Saturation of the filamentation instability and dispersion measure of Fast Radio Bursts

TL;DR

This paper investigates how filamentation in relativistic magnetar winds affects the propagation and dispersion measure of Fast Radio Bursts, revealing that the wind can significantly alter observed signals and their variability.

Contribution

It introduces a model of FRB filamentation in magnetar winds, showing how it influences dispersion and wave propagation, with implications for interpreting FRB observations.

Findings

Dispersion relation is similar to homogeneous plasma but depends on sheet separation.

Magnetar winds can contribute significantly to FRB dispersion measure.

Induced Compton scattering is suppressed in filamented plasma.

Abstract

Nonlinear effects are crucial for the propagation of Fast Radio Bursts (FRBs) near the source. We study the filamentation of FRBs in the relativistic winds of magnetars, which are commonly invoked as the most natural FRB progenitors. As a result of filamentation, the particle number density and the radiation intensity develop strong gradients along the direction of the wind magnetic field. A steady state is reached when the plasma pressure balances the ponderomotive force. In such a steady state, particles are confined into periodically spaced thin sheets, and electromagnetic waves propagate between them as in a waveguide. We show that: (i) The dispersion relation resembles that in the initial homogeneous plasma, but the effective plasma frequency is determined by the separation of the sheets, not directly by the mean particle density. (ii) The contribution of relativistic magnetar winds to the dispersion measure of FRBs could be several orders of magnitude larger than previously thought. The dispersion measure of the wind depends on the properties of individual bursts (e.g. the luminosity), and therefore can change significantly among different bursts from repeating FRBs. (iii) Induced Compton scattering is suppressed because most of the radiation propagates in near vacuum regions.