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 3slevel of <0.14 mJy. The fast-rising, delayed radio flare is observed in our radio data set and continues to rise almost similar to 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 similar to 10(55) erg, an opening angle of similar to 7 degrees, and a relatively large viewing angle of similar to 42 degrees, 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 x10(52) 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.