Scattering of Low-Frequency Radiation by a Gyrating Electron

The scattering of electromagnetic radiation by the particle gyrating in an external magnetic field is considered. Particular attention is paid to the low-frequency case, when the frequencies of incident radiation are much less than the electron gyrofrequency. The spectral and polarization features of the scattering cross-section are analyzed in detail. It is found that the scattering transfers the low-frequency photons to high harmonics of the gyrofrequency, into the range of the synchrotron emission of the electron. The total scattering cross-section appears much larger than that for the particle at rest. The problem studied is directly applicable to the radio wave scattering in the magnetosphere of a pulsar. The particles acquire relativistic rotational energies as a result of resonant absorption of the high-frequency radio waves and concurrently scatter the low-frequency radio waves, which are still below the resonance. It is shown that the scattering can affect the radio intensity and polarization at the lowest frequencies and can compete with the resonant absorption in contributing to the low-frequency turnover in the pulsar spectrum. Moreover, the scattering can be an efficient mechanism of the pulsar high-energy emission, in addition to the synchrotron re-emission of the particles. Other astrophysical applications of the scattering by gyrating particles are pointed out as well.