[vsnet-grb-info 7716] GRB 090424: Suzaku WAM observation of the prompt emission

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9270
SUBJECT: GRB 090424: Suzaku WAM observation of the prompt emission 
DATE:    09/04/27 14:14:03 GMT
FROM:    Yoshitaka Hanabata at Hiroshima U  <hanabata at hep01.hepl.hiroshima-u.ac.jp>

Y. Hanabata, T. Uehara, T. Takahashi, Y. Fukazawa(Hiroshima U.),
K. Kono, E. Sonoda, M. Yamauchi, N. Ohmori, H. Hayashi,
K. Noda, A. Daikyuji, Y. Nishioka (Univ. of Miyazaki),
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 090424 (Swift/BAT trigger #350311 ; Cannizzo et al., GCN
9223) triggered the Suzaku Wide-band All-sky Monitor (WAM) which
covers an energy range of 50 keV - 5 MeV at 14:12:09.216 UT (=T0).
The observed light curve shows a multi-peaked structure starting at
T0-1 s, ending at T0+12 s, with a duration (T90) of about 4.18
seconds.

The fluence in 100 - 1000 keV was 1.36 (-0.10, +0.28) x10^-5 erg/cm2.
The 1-s peak flux measured from T0 was 12.6 (-0.9, +1.6) photons/cm2/s
in the same energy range.

Preliminary result shows that the time-averaged spectrum from T0-1 s
to T0+12 s is fitted by a power-law with exponential cutoff model:

 dN/dE ~  E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
 alpha       0.92 (-0.77, +0.66), and
 Epeak       250 (-83, +41) keV (chi^2/d.o.f. = 18.9/27).

Due to the high counting rate of this GRB, a 3% systematic error
was added for low energy channels.
We note that this GRB came from the WAM 2 direction,
which has a large uncertainty ~40 % in the absolute flux.


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