Changing-look Narrow-Line Seyfert 1s?
  Two major challenges to unification schemes for active galactic nuclei (AGN)
are the existence of Narrow-Line Seyfert 1s (NLS1s) and the existence of
changing-look (CL) AGNs. AGNs can drastically change their spectral appearance
in the optical (changing their Seyfert type) and/or in the X-ray region. We
illustrate the CL phenomenon with our multi-wavelength monitoring of NGC 2617
and discuss its properties compared with NLS1s. There are few examples of CL
NLS1s and the changes are mostly only in the X-ray region. It has been proposed
that some of these could be cases of a tidal-disruption events (TDE) or
supernova events. If BLRs have a flat geometry and NLS1s are seen face-on then
we have to see CL cases only if the orientation of the BLR changes as a result
of a TDE or a close encounter of a star without a TDE. If NLS1s include both
high Eddington accretion rate and low-inclination AGNs then a significant
fraction of NLS1s could be obscured and would not be identified as NLS1s. CL
cases might happen more in such objects if dust sublimation occurs following a
strong increase in the optical luminosity.
