X-ray, optical and NIR long term monitoring of AGN (Paulina Lira, DAS-U.Chile)

The optical continuum emission in AGN is tought to originate directly from the accretrion disc. Hence, understanding the optical variability could provide key insights into the physics and dynamics of the accretion flow. The short variability time scales and lack of optical inter-band lags had suggested 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. Also, until now it has been assumed that the NIR emission mostly originates in the reprocessing of the central source emission by dust. However, under certain conditions NIR emission could also be detected from the accretion disk.

I will present X-ray, optical and NIR light curves of NGC3783 and MR2251-178 over 3 and 4 years and interprete them under the scenario exposed above. These objects span a wide range in BH mass which is expected to be one of the parameters that determine the characteristic temperature profile of the disk. 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.