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Abstract

Radius measurements of dust tori around the central engine of luminous active galaxies open up the possibility of probing cosmological models out to redshifts beyond where supernovae can be used. Yet, the value of dust tori as standard candles is constrained by the substantial intrinsic scatter in the size-luminosity relation found for samples of AGNs. Indicated by single objects, a probable cause of this scatter is a non-trivial variation in the dust location with the luminosity of the central engine, due to sublimation events and subsequent long-term reformation of the hot dust surface radiating at near-infrared wavelengths. In this work, I developed a refined dust reverberation model allowing to measure torus sizes and additional observables characterizing the temperature state, stability, and distribution of the innermost, hot dust in AGNs. Optical to near-infrared photometric data were observed for 24 type 1 AGNs. Of these, I have analyzed the Seyfert 1 galaxies NGC 4151, Ark 120, NGC 5548, and NGC 3227. The derived inner torus radii fit very well into the established size-luminosity relation. While three objects are well-described by a standard model without sublimation, the data of one object could be fit satisfactorily only after allowing for dust sublimation events in the model.