Coherent Mechanisms of Pulsar Radio Emission

Relativistic plasma masers operating on the anomalous cyclotronCherenkov resonance ω − k‖v‖ + ωB/ γres = 0 and the Cherenkov-drift resonance ω − k‖v‖ − kxud = 0, are capable of explaining the main observational characteristics of pulsar radio emission. Both electromagnetic instabilities are due to the interaction of the fast particles from the primary beam and from the tail of the secondary pairs distribution with the normal modes of a strongly magnetized one-dimensional electron-positron plasma. In a typical pulsar both resonances occur in the outer parts of magnetosphere at rres ≈ 10 cm. 1. Emission mechanisms We have shown (Lyutikov, Blandford & Machabeli 1999b) that pulsar radiation may be generated by two kinds of electromagnetic plasma instabilities – cyclotron-Cherenkov instability, developing at the anomalous Doppler resonance ω(k)− k‖V‖ + ωB/γres = 0 (1) and Cherenkov-drift instability, developing at the Cherenkov-drift resonance ω(k)− k‖V‖ − kxud = 0 (2) The cyclotron-Cherenkov instability is responsible for the generation of the coretype emission and the Cherenkov-drift instability is responsible for the generation of the cone-type emission. These electromagnetic instabilities are the strongest instabilities in the pulsar magnetosphere (Lyutikov 1999a). Both instabilities are maser-type in a sense that an induced emission dominates over spontaneous. From a classical viewpoint, a random incoming wave forces a particle to emit a wave ”in phase” with initial one, so that the resulting intensity is proportional to N where N is a number of the interfering waves.