Radio Afterglows from Tidal Disruption Events: an Unbiased Sample from ASKAP RACS

Late-time (∼ year) radio follow-up of optically-discovered tidal disruption events (TDEs) is increasingly resulting in detections at radio wavelengths, and there is growing evidence for this late-time radio activity to be common to the broad class of sub-relativistic TDEs. Detailed studies of some of these TDEs at radio wavelengths are also challenging the existing models for radio emission. Using all-sky multi-epoch data from the Australian Square Kilometre Array Pathfinder (ASKAP), taken as a part of the Rapid ASKAP Continuum Survey (RACS), we searched for radio counterparts to a sample of optically-discovered TDEs. We detected late-time emission at RACS frequencies (742-1032 MHz) in five TDEs, reporting the independent discovery of radio emission from TDE AT2019ahk and extending the time baseline out to almost 3000 days for some events. Overall, we find that at least 22^+15_-11% of the population of optically-discovered TDEs has detectable radio emission in the RACS survey, while also noting that the true fraction can be higher given the limited cadence (2 epochs separated by ∼ 3 years) of the survey. Finally, we project that the ongoing higher-cadence (∼ 2 months) ASKAP Variable and Slow Transients (VAST) survey can detect ∼ 20 TDEs in its operational span (4 yrs), given the current rate from optical surveys.