Imprint of local environment on fast radio burst observations

TL;DR

This paper explores how the local environment around fast radio burst sources affects the observed signals, revealing that plasma interactions cause variability in dispersion and rotation measures, and influence burst propagation.

Contribution

It introduces a model of local plasma effects on FRB signals, highlighting how wave amplitude impacts dispersion, rotation, and absorption, which can inform about the source environment.

Findings

Dispersion and rotation measures vary with burst luminosity and frequency.

Free-free absorption is suppressed for strong waves, enabling low-frequency burst propagation.

Analyzing burst populations can reveal properties of the local environment.

Abstract

When fast radio burst (FRB) waves propagate through the local (< 1 pc) environment of the FRB source, electrons in the plasma undergo large-amplitude oscillations. The finite-amplitude effects cause the effective plasma frequency and cyclotron frequency to be dependent on the wave strength. The dispersion measure and rotation measure should therefore vary slightly from burst to burst for a repeating source, depending on the luminosity and frequency of the individual burst. Furthermore, free-free absorption of strong waves is suppressed due to the accelerated electrons' reduced energy exchange in Coulomb collisions. This allows bright low-frequency bursts to propagate through an environment that would be optically thick to low-amplitude waves. Given a large sample of bursts from a repeating source, it would be possible to use the deficit of low-frequency and low-luminosity bursts to infer the emission measure of the local intervening plasma and its distance from the source. Information about the local environment will shed light on the nature of FRB sources.