  Radio and X-ray emission from compact sources with accretion disks (active
galactic nuclei, pulsars and X-ray binaries) is considered. It is shown that
both radio and X-ray emission from these sources can be interpreted as emission
of a hot ($T \geqslant 3 \times 10^{7}K$) plasma in the inner part of an
accretion disk or in the disk corona. Radio emission is produced by the maser
amplification of thermal radio emission in a hot plasma and corresponds to the
transitions between highly located energy levels (somewhat similarly to the
recombination lines). The X-ray emission is either thermal radiation from dense
filaments or is produced by the coherent inverse Compton scattering of radio
photons in the same dense filaments. The same mechanism, which gives rise to
the maser amplification at radio wavelengths, produces also laser amplification
in optical in X-ray binaries.

Astrophysics