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