[vsnet-grb-info 14726] GRB 140320D: Suzaku WAM observation of the prompt emission

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16040
SUBJECT: GRB 140320D: Suzaku WAM observation of the prompt emission 
DATE:    14/03/29 03:42:36 GMT
FROM:    Tetsuya Yasuda at Saitama U  <yasuda at heal.phy.saitama-u.ac.jp>

T. Yasuda, M. Tashiro, Y. Terada, Y. Ishida, H. Ueno, S. Sugimoto
S. Koyama, S. Takeda, T. Nagayoshi (Saitama U.),
M. Yamauchi, N. Ohmori, M. Akiyama, R. Kinoshita (Univ. of Miyazaki),
M. Ohno, K. Takaki, T. Kawano, R. Nakamura, S. Furui, Y. Fukazawa (Hiroshima U.),
K. Yamaoka (Nagoya U.),  S. Sugita (Ehime U.), W. Iwakiri(RIKEN), 
Y. Hanabata (ICRR), Y. E. Nakagawa, M. Kokubun, T. Takahashi (ISAS/JAXA), 
Y. Urata (NCU), K. Nakazawa, K. Makishima (Univ. of Tokyo)
on behalf of the Suzaku WAM team, report:


The bright, long, and IPN localized GRB 140320D 
(Hurley et al., GCN 16023; Golenetskii et al., GCN 16025) 
triggered the Suzaku Wide-band  All-sky Monitor (WAM) which covers an 
energy range of 50 keV - 5 MeV at 20:21:38.309 UT (=T0). 

The observed light curve shows a multi-peaked structure 
lasting from T0-5 s to T0+50 s with a duration (T90) of about 22 seconds. 
The fluence in 100 - 1000 keV was 1.14 (+0.03, -0.04) x10^-4 erg/cm^2. 
The 1-s peak flux measured from T0+17 s was 35.4 (+0.8, -0.9) photons/cm^2/s 
in the same energy range.

Preliminary result shows that the time-averaged spectrum from T0-10.5 s to T0+49.5 s 
is well fitted in 200 keV to 5 MeV by a power-law with exponential cutoff model:
dN/dE ~  E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
alpha       0.99 (+0.12, -0.13), and
Epeak      746 (+33, -31) keV (chi^2/d.o.f. = 72.1/48).

Fitting by a GRB Band model yields the following parameters:
the low-energy photon index alpha: -0.97 (+0.14, -0.13),
the high-energy photon index beta: <-3.62,
and the peak energy Epeak: 742 (+34, -22) keV (chi^2/d.o.f = 71.4/47).

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

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