Multi-wavelenth monitoring of the changing-look AGN NGC 2617 during
  state changes
  Optical and near-infrared photometry, optical spectroscopy, and soft X-ray
and UV monitoring of the changing-look active galactic nucleus NGC 2617 show
that it continues to have the appearance of a type-1 Seyfert galaxy. An optical
light curve for 2010$-$2017 indicates that the change of type probably occurred
between 2010 October and 2012 February and was not related to the brightening
in 2013. In 2016 and 2017 NGC 2617 brightened again to a level of activity
close to that in 2013 April. However, in 2017 from the end of the March to end
of July 2017 it was in very low level and starting to change back to a Seyfert
1.8. We find variations in all passbands and in both the intensities and
profiles of the broad Balmer lines. A new displaced emission peak has appeared
in H$\beta$. X-ray variations are well correlated with UV$-$optical variability
and possibly lead by $\sim$ 2$-$3 d. The $K$ band lags the $J$ band by about
21.5 $\pm$ 2.5 d and lags the combined $B + J$ bands by $\sim$ 25 d. $J$ lags
$B$ by $\sim$ 3 d. This could be because $J$-band variability arises
predominantly from the outer part of the accretion disc, while $K$-band
variability is dominated by thermal re-emission by dust. We propose that
spectral-type changes are a result of increasing central luminosity causing
sublimation of the innermost dust in the hollow bi-conical outflow. We briefly
discuss various other possible reasons that might explain the dramatic changes
in NGC 2617.
