A multi-dimensional view of a unified model for TDEs

TL;DR

This study advances the understanding of TDE spectral energy distributions by employing 2.5D Monte Carlo radiative transfer simulations that incorporate multiple atomic species and the non-spherical geometry of outflows, revealing the significant impact of multi-dimensional effects.

Contribution

It introduces a 2.5D radiative transfer model with multiple atomic species, improving upon previous quasi-1D models for TDE outflows and spectra.

Findings

Inclination affects observed spectra but does not fully explain the OXR range.

Including metals alters spectra with stronger UV lines and impacts OXR variation.

Multi-dimensional photon transport significantly influences emergent SEDs.

Abstract

Tidal disruption events (TDEs) can generate non-spherical, relativistic and optically thick outflows. Simulations show that the radiation we observe is reprocessed by these outflows. According to a unified model suggested by these simulations, the spectral energy distributions (SEDs) of TDEs depend strongly on viewing angle: low [high] optical-to-X-ray ratios (OXRs) correspond to face-on [edge-on] orientations. Post-processing with radiative transfer codes have simulated the emergent spectra, but have so far been carried out only in a quasi-1D framework, with three atomic species (H, He and O). Here, we present 2.5D Monte Carlo radiative transfer simulations which model the emission from a non-spherical outflow, including a more comprehensive set of cosmically abundant species. While the basic trend of OXR increasing with inclination is preserved, the inherently multi-dimensional nature of photon transport through the non-spherical outflow significantly affects the emergent SEDs. Relaxing the quasi-1D approximation allows photons to preferentially escape in (polar) directions of lower optical depth, resulting in a greater variation of bolometric luminosity as a function of inclination. According to our simulations, inclination alone may not fully explain the large dynamic range of observed TDE OXRs. We also find that including metals, other than Oxygen, changes the emergent spectra significantly, resulting in stronger absorption and emission lines in the extreme ultraviolet, as well a greater variation in the OXR as a function of inclination. Whilst our results support previously proposed unified models for TDEs, they also highlight the critical importance of multi-dimensional ionization and radiative transfer.