Radio emission from tidal disruption events produced by the collision between super-Eddington outflows and the circumnuclear medium

Abstract

In this Letter, we simulate the collision between outflows from the tidal disruption of a 1M$_\odot$ main sequence star around a $10^6$M$_\odot$ black hole and an initially spherically symmetric circumnuclear cloud. We launch super-Eddington outflows self-consistently by simulating the disruption of stars on both bound and unbound initial orbits using general relativistic smoothed particle hydrodynamics. We find shocks formed as early as $\sim 10~$days after the initial stellar disruption produce prompt radio emission. The shock radius ($\approx~10^{17}$~cm), velocity ($\sim 0.15$c) and total energy ($\sim 10^{51}$ erg) in our simulations match those inferred from radio observations of tidal disruption events (TDEs). We ray-trace to produce synthetic radio images and spectra to compare with the observations. While the TDE outflow is quasi-spherical, the synchrotron emitting region is aspherical but with reflection symmetry above and below the initial orbital plane. Our synthetic spectra show continuous decay in peak frequency, matching prompt radio TDE observations. Our model supports the hypothesis that synchrotron radio flares from TDEs result from the collision between outflows and the circumnuclear material.