Propagation Effects on the Polarization of Pulsar Radio Emission

Abstract

The properties of the natural wave modes of a pulsar magnetosphere are derived in a simple way by appealing to the 'low-density limit'. The properties are evaluated explicitly for a general version of the cold plasma model which includes relativistic streaming motions, and it is argued that this model is probably adequate for pulsar magnetospheres. The observed circular polarization in pulsar radio emission could arise as a propagation effect; the conditions under which initially linear polarization could be converted into partially circularly polarized radiation are summarized. The observed 'orthogonal modes' of polarization could be due to components in the two natural modes having slightly different ray paths. The angular separation of the two rays is found to be a strong function of frequency (!!(), ~ 4 x 108 ne/ /2), and it is suggested that a study of the frequency dependence of 'orthogonal modes' could provide useful information.