THE TDE ASASSN-14li AND ITS HOST RESOLVED AT PARSEC SCALES WITH THE EVN

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 similar or equal to 12. x 6 mas resolution, the emission is unresolved. At 5.0 GHz with similar or equal to 3 x 2 mas 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 4.3 mas (similar to 2 pc) 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 similar to 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.Ministry of Economy, Development, and Tourism's Millennium Science Initiative [IC120009]; CONICYT through FONDECYT [3150238, 1151445]; China-CONICYT Fellowship [CAS15002]; Chinese Academy of Sciences [XDB09000000]; NSFC [11573003]; NSF [AST-1515876, AST-1515927]; DOE Computational Science Graduate Fellowship [DE-FG02-97ER25308]; EVN project [EP096]; European Commission [283393]SCI(E)ARTICLEcristina.romero.fdi@mail.udp.cl183