Pulsar Eclipses due to Induced Scattering in Magnetized Plasmas

Abstract

Induced scattering due to three-wave interactions in a magnetized plasma is proposed as a possible mechanism for pulsar eclipses. The highly beamed, intense radio emission from a pulsar car1 induce instability of low-frequency waves in the plasma of the companion wind. When a sufficient level of the low-frequency waves is built up, the photon beam is scattered by these waves, resulting in a pulsar eclipse. The scattering is considered in two regimes: small-angle scattering, in which the wavenumber of the low-frequency waves is much smaller than those of the high-frequency photons, and large-angle scattering, in which the wavenumbers of the three waves are comparable. For small-angle scattering, low-frequency z-mode waves are important, and for large-angle scattering, Bernstein waves are important. Both small-angle and large-angle scattering can result in pulsar eclipse, but large-angle scattering (or back-scattering) by Bernstein waves appears the more favored for a complete (continuum) or partial eclipse such as observed for PSR 1957+20 or PSR 1744-24A. In the case of PSR 1744- 24A, the frequency dependence of the eclipse radius estimated for three-wave scattering involving Berstein waves appears more consistent with the observations than for the theory involving Langmuir waves or z-mode waves.