Altitude Limits for Rotating Vector Model Fitting of Pulsar Polarization

TL;DR

This paper examines the limitations of the rotating vector model (RVM) for pulsar polarization analysis at various emission altitudes, providing correction formulas to improve height estimates up to 0.3 times the light cylinder radius.

Contribution

It introduces a realistic treatment of field line sweepback effects, quantifies the altitude at which RVM estimates break down, and offers correction formulas for better emission height determination.

Findings

RVM estimates become unreliable above ~0.1 R_{LC}

Correction formulas extend accurate height estimates to ~0.3 R_{LC}

Implications for understanding emission regions in young and millisecond pulsars

Abstract

Traditional pulsar polarization sweep analysis starts from the point dipole rotating vector model (RVM) approximation. If augmented by a measurement of the sweep phase shift, one obtains an estimate of the emission altitude (Blaskiewicz, Cordes, & Wasserman). However, a more realistic treatment of field line sweepback and finite altitude effects shows that this estimate breaks down at modest altitude ~ 0.1R_{LC}. Such radio emission altitudes turn out to be relevant to the young energetic and millisecond pulsars that dominate the \gamma-ray population. We quantify the breakdown height as a function of viewing geometry and provide simple fitting formulae that allow observers to correct RVM-based height estimates, preserving reasonable accuracy to R ~ 0.3R_{LC}. We discuss briefly other observables that can check and improve height estimates.