Altitude-dependent polarization in radio pulsars

TL;DR

This paper derives the relation between polarization angle delay and emission altitude in radio pulsars, clarifies its cause as corotation effects, and provides practical formulas for data modeling, also discussing unusual polarization shifts.

Contribution

It presents a simple derivation of the delay-radius relation, emphasizing corotation's role, and offers altitude-dependent formulas for polarization angle curves applicable to radio data analysis.

Findings

Delay-radius relation is due to corotation, not aberration.

Altitude-dependent formulas are expressed through observables.

Comparison shows analytical approximations perform well at high altitudes.

Abstract

Because of the corotation, the polarization angle (PA) curve of a pulsar lags the intensity profile by 4r/Rlc rad in pulse phase. I present a simple and short derivation of this delay-radius relation to show that it is not caused by the aberration (understood as the normal beaming effect) but purely by contribution of corotation to the electron acceleration in the observer's frame. Available altitude-dependent formulae for the PA curve are expressed through observables and emission altitude to make them immediately ready to use in radio data modelling. The analytical approximations for the altitude-dependent PA curve are compared with exact numerical results to show how they perform at large emission altitudes. I also discuss several possible explanations for the opposite-than-normal shift of PA curve, exhibited by the pedestal emission of B1929+10 and B0950+08.