Circular polarisation of synchrotron radiation in high magnetic fields

Abstract

The general model for incoherent synchrotron radiation has long been known, with the first theory being published by Westfold in $1959$ and continued by Westfold and Legg in $1968$. When this model was first developed it was applied to radiation from Jupiter, with a magnetic field of $\approx$ 1 G. Pulsars have a magnetic field of $\approx 10^{12}$ G. The Westfold and Legg model predict a circular polarization which is proportional to the square root of the magnetic field, and consequently predicts greater than 100 per cent circular polarization at high magnetic fields. Here a new model is derived based upon a more detailed analysis of the pitch angle distribution. This model is concerned with the frequency range $f_{B_0}/\gamma <<f\lesssim f_{B_0}$, noting that $f_{B_0}=2.7\times 10^{7}B$, which for a relatively high magnetic field ($\sim 10^6-10^8$ Gauss) leaves emission in the optical range. This is much lower than the expected frequency peak for a mono-energetic particle of $0.29\frac{3eB}{4\pi m_{e}c}{\gamma }^2$. We predict the circular polarization peaks around $10^7$G in the optical regime with the radiation almost $15$ per cent circularly polarized. The linear polarization changes from about $60$ to $80$ per cent in the same regime. We examine implications of this for pulsar studies.

arXiv comment10 pages accepted for publication in MNRAS

References in corpus (6)

• Optical polarisation of the Crab pulsar: precision measurements and comparison to the radio emission
• High-energy emission from the pulsar striped wind: a synchrotron model for gamma-ray pulsars
• Outer gap accelerator closed by magnetic pair-creation process
• Gamma-ray Emission from the Vela Pulsar Modeled with the Annular Gap and Core Gap
• The Galway Astronomical Stokes Polarimeter: An All-Stokes Optical Polarimeter with Ultra-High Time Resolution
• Inverse Mapping of Polarised Optical Emission from Pulsars : Basic Formulation and Determination of Emission Altitude

Cited by in corpus (8)

• Polarimetric evidence of a white dwarf pulsar in the binary system AR Scorpii
• A recent change in the optical and γ-ray polarization of the Crab nebula and pulsar
• Linear Polarization, Circular Polarization, and Depolarization of Gamma-ray Bursts: A Simple Case of Jitter Radiation
• Detecting primordial gravitational waves with circular polarization of the redshifted 21 cm line: I. Formalism
• Signatures of leptophilic t-channel dark matter from active galactic nuclei
• Detecting primordial gravitational waves with circular polarization of the redshifted 21 cm line: II. Forecasts
• Polarisation of high energy gamma-rays after scattering
• Circular polarisation: a new probe of dark matter and neutrinos in the sky