Radiative Emission Mechanisms of Tidal Disruption Events

TL;DR

This paper reviews how different physical processes in tidal disruption events produce observable radiation across multiple wavelengths, emphasizing the roles of rapid circularization, debris streams, shocks, and outflows.

Contribution

It provides a comprehensive analysis of the radiative mechanisms in tidal disruption events, considering both rapid circularization and eccentric debris streams, and links observational features to physical models.

Findings

Optical/UV emission can originate from reprocessing layers and outflows.

Soft X-ray emission depends on debris circularization and shock heating.

Radio signals arise from debris interaction and jet activity.

Abstract

We describe how the various outcomes of stellar tidal disruption give rise to observable radiation. We separately consider the cases where gas circularizes rapidly into an accretion disc, as well as the case when shocked debris streams provide the observable emission without having fully circularized. For the rapid circularization case, we describe how outflows, absorption by reprocessing layers, and Comptonization can cause the observed radiation to depart from that of a bare disc, possibly giving rise to the observed optical/UV emission along with soft X-rays from the disc. If, instead, most of the debris follows highly eccentric orbits for a significant time, many properties of the observed optical/UV emission can be explained by the scale of those eccentric orbits and the shocks embedded in the debris flow near orbital apocenter. In this picture, soft X-ray emission at early times results from the smaller amount of debris mass deflected into a compact accretion disc by weak shocks near the stellar pericenter. A general proposal for the near-constancy of the ultraviolet/optical color temperatures is provided, by linking it to incomplete thermalization of radiation in the atmosphere of the emitting region. We also briefly discuss the radio signals from the interaction of unbound debris and jets with the black hole environment.