Quasi-perpendicular Shock Acceleration and Tidal Disruption Event Radio Flares

Delayed radio flares of optical tidal disruption events (TDEs) indicate the existence of nonrelativistic outflows accompanying TDEs. The interaction of TDE outflows with the surrounding circumnuclear medium creates quasi-perpendicular shocks in the presence of toroidal magnetic fields. Because of the large shock obliquity and large outflow velocity, we find that the shock acceleration induced by TDE outflows generally leads to a steep particle energy spectrum, with the power-law index significantly larger than the universal index for a parallel shock. The measured synchrotron spectral indices of recently detected TDE radio flares are consistent with our theoretical expectation. It suggests that the particle acceleration at quasi-perpendicular shocks can be the general acceleration mechanism accounting for the delayed radio emission of TDEs.

Automated summary

Delayed radio flares of optical tidal disruption events (TDEs) indicate the presence of nonrelativistic outflows accompanying TDEs. The interaction between TDE outflows and the circumnuclear medium generates quasi-perpendicular shocks in the presence of toroidal magnetic fields. Due to the large shock obliquity and outflow velocity, the shock acceleration induced by TDE outflows results in a steep particle energy spectrum. The measured synchrotron spectral indices of recently detected TDE radio flares are consistent with this theoretical expectation, suggesting that quasi-perpendicular shocks may be the general acceleration mechanism responsible for the delayed radio emission of TDEs.