The Eddington ratio-dependent changing look events in NGC 2992
  We present an analysis of historical multi-wavelength emission of the
Changing Look (CL) Active Galactic Nucleus (AGN) in NGC 2992, covering epochs
ranging from 1978 to 2021, as well as new X-ray and optical spectra. The galaxy
presents multiple Seyfert type transitions from type 2 to intermediate-type,
losing and regaining its H$\alpha$ BEL recurrently. In X-rays, the source shows
intrinsic variability with the absorption corrected luminosity varying by a
factor of $\sim$ 40. We rule out tidal disruption events or variable
obscuration as causes of the type transitions and show that the presence and
the flux of the broad H$\alpha$ emission line are directly correlated with the
2-10 keV X-ray luminosity (L$_{2-10}$): the component disappears at L$_{2-10}
\leq 2.6\times10^{42}$\ergcms, this value translates into an Eddington ratio
($\lambda_{\rm Edd}$) of $\sim$ 1\%. The $\lambda_{\rm Edd}$ in which the BEL
transitions occur is the same as the critical value at which there should be a
state transition between a radiatively inefficient accretion flow (RIAF) and a
thin accretion disk, such similarity suggests that the AGN is operating at the
threshold mass accretion rate between the two accretion modes. We find a
correlation between the narrow Fe K$\alpha$ flux and $\lambda_{\rm Edd}$, and
an anti-correlation between full-width at half maximum of H$\alpha$ BEL and
$\lambda_{\rm Edd}$, in agreement with theoretical predictions. Two possible
scenarios for type transitions are compatible with our results: either the
dimming of the AGN continuum, which reduces the supply of ionising photons
available to excite the gas in the Broad Line Region (BLR), or the fading of
the BLR structure itself occurs as the low accretion rate is not able to
sustain the required cloud flow rate in a disk-wind BLR model.
