TITLE:   GCN CIRCULAR
NUMBER:  25274
SUBJECT: Konus-Wind observation of GRB 190731A
DATE:    19/08/05 15:36:05 GMT
FROM:    Anastasia Tsvetkova at Ioffe Institute  <tsvetkova@mail.ioffe.ru>

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

The long-duration, hard-spectrum, very bright GRB 190731A
(Fermi-LAT detection: Ohno et al., GCN 25244;
CALET Gamma-Ray Burst Monitor detection: Asaoka  et al., GCN 25246;
Fermi GBM detection: Roberts & Meegan, GCN 25248;
IPN Triangulation: Hurley et al., GCN 25250;
AstroSat CZTI detection: Ghumatkar et al., GCN 25258)
triggered Konus-Wind at T0=81504.082 s UT (22:38:24.082).

The burst light curve shows a multi-peaked structure
which starts at ~T0-1.5 s and has a total duration of~22.0 s.
The emission is seen up to ~5 MeV.

As observed by Konus-Wind, the burst
had a fluence of 1.32(-0.08,+0.08)x10^-4 erg/cm2,
and a 64-ms peak energy flux, measured from T0+0.944 s,
of 3.89(-0.46,+0.46)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst
(measured from T0 to T0+23.808 s)
is best fit in the 20 keV - 5 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.69(-0.05,+0.06),
the high energy photon index beta = -2.30(-0.13,+0.11),
the peak energy Ep = 406(-30,+30) keV,
chi2 = 121/98 dof.

The spectrum near the peak count rate
(measured from T0+0.256 to T0+1.536 s)
is best fit in the 20 keV - 20 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.63(-0.07,+0.08),
the high energy photon index beta = -2.69(-0.50,+0.29),
the peak energy Ep = 875(-118,+120) keV,
chi2 = 107/69 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB190731_T81504/

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