Identifying axion conversion in compact star magnetospheres with radio-wave polarization signatures

TL;DR

This paper models the radio-wave polarization signatures of axion conversion in neutron star magnetospheres, proposing observable features like narrow bandwidth and polarization patterns to detect axions as dark matter candidates.

Contribution

It provides detailed calculations of axion-induced radio signals' intensity and polarization, incorporating plasma and relativistic effects, and predicts distinctive observational signatures.

Findings

Radio signals have narrow bandwidths.

Distinct polarization features are predicted.

Plasma and relativistic effects significantly influence polarization.

Abstract

The axion is well motivated in physics. It solves the strong charge conjugation-parity reversal problem CP in fundamental physics and the dark matter problem in astronomy. Its interaction with the electromagnetic field has been expected but never detected experimentally. Such particles may convert to radio waves in the environment with a strong magnetic field. Inspired by the idea, various research groups have been working on theoretical modeling and radio data analysis to search for the signature of radio signals generated by the axion conversion in the magnetosphere of compact stars, where the surface magnetic field as strong as $10^{13}$-$10^{14}$ G is expected. In this work, we calculate the observational properties of the axion-induced radio signals (AIRSs) in the neutron star magnetosphere, where both the total intensity and polarization properties of radio emission are derived. Based on the ray tracing method, assuming 100% linear polarization of radio waves generated in each conversion, we compute the polarization emission profile concerning different viewing angles. We note that plasma and general relativistic effects are important for the polarization properties of AIRSs. Our work suggests that AIRSs can be identified by the narrow bandwidth and distinct polarization features.