2021/10/30 by Lyutikov, Maxim
#FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE)
paper · doi:10.48550/arxiv.2111.00281
Fast Radio Bursts (FBRs) show highly different polarization properties: high/small RMs, high/small circular/linear fractions. We outline a complicated picture of polarization propagation in the inner parts of the magnetars' winds, at scales ∼ few to hundreds of light cylinder radii. The key point is the Faraday rotation of linear polarization in highly magnetized symmetric pair plasma, a ∝ B2 effect. Position angle (PA) rotation rate is maximal for propagation across the magnetic field and disappears only for parallel propagation. In the highly magnetized regime, ω≪ ωB, it becomes independent of the magnetic field. Very specific properties of PA(λ) (scaling of the rotation angle with the observed wavelength λ) can help identify/sort out the propagation effects. Two basic regimes in pair plasma predict PA ∝ λ and ∝ λ3 (depending on the magnetic dominance); both are different from the conventional plasma's PA = RM λ2. This is the main prediction of the model. A number of effects, all sensitive to the underlying parameters, contribute to the observed complicated polarization patterns: streaming of plasma along magnetic field lines near the light cylinder, Faraday depolarization, effects of limiting polarization, the associated effect of linear-circular conversion, and synchrotron absorption.