An off-axis relativistic jet seen in the long lasting delayed radio flare of the TDE AT 2018hyz

The Tidal Disruption Event (TDE) AT 2018hyz exhibited a delayed radio flare almost three years after the stellar disruption. Here, we report new radio observations of the TDE AT 2018hyz with the AMI-LA and ATCA spanning from a month to more than four years after the optical discovery and 200 d since the last reported radio observation. We detected no radio emission from 30-220 d after the optical discovery in our observations at 15.5 GHz down to a 3σ level of <0.14 mJy. The fast-rising, delayed radio flare is observed in our radio data set and continues to rise almost ~1580 d after the optical discovery. We find that the delayed radio emission, first detected 972 d after optical discovery, evolves as t^{4.2 ± 0.9}, at 15.5 GHz. Here, we present an off-axis jet model that can explain the full set of radio observations. In the context of this model, we require a powerful narrow jet with an isotropic equivalent kinetic energy E_{k, iso} ~ 10⁵⁵ erg, an opening angle of ~7°, and a relatively large viewing angle of ~42°, launched at the time of the stellar disruption. Within our framework, we find that the minimal collimated energy possible for an off-axis jet from AT 2018hyz is E_k ≥ 3 × 10⁵² erg. Finally, we provide predictions based on our model for the light curve turnover time, and for the proper motion of the radio emitting source.