Toward an empirical theory of pulsar emission. V. On the circular polarization in pulsar radiation

The circular polarization associated with pulsar emission is examined phenomenologically. Virtually all circular polarization is observed in core components - that is, in core-single profiles and in the central components of triple and five-component profiles. Two extreme types of circular signature are identified in the observations: (1) an antisymmetric type wherein the circular polarization changes sense in midpulse, and (2) a symmetric type wherein it is predominantly of one sense. It is found that circular polarization of the antisymmetric type is strongly correlated with the sense of rotation of the linear position angle. Transitions from positive (LH) to negative (RH) are found to accompany negative (clockwise) rotations of the position angle and vice versa. The correlation requires that the antisymmetric circular polarization is also a purely geometric property of the emission process. Curvature radiation will have significant net circular polarization if there are gradients in the emissivity over angular scales comparable with the emission cone of a single charge. Furthermore, no net circular polarization is produced if the emissivity is circularly symmetric about the magnetic dipole axis. 37 refs