# Limit on the population of repeating fast radio bursts from the ASKAP/CRAFT lat50 survey

## TL;DR

This paper introduces a method to constrain the density of repeating fast radio bursts using survey data, and applies it to ASKAP/CRAFT, finding that FRB 121102 is likely atypical and that the population of repeaters is lower than some models predict.

## Contribution

The paper develops a new approach to limit the volumetric density of repeating FRBs based on survey non-detections, incorporating instrument sensitivity and burst properties, and applies it to real survey data.

## Key findings

- Excludes FRB 121102-like repeaters within 1.9 million Mpc³ at 95% confidence.
- Sets an upper limit of 27 Gpc⁻³ on the population density of repeating FRBs.
- Suggests a larger population of less rapidly repeating or non-repeating FRBs than previously assumed.

## Abstract

A method is presented to limit the volumetric density of repeating fast radio bursts based on the number (or lack) of repeating bursts identified in a survey. The method incorporates the instantaneous sensitivity of the instrument, its beam pattern, and the dwell time per pointing, as well as the energy and timing distribution of repeat bursts. Applied to the Australian Square Kilometre Array Pathfinder's (ASKAP's) Commensal Real-time ASKAP Fast Transients (CRAFT) `lat50' survey, the presence of an FRB similar to FRB 121102 is excluded within a volume of $1.9 \cdot 10^6$ Mpc$^3$ at 95% confidence level (C.L.). Assuming a burst energy cut-off at $10^{42}$ erg, the 95% C.L. upper limit on the population density of repeating FRBs in the current epoch is $27$ Gpc$^{-3}$, assuming isotropic (unbeamed) emission. This number is much lower than expected from even rare scenarios such as magnetar formation in gamma-ray bursts. Furthermore, the maximally allowed population under-predicts the observed number of single bursts in the survey. Comparisons with the observed dispersion measure distribution favours a larger population of less rapidly repeating objects, or the existence of a second population of non-repeating FRBs. In any scenario, FRB 121102 must be an atypical object.