Theory of striped dynamic spectra of the Crab pulsar high-frequency interpulse

TL;DR

This paper develops a theory explaining the zebra-like spectral patterns in the Crab pulsar's high-frequency interpulse, linking interference effects to magnetospheric plasma and gravitational lensing, and predicts observable changes at high frequencies.

Contribution

The study introduces a novel model connecting interference patterns to pulsar magnetosphere properties and predicts a frequency-dependent change in the zebra pattern observable with current telescopes.

Findings

Interference maxima caused by ray propagation explain the spectral bands.

The plasma density profile follows n_e ∝ r^(-3), consistent with theory.

Predicted pattern changes occur between 42 GHz and 650 GHz.

Abstract

A theory of the spectral "zebra" pattern of the Crab pulsar's high-frequency interpulse (HFIP) radio emission is developed. The observed emission bands are interference maxima caused by multiple ray propagation through the pulsar magnetosphere. The high-contrast interference pattern is the combined effect of gravitational lensing and plasma de-lensing of light rays. The model enables space-resolved tomography of the pulsar magnetosphere, yielding a radial plasma density profile of $n_{e}\propto r^{-3}$, which agrees with theoretical insights. We predict the zebra pattern trend to change at a higher frequency when the ray separation becomes smaller than the pulsar size. This frequency is predicted to be in the range between 42 GHz and 650 GHz, which is within the reach of existing facilities like ALMA and SMA. These observations hold significant importance and would contribute to our understanding of the magnetosphere. Furthermore, they offer the potential to investigate gravity in the strong field regime near the star's surface.