The true fraction of repeating fast radio bursts revealed through CHIME source count evolution

Abstract

Fast Radio Bursts (FRBs) are classified into repeaters and non-repeaters, with only a few percent of the observed FRB population from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) confirmed as repeaters. However, this figure represents only a lower limit due to the observational biases, and the true fraction of repeaters remains unknown. Correcting for these biases uncovers a notable decline in apparently non-repeating FRB detection rate as the CHIME operational time increases. This finding suggests that a significant portion of apparently non-repeating FRBs could in fact exhibit repetition when observed over more extended periods. A simple population model infers that the true repeater fraction likely exceeds 50 % with 99 % confidence, a figure substantially larger than the observed face value, even consistent with 100 %. This greater prevalence of repeaters had previously gone unnoticed due to their very low repetition rates (∼10−3.5 hr−1 on average). Hence, theoretical FRB models must incorporate these low-rate repeaters. Furthermore, our results indicate a significantly higher repeater volume number density, potentially exceeding observed values by up to 104 times, which in turn impacts comparisons with potential FRB progenitors.

Modeling Current and Future High-cadence Surveys of Repeating Fast Radio Burst Populations

“…While CHIME is a complex instrument, responsive but highly sensitive to on-site conditions that are prohibitive to model efficiently (see, e.g., Andersen et al 2023), we can infer the observability of a given event by imposing a fluence threshold of 0.4 Jy ms. This lower limit is consistent across the CHIME Catalog 1 data (CHIME/FRB Collaboration et al 2021) and the new repeater data (CHIME/FRB Collaboration 2023), and is used in similar population syntheses (Chawla 2022;Yamasaki et al 2023).…”

“…In doing this, we have tried to strike a balance between a simple analytic model and a very detailed simulation which would also include Markov Chain Monte Carlo techniques for parameter estimation. Such a simulation procedure has been followed in concurrence with this work by Yamasaki et al (2023), investigating the CHIME/ FRB source count evolution with a growing repeater population, yielding similar parameters. In many respects, we have taken an approach similar to earlier studies of the pulsar population (see, e.g., Faucher-Giguère & Kaspi 2006) where plausible models are developed that can mimic the main results.…”