A Statistical Model for the Orthogonal Modes of Polarization in Pulsar Radio Emission

Abstract

The radio emission from pulsars is modeled as the simultaneous interaction of two modes of orthogonally polarized radiation. Both modes are assumed to be completely linearly polarized, and the flux densities of the modes are represented by random variables to account for the random switching between orthogonally polarized states. Example distributions of total intensity, linear polarization, fractional linear polarization, and polarization position angle are computed with both analytical and numerical versions of the model. The model is compared to polarization observations of individual pulses from PSR B2020+28. Once allowances have been made for interstellar scintillation, the model distributions compare favorably to observed histograms, except for the position angle histograms that are wider than one would expect from a delta function that is broadened by instrumental noise. The flux densities of the orthogonal modes in PSR B2020+28 are found to be highly correlated. The depolarization of pulsar radio emission has been attributed to the orthogonal modes or to the randomization of position angle. A random, or uniform, component of the position angle will arise from superposed modes that occur with nearly equal frequency. We show that the random component of position angle in PSR B2020+28 is a consequence of depolarization by the orthogonal modes.