Modeling changing-look (CL) AGN phenomenon in 1D using accretion disk instabilities

TL;DR

This paper models the rapid luminosity and spectral changes in Changing-Look AGN using a 1D accretion disk model with instabilities driven by radiation pressure, incorporating corona and hot inner flows.

Contribution

It introduces a 1D accretion disk model with magnetic fields, corona, and hot inner flow to explain CL AGN variability on short timescales.

Findings

Model reproduces observed variability amplitudes and timescales.

Disk instabilities driven by radiation pressure can cause spectral type changes.

Inclusion of corona and hot flows enhances model realism.

Abstract

Apart from regular, low-level stochastic variability, some AGN occasionally show exceptionally large changes in the luminosity, spectral shape, and/or X-ray absorption. The most notable are the changes of the spectral type when the source classified as a Seyfert 1 becomes a Seyfert 2 galaxy or vice versa. Thus a name was coined of 'Changing-Look AGN' (CL AGN). The origin of this phenomenon is still unknown, but for most of the sources, there are strong arguments in favor of the intrinsic changes. Understanding the nature of such rapid changes is a challenge to the models of black hole accretion flows since the timescales of the changes are much shorter than the standard disk viscous timescales. We aim to model the CL AGN phenomenon assuming that the underlying mechanism is the time-dependent evolution of a black hole accretion disk unstable due to the dominant radiation pressure. We use a 1-dimensional, vertically integrated disk model, but we allow for the presence of the hot coronal layer above the disk and the presence of the inner purely hot flow. We focus on the variability timescales and amplitudes, which can be regulated by the action of large-scale magnetic fields, the description of the disk-corona coupling, and the presence of an inner optically thin flow, like Advection-Dominated Accretion Flow (ADAF). We compare model predictions for the accretion disk around black hole mass 10$^7$M$_{\odot}$.