TITLE:   GCN CIRCULAR
NUMBER:  9701
SUBJECT: Konus-Wind observations of bright hard GRB 090720B
DATE:    09/07/23 10:06:08 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred@mail.ioffe.ru>

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 090720B (Fermi/GBM trigger 269802178/090720710: Burgess et al., GCN 9698;
IPN localization box: Golenetskii et al., GCN 9700)
triggered Konus-Wind at T0=61379.486 s UT (17:02:59.486).

This bright hard GRB started with a series of several short spikes,
followed by a smoother structure. The emission is seen above 10 MeV
for the whole duration of the event (~16 s).
The Konus-Wind light curves of this GRB are available at
http://www.ioffe.ru/LEA/GRBs/GRB090720_T61379/

As observed by Konus-Wind the burst had a fluence
of 1.8(-0.5,+0.7)x10-5 erg/cm2, and
a 2-ms peak flux, measured from T0+0.186 s,
of 8.3(-2.8,+4.1)x10-5 erg/cm2/s
(both in the 20 keV - 15 MeV energy range).

The time-integrated spectrum of the burst, measured from T0 to T0+16.640 s,
is well fit (in the 20 keV - 15 MeV range)
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep), with
alpha = -1.16(-0.13,+0.17), and
Ep = 1370(-580,+1190)keV (chi2 = 99/98 dof).

The spectrum at the maximum count rate, measured from T0+0.128 to T0+0.192 s,
is also well fit (in the 20 keV - 15 MeV range) by a power law with
exponential cutoff model, for which:
alpha = -0.47(-0.42,+0.71), and
Ep = 710(-280,+590)keV (chi2 = 7.3/8 dof).

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