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

TL;DR

This study reveals that over half of all FRBs may be repeaters, a much higher fraction than observed, due to observational biases and low repetition rates, impacting theoretical models and progenitor comparisons.

Contribution

It provides the first robust estimate of the true FRB repeater fraction exceeding 50%, correcting for observational biases and low repetition rates.

Findings

True repeater fraction likely exceeds 50% with 99% confidence.

Repetition rates are around 10^{-3.5} hr^{-1}, much lower than previously assumed.

Recurrent FRBs could be up to 10^4 times more numerous than observed.

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 ($\sim$10$^{-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 10$^4$ times, which in turn impacts comparisons with potential FRB progenitors.