On the Excess Dispersion in the Polarization Position Angle of Pulsar Radio Emission

Abstract

The polarization position angles (PA) of pulsar radio emission occupy a distribution that can be much wider than what is expected from the average linear polarization and the off-pulse instrumental noise. Contrary to our limited understanding of the emission mechanism, the excess dispersion in PA implies that pulsar PAs vary in a random fashion. An eigenvalue analysis of the measured Stokes parameters is developed to determine the origin of the excess PA dispersion. The analysis is applied to sensitive, well-calibrated polarization observations of PSR B1929+10 and PSR B2020+28. The analysis clarifies the origin of polarization fluctuations in the emission and reveals that the excess PA dispersion is caused by the isotropic inflation of the data point cluster formed by the measured Stokes parameters. The inflation of the cluster is not consistent with random fluctuations in PA, as might be expected from random changes in the orientation of the magnetic field lines in the emission region or from stochastic Faraday rotation in either the pulsar magnetosphere or the interstellar medium. The inflation of the cluster, and thus the excess PA dispersion, is attributed to randomly polarized radiation in the received pulsar signal. The analysis also indicates that orthogonal polarization modes (OPM) occur where the radio emission is heavily modulated. In fact, OPM may only occur where the modulation index exceeds a critical value of about 0.3.

arXiv commentAccepted for publication in ApJ

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• Polarization transfer in pulsar magnetosphere
• An empirical model for the polarization of pulsar radio emission
• The Statistics of Radio Astronomical Polarimetry: Bright Sources and High Time Resolution
• The Statistics of Radio Astronomical Polarimetry: Disjoint, Superposed, and Composite Samples
• The polarization of the drifting sub-pulses from PSR B1919+21
• Highly polarized components of integrated pulse profiles
• Orientation Angles of a Pulsar's Polarization Vector
• Exponential Fluctuations in the Modes of Orthogonal Polarization in Pulsar Radio Emission
• Polarization Patterns in Pulsar Radio Emission