On the Missing Energy Puzzle of Tidal Disruption Events

TL;DR

This paper investigates the missing energy in tidal disruption events, proposing that most energy is emitted in the extreme-UV or via jets, which are often unobserved, and discusses implications for accretion and circularization timescales.

Contribution

It introduces the idea that the majority of TDE energy is hidden in EUV or jets, explaining the energy discrepancy and providing insights into the timing of energy release.

Findings

Most TDE energy is in EUV or jets, not optical/near-UV.

EUV emission is supported by mid-infrared data and testable by dust reverberation.

Energy release occurs within a few orbital periods, implying rapid circularization.

Abstract

For the majority of the tidal disruption event (TDE) candidates, the observed energy in the optical/near-UV bands is of order 10^{51} erg. We show that this observed energy is smaller than the minimum bolometric energy for the radiative inefficient accretion flow model by a factor of 10-100. We argue that this discrepancy is because the majority of the energy released is in the extreme-UV (EUV) band and/or in the form of relativistic jets beamed away from the Earth. The EUV scenario is supported by existing mid-infrared data and should be further tested by future dust reverberation observations. The jet scenario is disfavored by the radio observations of ASASSN-14li but may still be viable for other TDE candidates. We also provide evidence that, at least for some TDEs, most of the missing energy (in the EUV and/or in the form of jets) is released within a few times the orbital period of the most tightly bound material, which means (1) the circularization of the fallback stream may occur rapidly, and (2) the luminosity of the accretion flow or the jet power may not be capped near the Eddington level when the fallback rate is super-Eddington. For most other TDEs, this energy-release timescale is currently not strongly constrained.