Optical and Near-IR long-term monitoring of NGC3783 and MR2251-178:
  evidence for variable near-IR emission from thin accretion discs
  We present long term near-IR light curves for two nearby AGN: NGC3783 and
MR2251-178. The near-IR data are complemented with optical photometry obtained
over the same period of time. The light curves in all bands are highly variable
and good correlations can be seen between optical and NIR variations.
Cross-correlation analysis for NGC 3783 suggests that some disc near-IR
emission is present in the J-band flux, while the H and K-bands are dominated
by emission from a torus located at the dust sublimation radius. For MR2251-178
the cross-correlation analysis and the optical-near-IR flux-flux plots suggest
that the near-IR flux is dominated by disc emission. We model the optical to
near-IR Spectral Energy Distributions (SED) of both sources and find that disc
flaring might be a necessary modification to the geometry of a thin disc in
order to explain the observations. The SED of MR2251-178 gives some indications
for the presence of NIR emission from a torus. Finally, we consider the
implications of the standard alpha disc model to explain the different origin
of the variable NIR emission in these AGN.
