X-Ray Variability and Photosphere Evolution during Accretion Disk Formation in Tidal Disruption Events
Year: 2026
Type: article
Abstract: The early time emission in tidal disruption events (TDEs) originates from both accretion and shocks, producing photons that eventually emerge from an inhomogeneous photosphere. We model disk formation following debris stream self-intersection in a TDE using three-dimensional, frequency-integrated, and multigroup radiation hydrodynamics simulations. We find a more circularized disk forms about 24 days following the stream–stream collision, once the mass fallback rate passes its peak and the debris stream density decreases. Despite the absence of a circularized disk at early times, various shocks and the asymmetric photosphere are sufficient to drive a wide range of X-ray-to-optical ratios and soft X-ray variability. We find that with strong apsidal precession, the first light is from the stream–stream collision. It launches an optically thick outflow, but only produces modest prompt emission. The subsequent optical and UV light-curve rise is mainly powered by shocks in the turbulent accretion flow close to the black hole. The optical–UV luminosity peaks roughly when the disk forms and shock-driven outflows subside. Radiation pressure clears the polar region and creates optically thin channels. We obtain the broadband spectral energy distribution (SED) by postprocessing multigroup simulations with 16–20 frequency groups. The SED has a blackbody component that peaks in the extreme-UV. The soft X-ray component either resembles a thermal tail, or can be described by a power law associated with bulk Compton scattering. The blackbody parameters are broadly consistent with observed optical TDEs and vary weakly with viewing angle, but the soft X-ray emission is highly angle dependent.
Source: The Astrophysical Journal
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
Funders: National Science Foundation, National Aeronautics and Space Administration, Gordon and Betty Moore Foundation, California Institute of Technology, University of Virginia, Yuhan, Flatiron Health, Ames Research Center, College and Graduate School of Arts and Sciences, Office of Advanced Cyberinfrastructure, Kavli Institute for Theoretical Physics, University of California, Santa Barbara
OpenAlex ID: W7213266504