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Published October 1, 2022 | public
Journal Article

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.

Additional Information

We thank K. Auchettl, C. Bonnerot, M. Bulla, J. Garcia, S. Gezari, E. Kara, D. Kasen, C. Knigge, G. Leloudas, B. Mockler, N. Stone, and S. van Velzen for useful discussions. We also acknowledge the anonymous referee for constructive comments. L.T., T.K., and L.D. acknowledge the support from the Hong Kong Research Grants Council (HKU27305119, HKU17304821) and the National Natural Science Foundation of China (HKU12122309). E.R.-R. is grateful for support from the Heising-Simons Foundation, NSF (AST-1615881, AST-1911206, and AST-1852393), Swift (80NSSC21K1409, 80NSSC19K1391), and Chandra (GO9-20122X). This material is based on work supported by the National Science Foundation Graduate Research Fellowship under grant No. DGE-1745301. The simulations carried out for this project were performed on the HPC computing facilities offered by ITS at HKU and the Tianhe-2 supercluster.

Additional details

Created:
August 22, 2023
Modified:
October 24, 2023