  Context. Many low-redshift active galactic nuclei harbor a supermassive black
hole accreting matter at low or medium rates. At such rates, the accretion flow
usually consists of a cold optically thick disk, plus a hot, low density,
collisionless corona. In the latter component, charged particles can be
accelerated to high energies by various mechanisms. Aims. We aim to
investigate, in detail, nonthermal processes in hot accretion flows onto
supermassive black holes, covering a wide range of accretion rates and
luminosities. Methods. We developed a model consisting of a thin
Shakura-Sunyaev disk plus an inner hot accretion flow or corona, modeled as a
radiatively inefficient accretion flow, where nonthermal processes take place.
We solved the transport equations for relativistic particles and estimated the
spectral energy distributions resulting from nonthermal interactions between
the various particle species and the fields in the source. Results. We covered
a variety of scenarios, from low accretion rates up to 10% of the Eddington
limit, and identified the relevant cooling mechanisms in each case. The
presence of hadrons in the hot flow is decisive for the spectral shape, giving
rise to secondary particles and gamma-ray cascades. We applied our model to the
source IC 4329A, confirming earlier results that showed evidence of nonthermal
particles in the corona.
