The influence of plasma lensing magnification to the luminosity function of fast radio bursts

TL;DR

This paper investigates how plasma lensing by ionized gas clumps affects the observed luminosity function of fast radio bursts, revealing potential biases in population studies due to magnification and demagnification effects.

Contribution

It models plasma lensing effects on FRB luminosity functions using Gaussian plasma clumps and analytical models, highlighting the impact on observed source brightness and bias.

Findings

Plasma lensing can demagnify sources below detection thresholds.

Magnification can produce anomalously bright high-luminosity sources.

Scattering effects can suppress plasma lensing impacts.

Abstract

Small scale clumps of ionized gas have been suggested by observations in interstellar medium and circumgalactic medium. The propagation of radio signals can be deflected by these plasma clumps, i.e. plasma lensing. One observable consequence is the magnification and demagnification of background sources. These effects distort the observed luminosity function and potentially introduce bias into population studies. In this work, we investigate these effects on fast radio bursts using Gaussian plasma clumps distributed across multiple lens planes within a small field of view. The central electron density for each clump is sampled from uniform, log-normal, and Gaussian distributions. Two analytical models are employed to mimic the intrinsic luminosity function. Our results show that plasma lensing can modify the observed luminosity functions. On one hand, our model shows that radio sources may be demagnified below the detection threshold, the strength varies between ~1-15% depending on the ionized gas model and the source redshift. On the other hand, magnification can produce anomalously bright sources at the high luminosity end. Both effects introduce potential biases in inferred source properties. The lensing strength correlates with the power spectrum of free electron density. However, scattering effect in the host galaxy or in the Milky Way can suppress the plasma lensing effects.