigger
#275631628/ 090926181; Bissaldi, GCN 9933; Uehara et al., GCN 9934)
triggered the Suzaku Wide-band All-sky Monitor (WAM)
which covers an energy range of 50 keV - 5 MeV at 04:20:27.168 UT (=T0).
The observed light curve shows a multi-peaked structure, lasting from
T0-0.5 s to T0+16.5 s, followed by a weak tail seen up to ~T0+34.5s.
The total duration (T90) was about 13 s and the fluence in
100 - 1000 keV was 9.71(-0.40, +0.22)x 10-5 erg/cm2.
The 1-s peak flux measured from T0+3.5 s was 30.6(-2.3, +1.6) photons/cm2/s
in the same energy range.
Preliminary result shows that the time-averaged spectrum from
T0-0.5 s to T0+34.5 s is well fitted by a GRB Band model as follows.
the low-energy photon index alpha: -1.09 (-0.27, +0.37),
the high-energy photon index beta: -2.63 (-0.17, +0.11),
and the peak energy Epeak: 434 (-30, +32) keV (chi2/d.o.f = 29.7/23).
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 now available at:
http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html