Dynamical Unification of Tidal Disruption Events

Abstract

The ∼100 tidal disruption events (TDEs) observed so far exhibit a wide range of emission properties both at peak and over their lifetimes. Some TDEs radiate predominantly at X-ray energies, while others radiate chiefly at UV and optical wavelengths. While the peak luminosities across TDEs show distinct properties, the evolutionary behavior can also vary between TDEs with similar peak emission properties. In particular, for optical TDEs, while their UV and optical emissions decline somewhat following the fallback pattern, some events can greatly rebrighten in X-rays at late time. In this Letter, we conduct three-dimensional general relativistic radiation magnetohydrodynamics simulations of TDE accretion disks at varying accretion rates in the regime of super-Eddington accretion. We make use of Monte Carlo radiative transfer simulations to calculate the reprocessed spectra at various inclinations and at different evolutionary stages. We confirm the unified model proposed by Dai et al., which predicts that the observed emission largely depends on the viewing angle of the observer with respect to the disk orientation. Furthermore, we find that disks with higher accretion rates have elevated wind and disk densities, which increases the reprocessing of the high-energy radiation and thus generally augments the optical-to-X-ray flux ratio along a particular viewing angle. This implies that at later times, as the accretion level declines, we expect that more X-rays will leak out along intermediate viewing angles. Such dynamical model for TDEs can provide a natural explanation for the diversity in the emission properties observed in TDEs at peak and along their temporal evolution.

The rise and fall of the iron-strong nuclear transient PS16dtm

“…However, the fact that the SED cannot be described with a single blackbody does not exclude the interpretation of PS16dtm as a TDE. According to the radiative transfer calculations by Roth et al (2016) and Thomsen et al (2022), the optical/UV continuum of TDEs is not necessarily described by a single blackbody. In addition, it is possible that the SEDs of TDEs in AGN are different compared to those in inactive galaxies due to the preexisting AGN disk, as suggested by the simulations in Chan et al (2021).…”

A Bright First Day for Tidal Disruption Events

“…Dai et al (2018) proposed a unified model for a typical TDE system, including the highly asymmetric geometry of the radiation-supported thick disk, optically thick wind, and hot corona or jet. This model suggests that the emission from such systems will naturally cover both the optical/UV and soft X-ray bandwidth, with viewing angle effects dominating the appearance in different wave bands (see also Thomsen et al 2022).…”

Modeling continuum polarization levels of tidal disruption events based on the collision-induced outflow model

“…The first scenario suggests that the accretion disk emission is reprocessed to less energetic wavelengths by material around the SMBH (e.g., Loeb & Ulmer 1997;Strubbe & Quataert 2009;Guillochon et al 2014;Roth et al 2016). A unification scenario of TDEs has been proposed (Dai et al 2018;Thomsen et al 2022) tha describes their geometry with a thick, super-Eddington accretion disk. Because of inefficient accretion (mostly at early times), a polar relativistic jet as well as optically thick outflows of material are launched (Metzger & Stone 2016) and thus reprocess radiation to longer wavelengths.…”