A sudden period of high activity from repeating Fast Radio Burst 20201124A

TL;DR

This paper analyzes the activity, repetition rates, and luminosity function of the repeating FRB 20201124A, revealing significant changes in burst rates and constraining its luminosity distribution with a power-law model.

Contribution

It provides detailed characterization of FRB 20201124A's burst morphology, activity rates, and a maximum-likelihood estimate of its luminosity function, including a break point and index.

Findings

Repetition rate constrained to less than 3.4 per day before discovery.

Significant change in burst rate observed after initial detection.

Luminosity function follows a power-law with index -4.6, with a break at 16.6 Jy ms.

Abstract

The repeating FRB 20201124A was first discovered by CHIME/FRB in November of 2020, after which it was seen to repeat a few times over several months. It entered a period of high activity in April of 2021, at which time several observatories recorded tens to hundreds more bursts from the source. These follow-up observations enabled precise localization and host galaxy identification. In this paper, we report on the CHIME/FRB-detected bursts from FRB 20201124A, including their best-fit morphologies, fluences, and arrival times. The large exposure time of the CHIME/FRB telescope to the location of this source allows us to constrain its rates of activity. We analyze the repetition rates over different spans of time, constraining the rate prior to discovery to $< 3.4$ day$^{-1}$ (at 3$\sigma$), and demonstrate significant change in the event rate following initial detection. Lastly, we perform a maximum-likelihood estimation of a power-law luminosity function, finding a best-fit index $\alpha = -4.6 \pm 1.3 \pm 0.6$, with a break at a fluence threshold of $F_{\rm min} \sim 16.6$~Jy~ms, consistent with the fluence completeness limit of the observations. This index is consistent within uncertainties with those of other repeating FRBs for which it has been determined.