  Accreting black holes in galactic X-ray sources are surrounded by hot plasma.
The innermost part of these systems is likely a corona with different
temperatures for ions and electrons. In the so-called low-hard state, hot
electrons Comptonize soft X-ray photons from the disk that partially penetrates
the corona, producing emission up to $\sim 150$ keV, well beyond the
expectations for an optically thick disk of maximum temperature $\sim 10^{7}$
K. However, sources such as Cygnus X-1 produce steady emission up to a few MeV,
which is indicative of a non-thermal contribution to the spectral energy
distribution. We study the radiative output produced by the injection of
non-thermal (both electron and proton) particles in a magnetized corona around
a black hole. Energy losses and maximum energies are estimated for all types of
particles in a variety of models, characterized by different kinds of advection
and relativistic proton content. Transport equations are solved for primary and
secondary particles, and spectral energy distributions are determined and
corrected by internal absorption. We show that a local injection of non-thermal
particles can account for the high energy excess observed in some sources, and
we predict the existence of a high-energy bump at energies above 1 TeV, and
typical luminosities of $\sim 10^{33}$ erg s$^{-1}$. High-energy instruments
such as the future Cherenkov Telescope Array (CTA) can be used to probe the
relativistic particle content of the coronae around galactic black holes.
