The TDE ASASSN-14li and its host resolved at parsec scales with the EVN

TL;DR

This study uses EVN radio observations to resolve the parsec-scale structure of the TDE ASASSN-14li, exploring its nature and potential jet, outflow, or binary black hole scenarios.

Contribution

First EVN imaging of a TDE at parsec scales, revealing complex radio structures and discussing multiple possible origins.

Findings

Detected unresolved emission at 1.7 GHz.

Resolved extended structure at 5.0 GHz with two components.

Discussed scenarios including jet/outflow, non-relativistic jet, or binary black hole.

Abstract

We report European Very Long Baseline Interferometry Network (EVN) radio continuum observations of ASASSN-14li, one of the best studied tidal disruption events (TDEs) to date. At 1.7 GHz with ~12x6mas resolution, the emission is unresolved. At 5.0 GHz with ~3x2mas resolution, the radio emission shows an extended structure that can be modeled with two components: a core-like component and a fainter, possibly elongated source 4.3mas (~2pc) away. Our observations are not conclusive as to the nature of the components, but three scenarios are discussed. One possibility is a core-jet/outflow morphology, thus making of ASASSN-14li the first TDE jet/outflow directly imaged. For this case, the projected separation between the two components can only be explained by superluminal motion, rather than the lower velocities inferred from low-resolution radio observations. However, typical fast moving jets have brightness temperatures ~5 orders of magnitude higher than we find, thus making this scenario less likely. The second possibility is that we are imaging a non-relativistic jet from past AGN/TDE activity. In this case a past TDE is preferred given that the spatial extension and radio luminosity of the elongated component are consistent with the theoretical predictions for a TDE outflow. Alternatively, the two sources could indicate the presence of a binary black hole, which would then naturally explain the enhanced TDE rates of post-starburst galaxies. Future EVN observations will help us to distinguish between these scenarios.