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

Y. Cendes; K. D. Alexander; E. Berger; T. Eftekhari; P. K. G. Williams; R. Chornock

doi:10.3847/1538-4357/ac110a

paper

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

arXiv:2103.06299 · doi:10.3847/1538-4357/ac110a

Abstract

We present detailed radio observations of the tidal disruption event (TDE) AT2019dsg, obtained with the 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 the 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 $\approx 0.07 c$ , while its kinetic energy increases by a factor of about 5 from 55 to 200 days and plateaus at $\approx 5 \times 1 0^{48}$ erg thereafter. The ambient density traced by the outflow declines as $\approx R^{- 1.6}$ on a scale of $\approx (1 - 4) \times 1 0^{16}$ cm ( $\approx 6300 - 25000$ $R_{s}$ ), followed by a steeper decline to $\approx 6 \times 1 0^{16}$ cm ( $\approx 37500$ $R_{s}$ ). Allowing for a collimated geometry, we find that to reach even mildly relativistic velocities ( $Γ = 2$ ) the outflow requires an opening angle of $θ_{j} \approx 2^{\circ}$ , which is narrow even by the standards of GRB 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.

Accepted to the Astrophysical Journal

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

Abstract

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