Coherent Emission Mechanisms in Radio Pulsars

Abstract

A theory of pulsar radio emission generation, in which the observed waves are produced directly by the maser-type plasma instabilities on the anomalous cyclotron-Cherenkov resonance $$\omega - \kappa _{ \shortparallel \nu \shortparallel } + \omega _B /\gamma _{res} = 0$$ and the Cherenkov-drift resonance $$\omega - \kappa _{ \shortparallel \nu \shortparallel } - \kappa _x \upsilon _d = 0$$ , is capable of explaining the main observational characteristics of pulsar radio emission. The instabilities are due to the interaction of the fast particles of the primary beam and from the tail of the distribution with the normal modes of a strongly magnetized one-dimensional electron-positron plasma. The waves emitted at these resonances are vacuum-like electromagnetic waves that may leave the magnetosphere directly. The cyclotron-Cherenkov instability is responsible for core emission pattern and the Cherenkov-drift instability produces conal emission. The conditions for the development of the cyclotron-Cherenkov instability are satisfied for the both typical and millisecond pulsars provided that the streaming energy of the bulk plasma is not very high γ p = 5 ÷ 10. In a typical pulsar the cyclotron-Cherenkov and Cherenkov-drift resonances occur in the outer parts of magnetosphere at r res ≈ 109cm. This theory can account for various aspects of pulsar phenomenology including the morphology of the pulses, their polarization properties and spectral behavior.