Multi-epoch sampling of the radio star population with the Australian SKA Pathfinder

Abstract

The population of radio-loud stars has to date been studied primarily through either targeted observations of a small number of highly active stars or widefield, single-epoch surveys that cannot easily distinguish stellar emission from background extra-Galactic sources. As a result it has been difficult to constrain population statistics such as the surface density and fraction of the population producing radio emission in a particular variable or spectral class. In this paper we present a sample of 36 radio stars detected in a circular polarisation search of the multi-epoch Variables and Slow Transients (VAST) pilot survey with ASKAP at 887.5~MHz. Through repeat sampling of the VAST pilot survey footprint we find an upper limit to the duty cycle of M-dwarf radio bursts of 8.5 per cent, and that at least $10\pm 3$ per cent of the population should produce radio bursts more luminous than $10^{15}$ erg s${}^{-1}$ Hz${}^{-1}$. We infer a lower limit on the long-term surface density of such bursts in a shallow 1.25 mJy PSF${}^{-1}$ sensitivity survey of $9_{-7}^{+11}\times 10^{-3}$ deg${}^{-2}$ and an instantaneous radio star surface density of $1.7\pm 0.2\times 10^{-3}$ deg${}^{-2}$ on 12 min timescales. Based on these rates we anticipate $\sim 200\pm 50$ new radio star detections per year over the full VAST survey and $\sim 41000_{-9000}^{+10000}$ in next-generation all-sky surveys with the Square Kilometre Array.

14 pages, 9 figures, submitted to MNRAS