  We recently discovered that the active galactic nucleus (AGN) of Mrk 1018 has
changed optical type again after 30 years as a type 1 AGN. Here we combine
Chandra, NuStar, Swift, Hubble Space Telescope and ground-based observations to
explore the cause of this change. The 2-10keV flux declines by a factor of ~8
between 2010 and 2016. We show with our X-ray observation that this is not
caused by varying neutral hydrogen absorption along the line-of-sight up to the
Compton-thick level. The optical-UV spectral energy distributions are well fit
with a standard geometrically thin optically thick accretion disc model that
seems to obey the expected $L\sim T^4$ relation. It confirms that a decline in
accretion disc luminosity is the primary origin for the type change. We detect
a new narrow-line absorber in Lya blue-shifted by ~700km/s with respect to the
systemic velocity of the galaxy. This new Lya absorber could be evidence for
the onset of an outflow or a companion black hole with associated gas that
could be related to the accretion rate change. However, the low column density
of the absorber means that it is not the direct cause for Mrk 1018's
changing-look nature.
