GCN Circular 9787

S. Golenetskii, R.Aptekar, D. Frederiks, E. Mazets, V. Pal'shin,
P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline
on behalf of the Konus-Wind team, report:

GRB 090813 (Swift trigger=359884: Cummings et al., GCN 9781
Not found
 
 
)
triggered Konus-Wind at T0=15041.925 s UT (04:10:41.925)

The burst started with a double-peaked structure with a
duration of ~2 s.
Another, softer peak, with a duration of ~1.5 s,
was observed at T0 + 6s.

The Konus-Wind light curves of this GRB are available at
http://www.ioffe.ru/LEA/GRBs/GRB090813_T15041/

As observed by Konus-Wind the burst had
a fluence of 2.4(-0.4,+0.5)x10-6 erg/cm2, and
a 64-ms peak flux, measured from T0,
of 3.3(-0.6,+0.7)x10-6 erg/cm2/s
(both in the 20 keV - 1 MeV energy range).

The time-integrated spectrum of the burst (from T0 to T0+8.448 s)
is well fitted (in the 20 keV - 1 MeV range)
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -1.37(-0.28,+0.35),
and Ep = 104(-23,+41)keV (chi2 = 58/61 dof).

Fitting by GRB (Band) model yields to the same alpha and Ep values
with the high energy photon index beta < -9.

The spectrum at the maximum count rate, measured from T0 to T0+0.256 s,
is well fitted (in the 20 keV - 1 MeV range)
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.85(-0.29,+0.34),
and Ep = 195(-43,+71)keV (chi2 = 20/23 dof).

All the quoted values are preliminary.
All the quoted errors are at the 90% confidence level.