2021ApJ...919..127C

We present detailed radio observations of the tidal disruption event (TDE) AT2019dsg, obtained with the Karl G. Jansky Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA), and spanning 55-560 days post disruption. We find that the peak brightness of the radio emission increases until ∼200 days and subsequently begins to decrease steadily. Using a standard equipartition analysis, including the effects of synchrotron cooling as determined by the joint VLA-ALMA spectral energy distributions, we find that the outflow powering the radio emission is in roughly free expansion with a velocity of ≃0.07 c, while its kinetic energy increases by a factor of about 5 from 55 to 200 days and plateaus at ≃4.4 x 10⁴⁸ erg thereafter. The ambient density traced by the outflow declines as radius ≃R^–1.7 on a scale of ≃(1-4) x 10¹⁶ cm (≃6300-25,000 R_s), followed by a steeper decline to ≃7 x 10¹⁶ cm (≃44,000 R_s). Allowing for a collimated geometry, we find that to reach even mildly relativistic velocities (Γ = 2) the outflow requires an opening angle of θ_j ≃ 2°, which is narrow even by the standards of gamma-ray burst jets; a truly relativistic outflow requires an unphysically narrow jet. The outflow velocity and kinetic energy in AT2019dsg are typical of previous non-relativistic TDEs, and comparable to those from type Ib/c supernovae, raising doubts about the claimed association with a high-energy neutrino event.