Constraining Redshifts of Unlocalised Fast Radio Bursts

TL;DR

This paper develops a framework to constrain the redshifts of unlocalised fast radio bursts (FRBs) using their dispersion measures, considering different progenitor models and cosmic evolution, to maximize scientific insights from large, unlocalised FRB samples.

Contribution

It introduces a probabilistic model linking FRB dispersion measures to redshifts across various progenitor scenarios, enabling redshift constraints without precise localisation.

Findings

Host galaxy DM contributions decrease with redshift but remain significant for AGN-like progenitors.

The model can place redshift constraints on catalogued FRBs using their DMs.

Future large surveys can use this framework to map Galactic DM contributions.

Abstract

The population of fast radio bursts (FRBs) will continue to diverge into two groups depending on their method of discovery: those which can be localised, and those which cannot. Events potentially less useful for astronomical and cosmological purposes due to limited localisation will accumulate with the advent of new facilities and continued efforts by, e.g., the SUPERB collaboration, which may require afterglows or multi-wavelength counterparts for sub-arcsecond localisation. It is important to exploit these sources to their maximum scientific potential. We perform analysis of FRB dispersion measures (DMs), considering different theoretical FRB progenitors with view to place more rigorous constraints on FRB redshifts, in particular for large statistical samples, via their DMs. We review FRB DM components, and build redshift-scalable probability distributions corresponding to different progenitor scenarios. We combine these components into a framework for obtaining FRB DM probabilities given their redshifts. Taking into account different possibilities for the evolution of progenitors across cosmic time we invert this model, thus deriving redshift constraints. Effects of varying FRB progenitor models are illustrated. While, as expected, host galaxy DM contributions become decreasingly important with increasing redshift, for AGN-like progenitor scenarios they could remain significant out to redshift 3. Constraints are placed on redshifts of catalogued FRBs with various models and increasingly realistic models may be employed as general understanding of FRBs improves. For localised FRBs, we highlight future prospects for disentangling host and intergalactic medium DM components using their respective redshift scaling. We identify a use for large samples of unlocalised FRBs resulting from upcoming flux-limited surveys, such as with CHIME, in mapping out the Milky Way contribution to the DM.