The Dispersion Measure and Scattering of Fast Radio Bursts: Contributions from the Intergalactic Medium, Foreground Halos, and Hosts

Abstract

Abstract We investigate the dispersion measure (DM) and scattering of fast radio bursts (FRBs) by the intergalactic medium (IGM), foreground halos, and host halos using cosmological hydrodynamical simulation. We find that the median DM caused by foreground halos is around 30% of that caused by the IGM, but it has a much larger variance. The DM induced by hosts deviates from a log-normal distribution but exhibits an extended distribution in the range of with a median value . Then we produce mock FRB sources, assuming a uniform distribution in the range , to consider the propagation effect of IGM, foreground, and host halos on FRB signals simultaneously. The DM distribution of mock sources agrees well with the observation. The fitted DM–redshift relation of the mock sources can provide a rough estimation of the redshifts of observed events with errors . The distribution of mock sources in the DM scattering time (τ) space can also match the observation, assuming a Kolmogorov turbulence model where the inner and outer scales are 1000 km to 1 au and 0.2–10 pc, respectively. Finally, we estimate the relative importance of these media for DM and τ in our models. The IGM and host halos are the primary and secondary sources for the extragalactic DM ( ). Meanwhile, the contribution from foreground halos increases as increases. The host and foreground halos may be the most important media for scattering. Statistically, the latter may dominate the scattering of events with .