Models of Accretion Disks

TL;DR

This paper reviews models of accretion disks around supermassive black holes, discussing their structure, emission components, and challenges in matching theoretical predictions with observed quasar spectra.

Contribution

It provides a comprehensive overview of standard and recent accretion disk models, highlighting discrepancies and presenting examples of spectral fitting to constrain model parameters.

Findings

Discrepancies between predicted and observed quasar spectra.

Models fitted to optical-UV-X-ray data provide parameter constraints.

Discussion of emission components' roles in quasar spectra.

Abstract

An accretion flow onto a supermassive black hole is the primary process powering quasars. However, a geometry of this flow is not well constrained. Both global MHD simulations and observations suggest that there are several emission components present in the nucleus: an accretion disk, hot plasma (corona or sphere) with electrons scattering the optical and UV photons, and an outflow (wind/jet). The relative location and size of these emission components, as well as their "interplay" affect the emerging quasar spectrum. I review briefly standard accretion disk models and the recent progress, point out discrepancies between the predicted and observed spectra and discuss some issues in fitting these models to the broad-band spectral energy distribution of quasars. I present examples of models fitted simultaneously to the optical-UV-X-ray data and possible constraints on the parameters.