FRB event rate counts II --- fluence, redshift and dispersion measure distributions

TL;DR

This paper investigates the statistical properties of FRBs, such as fluence and dispersion measure, to infer their cosmic distribution, evolution, and physical origins, highlighting the role of intergalactic medium effects and luminosity functions.

Contribution

It introduces a model-independent framework linking FRB observable distributions to their physical and cosmological properties, including the impact of Helium reionization.

Findings

FRB luminosity function is flatter than critical, enabling detection at large distances.

Dispersion measure can serve as a proxy for distance, with at least 50% attributable to intergalactic medium.

Evidence of Helium reionization effects in dispersion measure distribution.

Abstract

We examine how the various observable statistical properties of the FRB population relate back to their fundamental physical properties in a model independent manner. We analyse the flux density and fluence distributions of Fast Radio Bursts (FRBs) as a tool to investigate their luminosity distance distribution and the evolution of their prevalence throughout cosmic history. We examine in detail particular scenarios in which the burst population follows some power of the cosmic star formation rate. FRBs present an important additional measurable over source counts of existing cosmological populations, namely the dispersion measure. Based on the known redshift of FRB121102 (the repeater) we expect at least 50% of the dispersion measure to be attributable to the inter-galactic medium and hence it can be used as a proxy for distance. We develop the framework to interpret the dispersion measure distribution, and investigate how the effect of Helium reionization in the intergalactic medium is evident in this distribution. Examination of existing data suggests that the FRB luminosity function is flatter than a critical slope, making FRBs easily detectable to large distances; in this regime the reduction in flux density with distance is outweighed by the increase in the number of bright bursts within the search volume.