Spectropolarimetry of the changing-look active galactic nucleus Mrk 1018
  We have obtained new spectropolarimetric observations at visible wavelengths
of the changing-look active galactic nucleus (AGN) Mrk 1018. The AGN direct
spectrum shows an extremely weak continuum with faint broad H$\beta$ and
H$\alpha$ emission lines. Both lines can be fit with a single very broad
emission line component of full width at half maximum FWHM $\simeq$ 7200 km
s$^{-1}$, with no evidence of the additional 3000 km s$^{-1}$-wide component
that was previously detected. While this is in agreement with line formation in
a Keplerian disk, the line profile variability suggests that the broad emission
line region is likely more complex. The continuum polarization of Mrk 1018 is
low; it is not higher in the current faint state compared to the past bright
state, confirming that dust obscuration is not the mechanism at the origin of
the change of look. The polarization profile of the H$\alpha$ line is
asymmetric with no rotation of the polarization angle, which possibly reveals
line formation in a polar outflow. Alternatively, the polarization profile may
be the consequence of a time delay between the direct and the polarized light.
Interestingly, the polarization signatures predicted for broad lines emitted
around supermassive binary black holes are not observed.
