"X-ray, optical and NIR long term monitoring of AGN"

Paulina Lira
Universidad de Chile

The optical continuum emission in AGN is tought to originate directly
from the accretrion disc. Hence, understanding the optical variability
can provide key insights into the physics and dynamics of the
accretion flow. The short variability time scales and lack of optical
inter-band lags suggest that X-ray heating of the disc might drive the
observed variations. However, long term X-ray/optical monitoring of
AGN is very scarse and the results present a confusing picture. Uttley
et al. (2003) proposed that the differences can be explained as
differences in the mass and accretion rates in AGN, which define the
location of the optical emitting region in the disc and hence affects
the realtion between this and the centrally emitting X-ray
source. This also suggests that the characteristics of the NIR
emission, expected to originate in the reprocessing of the central
source emission by dust, should only follow the shorter wavelength
variations, independently of the BH mass and accretion rates, and
present a lag given by the location of the dust sublimation radius.

I will present X-ray, optical and NIR light curves for NGC3783 and
MR2251-178 over 3 years of monitoring and interprete them under the
scenario exposed above. These objects span a large range in BH
mass. Our results shed some new light on the nature of the accretion
flow and the reprocessing of the emission from the central source in
AGN.