Linear polarization of pulsar radio emission'

We suggest that the observed linear polarization of pulsar radio emission is due to features of the emission mechanism that produce electromagnetic waves in a narrow cone around a magnetic field line. As a result, emission collected along the line of sight does not come from a single magnetic field line but from many non-parallel lines, each of which acts on an elementary emitter to generate a single linearly polarized mode. The combined emission from the bunch of rays should be nearly unpolarized at the emission site. When the rays propagate outward, the polarization of the individual ray follows that of the normal mode until the polarization limiting radius (PLR) is reached. The resulting degree of linear polarization will depend on the details of the magnetic field distribution across the emitting bunch at the PLR. We show that for the model of Gedalin et al. the PLR is deep in the magnetosphere, and we demonstrate how the linear polarization forms.