The Transition between Nonorthogonal Polarization Modes in PSR B2016+28 at 1404 MHz

Polarization observations of the radio emission from PSR B2016+28 at 1404 MHzreveal properties that are consistent with two, very different, interpretationsof the pulsar's viewing geometry. The pulsar's average polarization propertiesshow a rapid change in position angle (PA) near the pulse center, suggestingthat the observer's sightline nearly intersects the star's magnetic pole. Butsingle pulse, polarization observations of the pulsar show nearly orthogonalmodes of polarization following relatively flat and parallel PA trajectoriesacross the pulse, suggesting that the sightline is far from the pole.Additionally, PA histograms reveal a "modal connecting bridge", of unknownorigin, joining the modal PA trajectories over much of the pulse and followingthe rapid PA change shown in the average data. The nonorthogonality ofpolarization modes is incorporated in a statistical model of radio polarizationto account for the deviations from mode orthogonality that are observed in thepulsar. The model is used to interpret the rapid PA change and modal connectingbridge as a longitudinally-resolved transition between modes of nonorthogonalpolarization. Thus, the modal PA trajectories are argued to reflect thepulsar's true viewing geometry. This interpretation is consistent with thepulsar's morphological classification, preserves the Radhakrishnan & Cookemodel of pulsar radio emission, and avoids the complication that the modalconnecting bridge might be produced by some other emission mechanism. Thestatistical model's ability to simulate the rich variety of polarizationproperties observed in the emission lends additional support to the model'sapplicability and its underlying assumption that the polarization modes occursimultaneously.Comment: Accepted for publication in Ap