  The active galactic nucleus (AGN) NGC 7213 shows a complex correlation
between the monochromatic radio luminosity $L_R$ and the 2--10 keV X-ray
luminosity $L_X$, i.e. the correlation is unusually weak with $p\sim 0$ (in the
form $L_R\propto L_X^p$) when $L_X$ is below a critical luminosity, and steep
with $p>1$ when $L_X$ is above that luminosity. Such a hybrid correlation in
individual AGNs is unexpected as it deviates from the Fundamental Plane of AGN
activity. Interestingly, a similar correlation pattern is observed in the black
hole X-ray binary H1743--322, where it has been modelled by switching between
different modes of accretion. We propose that the flat $L_R$--$L_X$ correlation
of NGC 7213 is due to the presence of a luminous hot accretion flow, an
accretion model whose radiative efficiency is sensitive to the accretion rate.
Given the low luminosity of the source, $L_X\sim 10^{-4}$ of the Eddington
luminosity, the viscosity parameter is determined to be small, $\alpha\approx
0.01$. We also modelled the broad-band spectrum from radio to $\gamma$-rays,
the time lag between the radio and X-ray light curves, and the implied size and
the Lorentz factor of the radio jet. We predict that NGC 7213 will enter into a
two-phase accretion regime when $L_X > 1.5 \times 10^{42}\, {\rm erg\,s^{-1}}$.
When this happens, we predict a softening of the X-ray spectrum with the
increasing flux and a steep radio/X-ray correlation.

High Energy Astrophysical Phenomena