Explaining changing-look AGN with state transition triggered by rapid mass accretion rate drop

Understand

We model the broadband (optical/UV and X-ray) continuum spectrum of the "changing-look" active galactic nucleus (AGN) Mrk 1018 as it fades from Seyfert 1 to 1.9 in $\sim 8$ years.

• The brightest spectrum, with Eddington ratio $L/L_{\rm Edd}\sim 0.08$, has a typical type 1 AGN continuum, with a strong "soft X-ray excess" spanning between the UV and soft X-rays.
• The dimmest spectrum, at $L/L_{\rm Edd} \sim 0.006$, is very different in shape as well as luminosity, with the soft excess dropping by much more than the hard X-rays.
• The soft X-ray excess produces most of the ionizing photons, so its dramatic drop leads to the disappearance of the broad line region, driving the "changing-look" phenomena.