On the double-plane plasma lensing

TL;DR

This paper investigates the differences between single-plane and double-plane plasma lensing, demonstrating how observables like image positions and time delays can distinguish complex lens structures in cosmological plasma.

Contribution

It introduces a double-plane plasma lens model and compares it with single-plane models, highlighting observable differences for the first time.

Findings

Double-plane lenses produce distinguishable multiple images and time delays.

Time-domain observables are key to identifying multi-plane lensing.

Pulse shapes in fast radio bursts can reveal lens complexity.

Abstract

Plasma lensing is the refraction of low-frequency electromagnetic rays due to cold free electrons in the universe. For sources at a cosmological distance, there is observational evidence of elongated, complex plasma structures along the line of sight requiring a multi-lens-plane description. To investigate the limits of single-plane plasma lensing, we set up a double-plane lens with a projected Gaussian electron density in each lens plane. We compare double-plane scenarios with corresponding effective single-plane configurations. Our results show how double-plane lenses can be distinguished from single-plane lenses by observables, i.e. resolved multiple image positions, relative magnifications, time delays, and pulse shapes. For plasma lensing of fast radio bursts, the observed pulse shape may be dominated by the lensing effect, allowing us to neglect the intrinsic source pulse shape to distinguish different lensing configurations. The time-domain observables turn out to be the most salient features to tell multi- and single-plane lenses apart.