Magnetized Accretion Disks with Outflows for Changing-look AGNs

Abstract

Changing-look active galactic nuclei (CL-AGNs) challenge the standard accretion theory, owing to their rapid variability. Recent numerical simulations have shown that, for the sub-Eddington accretion case, the disk is magnetic pressure–dominated, thermally stable, and geometrically thicker than the standard disk. In addition, outflows were found in the simulations. Observationally, high blueshifted velocities absorption lines indicate that outflows exist in AGNs. In this work, based on the simulation results, we investigate the magnetic pressure–dominated disk, and find that the accretion timescale is significantly shorter than that of the standard thin disk. However, such a timescale is still longer than that of the CL-AGNs. Moreover, if the role of outflows is taken into account, then the accretion timescale can be shortened even further. By the detailed comparison of the theoretical accretion timescale with the observations, we propose that the magnetic pressure–dominated disk incorporating outflows can be responsible for the rapid variability of CL-AGNs.

Identifying Changing-look AGNs Using Variability Characteristics

“…Magnetically elevated accretion disks (Dexter & Begelman 2019), as well as the combination of large-scale magnetic field with radiation pressure instability (Pan et al 2021), have also been proposed as effective means to reduce the timescale. In addition, the involvement of disk outflow can aid in removing angular momentum and further reduce the timescale (Feng et al 2021a;Wada et al 2023;Wu & Gu 2023). As presented in Figure 8, these long and good-quality photometric light curves can provide a good opportunity to investigate these scenarios, especially with the advent of upcoming time domain surveys.…”