Long-term and multi-wavelength evolution of a changing-look AGN Mrk 1018

TL;DR

This study investigates the long-term, multi-wavelength spectral and flux variations of the changing-look AGN Mrk 1018, revealing complex emission behavior and potential links to accretion disk evolution during different phases.

Contribution

It provides the first detailed multi-wavelength analysis of Mrk 1018's changing-look phenomenon, highlighting the role of accretion disk changes in spectral state transitions.

Findings

Optical and X-ray emissions decay rapidly during 2010--2015.

A ~20-day lag of optical/UV behind X-ray variations in type 1.9 phase.

Radio flux decreases by ~20% during 2016--2017.

Abstract

The physical mechanism for triggering the changing-look phenomenon in active galactic nuclei (AGNs) is still unclear. We explore this issue based on the multi-wavelength spectral and flux variations for a changing-look AGN Mrk~1018 with long-term observations in the X-ray, optical/ultraviolet(UV), and radio bands. Both the optical and the X-ray emission experience rapid decay in changing-look phase during 2010--2015, where a re-flare appears in the optical/UV and X-ray bands. We find a time lag of $\sim 20 $ days of optical/UV behind X-ray variations in type 1.9 phase. The 5 GHz radio flux decreases by $\sim 20$\% in type 1.9 phase during 2016--2017. We find both X-ray photon index ($\Gamma$) and the optical-to-X-ray spectral index (\alphaox\,) are anti-correlated with the Eddington scaled 2--10~keV X-ray luminosity ($L_\mathrm{X}/L_\mathrm{Edd}$) in the type 1.9 phase. However, the type 1 phase deviates from these two anti-correlations, which suggests that the change of broad emission lines might be regulated by the evolution of accretion disk (e.g., disappearing of the inner cold disk in the type 1.9 phase).