  The paper proposes a possible mechanism of interaction of microwaves with
superfluid helium that results in an experimentally observed narrow peak of
microwave absorption on the frequencies by the order of the roton frequency.
The obtained microwave photon absorption coefficient depends on the local
equilibrium distribution function which is established due to fast roton-roton
and roton-phonon interactions. With the availability of superfluid flows, the
local equilibrium distribution function depends on their velocity. The critical
velocity of the flows, at which the absorption of microwaves is replaced by
their radiation, is found.
