Radio Observations of an Ordinary Outflow from the Tidal Disruption Event AT2019dsg

Abstract

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 similar to 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 approximate to 0.07 c, while its kinetic energy increases by a factor of about 5 from 55 to 200 days and plateaus at approximate to 4.4 x 10(48) erg thereafter. The ambient density traced by the outflow declines as radius approximate to R (-1.7) on a scale of approximate to(1-4) x 10(16) cm (approximate to 6300-25,000 R ( s )), followed by a steeper decline to approximate to 7 x 10(16) cm (approximate to 44,000 R ( s )). Allowing for a collimated geometry, we find that to reach even mildly relativistic velocities (Gamma = 2) the outflow requires an opening angle of theta ( j ) approximate to 2 degrees, 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.