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

Shotaro Yamasaki^1*, Tomotsugu Goto^2,3, Chih-Teng Ling³, Tetsuya Hashimoto¹

¹Physics, NCHU, Taichung, Taiwan
²Astronomy, NTHU, Hsinchu, Taiwan
³Physics, NTHU, Hsinchu, Taiwan

* Presenter:Shotaro Yamasaki, email:shotaro.s.yamasaki@gmail.com

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 essential clue to understanding the origins of mysterious FRBs is to reveal the true fraction of repeaters. Correcting for these biases, we, for the first time, discover a notable decline in apparently non-repeating FRB detection rate as the CHIME operational time increases. This finding indicates 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 (one burst per 10^3.5 hr 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.

Keywords: Fast Radio Bursts, Transients