  The high-energy emission mechanisms based on the radio photon reprocessing by
the ultrarelativistic plasma particles in the open field line tube of a pulsar
are considered. The particles are believed to acquire relativistic gyration
energies as a result of resonant absorption of pulsar radio emission. The
spontaneous synchrotron re-emission of these particles falls into the optical
and soft X-ray ranges and can at least partially account for the pulsar
non-thermal high-energy emission. Besides that, the radio photons, which are
still below the resonance, can be deposited into the high-energy range by means
of the scattering off the gyrating particles. This process can also markedly
contribute to the pulsar high-energy emission and underlie the potentially
observable features of the radio -- high-energy connection. Based on the theory
developed, we interpret the manifestations of the radio -- high-energy
connection already observed in the Crab and Vela pulsars. Furthermore, it is
shown that generally the most prominent connection is expected at the lowest
radio frequencies, beyond the low-frequency turnover of a pulsar.
