[vsnet-grb-info 7371] GRB 090227A: Suzaku WAM observation of the prompt emission

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8935
SUBJECT: GRB 090227A: Suzaku WAM observation of the prompt emission
DATE:    09/03/05 14:12:32 GMT
FROM:    Yoshitaka Hanabata at Hiroshima U  <hanabata at hep01.hepl.hiroshima-u.ac.jp>

Y. Hanabata, Y. Fukazawa, T. Takahashi, T. Uehara, C. Kira (Hiroshima U.),
Y. Terada, M. Tashiro, Y. Urata, A. Endo, K. Onda, N. Kodaka,
K. Morigami, T. Sugasahara, W. Iwakiri (Saitama U.), M. Ohno,
M. Kokubun, M. Suzuki, T. Takahashi (ISAS/JAXA), K. Yamaoka,
S. Sugita (Aoyama Gakuin U.), T. Enoto, K. Nakazawa, K. Makishima 
(Univ. of Tokyo), Y. E. Nakagawa, T. Tamagawa (RIKEN),
E. Sonoda, M. Yamauchi, H. Tanaka, R. Hara, N. Ohmori, K. Kono,
H. Hayashi (Univ. of Miyazaki), S. Hong (Nihon U.),
N. Vasquez (Tokyo Tech), on behalf of the Suzaku WAM team, report:

The long GRB 090227A (Bissaldi et al., GCN 8917) triggered the
Suzaku Wide-band All-sky Monitor (WAM) which covers an energy
range of 50 keV - 5 MeV at 07:25:56.862 UT (=T0).

The observed light curve shows a multi-peaked structure starting at T0-1s,
ending at T0+17s with a duration (T90) of about 12.7 seconds. The
fluence in 100 - 1000 keV was 8.00(-1.41, +0.36) x 10^-6 erg/cm^2. The
1-s peak flux measured from T0+1s was 2.27(-1.00, +0.14)
photons/cm^2/s in the same energy range.

Preliminary result shows that the time-averaged spectrum from T0-1s
to T0+17s is fitted by a power-law with exponential cutoff model:

 dN/dE ~  E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
 alpha       1.16(-0.28, +0.22), and
 Epeak       1328(-465, +951) keV (chi^2/d.o.f. = 6.73/14).

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

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