Magnetospheric curvature radiation by bunches as emission mechanism for repeating fast radio bursts

TL;DR

This paper explores how coherent curvature radiation by charged bunches in a neutron star's magnetosphere can explain the spectral, polarization, and temporal properties of repeating fast radio bursts, considering complex magnetic field geometries.

Contribution

It introduces a detailed model of FRB emission based on magnetospheric curvature radiation, incorporating polarization, spectral evolution, and magnetic field configurations.

Findings

Spectra follow multisegment broken power laws.

Linear polarization is high within a narrow beam, circular polarization increases off-beam.

Emission likely occurs in highly curved magnetic field lines, indicating multipolar magnetic structures.

Abstract

Coherent curvature radiation as the radiation mechanism for fast radio bursts (FRBs) has been discussed since FRBs were discovered. We study the spectral and polarization properties of repeating FRBs within the framework of coherent curvature radiation by charged bunches in the magnetosphere of a highly magnetized neutron star. The spectra can be generally characterized by multisegment broken power laws, and evolve as bunches move and the line of sight sweeps. Emitted waves are highly linear polarized if the line of sight is confined to the beam within an angle of $1/\gamma$, while circular polarized degree becomes strong for off-beam cases. The spectro-temporal pulse-to-pulse properties can be a natural consequence due to the magnetospheric geometry. We investigate the relationship between drift rate, central frequency and their temporal duration. The radius-to-frequency mapping is derived and simulated within the assumptions of both dipolar and quadrupolar magnetic configurations. The geometric results show that FRBs are emitted in field lines more curved than open field lines for a dipolar geometry. This suggests that there are most likely existing multipolar magnetic configurations in the emission region.