Modeling Fast Radio Burst Dispersion and Scattering Properties in the First CHIME/FRB Catalog

TL;DR

This study uses Monte Carlo simulations to analyze the dispersion and scattering properties of FRBs in the CHIME/FRB catalog, exploring different environmental models to explain observed scattering timescales.

Contribution

It introduces a comprehensive population synthesis model considering multiple scattering media, providing new insights into the environments of FRBs and their propagation effects.

Findings

Host galaxy ISM alone cannot explain scattering timescales.

Additional scattering from CGM and circumburst media is marginally consistent with observations.

FRBs likely reside offset from galaxy centers, not along spiral arms.

Abstract

We present a Monte Carlo-based population synthesis study of fast radio burst (FRB) dispersion and scattering focusing on the first catalog of sources detected with the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) project. We simulate intrinsic properties and propagation effects for a variety of FRB population models and compare the simulated distributions of dispersion measures (DMs) and scattering timescales with the corresponding distributions from the CHIME/FRB catalog. Our simulations confirm the results of previous population studies, which suggested that the interstellar medium of the host galaxy alone (simulated based on the NE2001 model) cannot explain the observed scattering timescales of FRBs. We therefore consider additional sources of scattering, namely, the circumgalactic medium (CGM) of intervening galaxies and the circumburst medium whose properties are modeled based on typical Galactic plane environments. We find that a population of FRBs with scattering contributed by these media is marginally consistent with the CHIME/FRB catalog. In this scenario, our simulations favor a population of FRBs offset from their galaxy centers over a population which is distributed along the spiral arms. However, if the models proposing the CGM as a source of intense scattering are incorrect, then we conclude that FRBs may inhabit environments with more extreme properties than those inferred for pulsars in the Milky Way.