Coherent origin of peculiar radio pulsar polarization

Jarosław Dyks

Radio pulsar data reveal a range of peculiar polarization phenomena, such as 1) jumps between orthogonal polarization modes (OPMs) that are coincident with both the maximum circular polarization fraction V /I and a non-vanishing linear polarization fraction L/I, 2) the same sign of V in both OPMs, 3) strong distortions of polarization angle (PA) from the rotating vector model (RVM) that are especially common in core components, and 4) non-orthogonal PA jumps. It is shown that these effects can be understood in terms of coherent addition of orthogonally polarized natural mode waves, with their relative phase lag and flux ratio being the key parameters that determine the apparent polarization. The phenomena can be efficiently studied with an empirical model which assumes that the emitted low-altitude signal is split into the natural propagation mode waves in a high-altitude ‘intervening’ region. The waves acquire a relative phase lag and combine coherently after they leave the region. In this model, the observed RVM-like PA curve is fixed by the B-field geometry at the high altitude, whereas the relative flux of the combining waves is parametrized by the mismatch of projected B-field geometry in the emission and intervening regions. Such approach has been successfully applied to peculiar polarization phenomena observed in PSR B1913+16, B1237+25, B1919+21 and B1933+16.

Proceedings of the Polish Astronomical Society, vol. 7, 70-75 (2018)

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