  The tidal disruption event AT2019dsg was observed from radio to X-rays and
was possibly accompanied by a high-energy neutrino. Previous interpretations
have focused on continued injection by a central engine as the source of energy
for radio emission. We show that continuous energy injection is unnecessary;
the radio data can be explained by a single ejection of plasma that supplies
all the energy needed. To support this assertion, we analyze the synchrotron
self-absorbed spectra in terms of the equipartition model. Similar to previous
analyses, we find that the energy in the radio-emitting region increases
approximately $\propto t^{0.7}$ and the lengthscale of this region grows
$\propto t$ at a rate $\simeq0.06c$. This event resembles the earliest stage of
a supernova remnant: because the ejected mass is much greater than the shocked
external mass, its velocity remains unchanged, while the energy in shocked gas
grows with time. The radio-emitting material gains energy from the outflow, not
continuing energy injection by the central object. Although energy injection
from an accreting BH cannot be completely excluded, the energy injection rate
is very different from the fallback luminosity, and maintaining constant
outflow velocity requires fine-tuning demanding further physical explanation.
If the neutrino association is real, the energy injection needed is much
greater than for the radio emission, suggesting that the detected neutrino did
not arise from the radio-emitting region.
