Detecting fast radio bursts at decametric wavelengths

TL;DR

This paper analyzes the potential of low-frequency radio surveys to detect fast radio bursts (FRBs), considering absorption and scattering effects, and predicts detection rates for upcoming instruments like CHIME and HIRAX.

Contribution

It evaluates the impact of free-free absorption and scattering on low-frequency FRB detection and forecasts detection rates for future surveys, highlighting the potential for increased FRB flux at low frequencies.

Findings

CHIME and HIRAX could detect 30+ FRBs per day.

UTMOST may detect 1-2 FRBs per month.

FRB flux may increase with redshift at low frequencies.

Abstract

Fast radio bursts (FRBs) are highly dispersed, sporadic radio pulses that are likely extragalactic in nature. Here we investigate the constraints on the source population from surveys carried out at frequencies $<1$~GHz. All but one FRB has so far been discovered in the 1--2~GHz band, but new and emerging instruments look set to become valuable probes of the FRB population at sub-GHz frequencies in the near future. In this paper, we consider the impacts of free-free absorption and multi-path scattering in our analysis via a number of different assumptions about the intervening medium. We consider previous low frequency surveys alongwith an ongoing survey with the University of Technology digital backend for the Molonglo Observatory Synthesis Telescope (UTMOST) as well as future observations with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and the Hydrogen Intensity and Real-Time Analysis Experiment (HIRAX). We predict that CHIME and HIRAX will be able to observe $\sim$ 30 or more FRBs per day, even in the most extreme scenarios where free-free absorption and scattering can significantly impact the fluxes below 1~GHz. We also show that UTMOST will detect 1--2 FRBs per month of observations. For CHIME and HIRAX, the detection rates also depend greatly on the assumed FRB distance scale. Some of the models we investigated predict an increase in the FRB flux as a function of redshift at low frequencies. If FRBs are truly cosmological sources, this effect may impact future surveys in this band, particularly if the FRB population traces the cosmic star formation rate.