  The pickup protons originate as a result of the ionization of hydrogen atoms
in the supersonic solar wind, forming the suprathermal component of protons in
the heliosphere. While picked by the heliospheric magnetic field and convected
into the heliosheath, the pickup protons may suffer the stochastic acceleration
by the solar wind turbulence in the region from the Sun up to the heliospheric
termination shock, where they can also experience the shock-drift acceleration
or the reflection from the cross-shock potential. These processes create a
high-energy "tail" in the pickup ion energy distribution. The properties of
this energetic pickup proton population are still not well-defined, despite
they are vital for the models to simulate energetic neutral atom fluxes. We
have considered two scenarios for pickup proton velocity distribution
downstream of the heliospheric termination shock (filled shell with energetic
power-law "tail" and bi-Maxwellian). Based on the numerical kinetic model and
observations of the energetic neutral atom fluxes from the inner heliosheath by
the IBEX-Hi instrument, we have characterized the pickup proton distribution
and provided estimations on the properties of the energetic pickup proton
population downstream of the termination shock.
