TITLE:   GCN CIRCULAR
NUMBER:  21447
SUBJECT: Konus-Wind observation of GRB 170808B
DATE:    17/08/10 18:38:28 GMT
FROM:    Anna Kozlova at Ioffe Institute  <ann_kozlova@mail.ioffe.ru>

A.Kozlova, S. Golenetskii, R. Aptekar, D. Frederiks, P. Oleynik,
M. Ulanov, D. Svinkin, A. Tsvetkova, A. Lysenko, and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration, very bright GRB 170808B
(Fermi GBM observation: Veres et al., GCN 21429;
Fermi LAT Detection: Longo et al., GCN 21430)
triggered Konus-Wind at T0=80859.187 s UT (22:27:39.187).

The burst light curve shows a double-peaked structure
which starts at ~T0-2.3 s and has a total duration of ~18.5 s.
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst
had a fluence of 2.20(-0.08,+0.08)x10^-4 erg/cm2,
and a 64-ms peak flux, measured from T0+15.008 s,
of 7.54(-1.02,+1.03)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+23.808 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.92(-0.06,+0.07),
the high energy photon index beta = -2.33(-0.09,+0.07),
the peak energy Ep = 238(-16,+17) keV
(chi2 = 96/98 dof)

The spectrum near the maximum count rate
(measured from T0+14.848 to T0+15.616 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.52(-0.12,+0.13),
the high energy photon index beta = -2.45(-0.13,+0.10),
the peak energy Ep = 282(-26,+29) keV
(chi2 = 80/67 dof)

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170808_T80859/

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