The Multiple Images of the Plasma Lensing FRB

TL;DR

This paper explores how plasma lensing can produce multiple images of FRBs, causing observable inverse dispersion effects and deviations in dispersion measure, which can help map plasma distributions in space.

Contribution

It introduces a model for plasma lensing effects on FRB signals, predicting observable inverse dispersion properties and deviations in DM across multiple images.

Findings

Inverse dispersion properties observed in some repeating FRBs.

Predicted deviations in DM across multiple images.

Potential to map plasma distributions using time delay and DM differences.

Abstract

We investigate the formation of multiple images as the radio signals from fast radio bursts (FRBs) pass through the plane of a plasma clump. The exponential model for the plasma clump is adopted to analyze the properties of the multiple images. By comparing with the classical dispersion relations, we find that one image has exhibited specific inverse properties to others, such as their delay times at high frequency is higher than that at low frequency, owing to the lensing effects of the plasma clump. We demonstrate that these inverse effects should be observable in some repeating FRBs. Our results predict deviation in the estimated DM across multiple images, consistent with the observations of FRB 121102 and FRB 180916.J0158+65. If other plasma lenses have effects similar to an exponential lens, we find that they should also give rise to the similar dispersion relation in the multiple images. For some repeating FRBs, analysis of the differences in time delay and in DM between multiple images at different frequencies can serve as a method to reveal the plasma distribution.