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>Toward an Empirical Theory of Pulsar Emission. VIII. Subbeam Circulation and the Polarization-Modal Structure of Conal Beams
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Toward an Empirical Theory of Pulsar Emission. VIII. Subbeam Circulation and the Polarization-Modal Structure of Conal Beams
The average polarization properties of conal single and double profiles directly reflect the polarization-modal structure of the emission beams that produce them. Conal component pairs exhibit large fractional linear polarization on their inside edges and virtually complete depolarization on their outside edges, whereas profiles resulting from sight-line encounters with the outside conal edge are usually very depolarized. The polarization-modal character of subbeam circulation produces conditions whereby both angular and temporal averaging contributes to this polarization and depolarization. These circumstances combine to require that the circulating subbeam systems that produce conal beams entail paired PPM and SPM emission elements that are offset from each other in both magnetic azimuth and magnetic colatitude. Or, as rotating subbeam systems produce (on average) conal beams, one modal subcone has a little larger (or smaller) radius than the other. However, these PPM and SPM "beamlets" cannot be in azimuthal phase because both sometimes dominate the emission on the extreme outside edges of the conal beam. While this configuration can be deduced from the observations, simulation of this rotating, modal subbeam system reiterates these conclusions. These circumstances are also probably responsible, along with the usual wavelength dependence of emission height, for the observed spectral decline in aggregate polarization. A clear delineation of the modal polarization topology of the conal beam promises to address fundamental questions about the nature and origin of this modal emission, and the modal parity at the outside beam edges is a fact of considerable significance. The different angular dependences of the modal beamlets suggest that the polarization modes are generated via propagation effects. This argument may prove much stronger if the modal emission is fundamentally only partially polarized. Several theories now promise quantitative comparison with the observations.
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