On the true fractions of repeating and non-repeating FRB sources

TL;DR

This study uses Monte Carlo simulations to explore the true fractions of repeating and non-repeating FRB sources, suggesting most FRBs may be repeaters and predicting how observed repeater fractions evolve over time.

Contribution

It introduces a model to estimate the intrinsic repeater fraction among FRBs and predicts observational signatures to distinguish between all sources repeating or not.

Findings

The observed repeater fraction initially increases, peaks, then declines over time.

Current data suggests a lower limit of 0.1 days for the lifetime of repeaters.

Future observations may find a peak repeater fraction below 0.04, challenging the all-repeater hypothesis.

Abstract

Observationally, fast radio bursts (FRBs) can be divided into repeating and apparently non-repeating (one-off) ones. It is unclear whether all FRBs repeat and whether there are genuine non-repeating FRBs. We attempt to address these questions using Monte Carlo simulations. We define a parameter $T_c$ at which the accumulated number of non-repeating sources becomes comparable to the total number of the repeating sources, which is a good proxy to denote the intrinsic repeater fraction among FRBs. Assuming that both types of sources exist and that their burst energies follow power law distributions, we investigate how the {\em observed} repeater fraction evolves with time for different parameters. If the lifetime of repeaters is sufficiently long so that the evolutionary effect can be neglected within the observational time span, unless $T_c \rightarrow \infty$ (i.e. there is no genuine non-repeating FRB source) the observed repeater fraction should increase with time first, reach a peak, and then decline. The peak time $T_p$ and the peak fraction $F_{\rm r,obs,p}$ depend on $T_c$ and other repeating rate parameters. With the current data, we pose a lower limit $T_c > 0.1$ d for reasonable parameter values. We predict that future continuous monitoring of FRBs with CHIME or similar wide-field radio telescopes would obtain an $F_{\rm r,obs}$ less than $0.04$. The detection of a smaller peak value $F_{\rm r,obs,p}<0.04$ in the near future would disfavor the ansatz that "all FRB sources repeat".