Late Time Radio Emission from X-ray Selected Tidal Disruption Events
  We present new observations with the Karl G. Jansky Very Large Array of seven
X-ray-selected tidal disruption events (TDEs). The radio observations were
carried out between 9 and 22 years after the initial X-ray discovery, and,
thus, probe the late-time formation of relativistic jets and jet interactions
with the interstellar medium in these systems. We detect a compact radio source
in the nucleus of the galaxy IC 3599 and a compact radio source that is a
possible counterpart to RX J1420.4+5334. We find no radio counterparts for five
other sources with flux density upper limits between 51 and 200 microJy (3
sigma). If the detections truly represent late radio emission associated with a
TDE, then our results suggest that a fraction >~ 10% of X-ray-detected TDEs are
accompanied by relativistic jets. We explore several models for producing late
radio emission, including interaction of the jet with gas in the circumnuclear
environment (blast wave model), and emission from the core of the jet itself.
Upper limits on the radio flux density from archival observations suggest that
the jet formation may have been delayed for years after the TDE, possibly
triggered by the accretion rate dropping below a critical threshold of ~
10^{-2} -- 10^{-3} Mdot_Edd. The non-detections are also consistent with this
scenario; deeper radio observations can determine whether relativistic jets are
present in these systems. The emission from RX J1420.4+5334 is also consistent
with the predictions of the blast wave model, however the radio emission from
IC 3599 is substantially underluminous, and its spectral slope is too flat,
relative to the blast wave model expectations. Future radio monitoring of IC
3599 and RX J1420.4+5334 will help to better constrain the nature of the jets
in these systems.
