  We report hard X-ray and gamma-ray observations of the impulsive phase of the
SOL2017-09-06T11:55 X9.3 solar flare. We focus on a high-energy part of the
spectrum, >100 keV, and perform time resolved spectral analysis for a portion
of the impulsive phase, recorded by the Konus-Wind experiment, that displayed
prominent gamma-ray emission. Given a variety of possible emission components
contributing to the gamma-ray emission, we employ a Bayesian inference to build
the most probable fitting model. The analysis confidently revealed
contributions from nuclear deexcitation lines, electron-positron annihilation
line at 511 keV, and a neutron capture line at 2.223 MeV along with two
components of the bremsstrahlung continuum. The revealed time evolution of the
spectral components is particularly interesting. The low-energy bremsstrahlung
continuum shows a soft-hard-soft pattern typical for impulsive flares, while
the high-energy one shows a persistent hardening at the course of the flare.
The neutron capture line emission shows an unusually short time delay relative
to the nuclear deexcitation line component, which implies that the production
of neutrons was significantly reduced soon after the event onset. This in turn
may imply a prominent softening of the accelerated proton spectrum at the
course of the flare, similar to the observed softening of the low-energy
component of the accelerated electrons responsible for the low-energy
bremsstrahlung continuum. We discuss possible physical scenarios, which might
result in the obtained relationships between these gamma-ray components.
