2021MNRAS.506.4188L

The physical mechanism for triggering the changing-look phenomenon in active galactic nuclei (AGNs) is still unclear. We explore this issue based on the multiwavelength 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 a 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 ∼20 d of optical/UV behind X-ray variations in type 1.9 phase. The 5 GHz radio flux decreases by ∼20 per cent in type 1.9 phase during 2016-2017. We find that both the X-ray photon index (Γ) and the optical-to-X-ray spectral index (α_ox ) are anticorrelated with the Eddington scaled 2-10 keV X-ray luminosity (L_X/L_Edd) in the type 1.9 phase. However, the type 1 phase deviates from these two anticorrelations, which suggests that the change of broad emission lines might be regulated by the evolution of accretion disc (e.g. disappearing of the inner cold disc in the type 1.9 phase).