[vsnet-grb-info 4640] GRB 070508: Suzaku/WAM observation of the prompt emission

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6396
SUBJECT: GRB 070508: Suzaku/WAM observation of the prompt emission
DATE:    07/05/09 07:19:38 GMT
FROM:    Takeshi Uehara at Hiroshima U  <uehara at hirax7.hepl.hiroshima-u.ac.jp>

T. Uehara, M. Ohno, T. Takahashi, Y. Fukazawa, C. Kira (Hiroshima U.),
T. Enoto, R. Miyawaki, K. Nakawaza, K. Makishima (Univ. of Tokyo),
K. Yamaoka, Y. E. Nakagawa, S. Sugita (Aoyama Gakuin U.),
Y. Urata, K. Onda, M. Suzuki, K. Morigami, N. Kodaka, M. Tashiro (Saitama U.),
M. Suzuki, T. Tamagawa, Y. Terada (RIKEN), S. Hong (Nihon U.),
M. Kokubun, T. Takahashi (ISAS/JAXA), 
E. Sonoda, M.Yamauchi (Univ. of Miyazaki), and Suzaku WAM team report

The bright, long burst, GRB 070508 (Swift/BAT trigger #278854 ; D. Grupe et al., GCN Circ. 6383 ),
was detected at 04:18:21 UT (=T0) by the Suzaku Wide-band All-sky 
Monitor (WAM) which covers an energy range of 50 keV - 5 MeV.
The observed light curve shows multiple peaked structures 
with a duration (T90) of nearly 12 seconds.
The fluence in 100-1000 keV was (3.0+/-0.1) * 10^-5 erg/cm^2.
The 1-s peak flux was 11.6+/-0.5 photons/cm^2/s
in the same energy range.


Preliminary result shows that the time-averaged spectrum from T0-4 to T0+26 s
can be described by a power law with an exponential cutoff model, 
in the 100 keV - 1000 keV range as follows:

dN/dE =  E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
alpha = 0.96 +/- 0.21 and
Epeak = 233 +/- 12 keV (chi^2/d.o.f. = 29/20).
   

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

The WAM light curve of this event is available at
http://www.astro.isas.ac.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html