Radio afterglows from tidal disruption events: An unbiased sample from ASKAP RACS

TL;DR

This study uses ASKAP RACS data to identify late-time radio emissions from optically-discovered TDEs, revealing that a significant fraction exhibit radio activity years after discovery, challenging existing models.

Contribution

It provides the first unbiased, large-scale radio follow-up of TDEs, discovering new radio emissions and estimating the fraction of TDEs with detectable radio signals.

Findings

At least 22% of optically-discovered TDEs show radio emission in RACS data.

Radio emission detected up to nearly 3000 days post-optical discovery.

Projected detection of about 20 TDEs by the VAST survey over 4 years.

Abstract

Late-time ($\sim$ 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 $\sim 3\,$ years) of the survey. Finally, we project that the ongoing higher-cadence ($\sim 2$\,months) ASKAP Variable and Slow Transients (VAST) survey can detect $\sim 20$ TDEs in its operational span (4\,yrs), given the current rate from optical surveys.