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Session: Extragalactic Astronomy and Astrophysics

Name: Dr. Christos Panagiotou (MIT)
Coauthors: Kara Erin (MIT)
Papadakis Iossif (University of Crete)
Dovciak Michal (Astronomical Institute of the Academy of Science)
Kammoun Elias (IRAP, Universite de Toulouse)
Type: Oral
Title: Reproducing the UV/optical variability of AGN
Abstract:

AGN continuum reverberation mapping is based on the broadly accepted idea that the X-ray corona irradiates the accretion disk, causing a delayed UV/optical response. However, in recent years, the results of several multi-wavelength studies pointed at a discrepancy between observations and the underlying theory, detecting low X-ray/UV correlations and larger than expected interband time lags. In order to further examine the assumption of disk X-ray reprocessing, we developed a physical model to reproduce the UV/optical power spectra of AGN assuming the thermal reprocessing of the X-rays in the disk. We apply our model to a sample of sources and we found that the observed power spectra and time lags can be well explained. Expanding on this result, we show that the low X-ray/UV correlation is, in fact, expected if the corona is dynamic. This is simply due to the underlying assumptions in the definition of the cross correlation function statistic. Our results suggest that X-ray disk reprocessing accounts for the full variability properties of the observed AGN disk emission, reconciling observations with theoretical predictions; while our model offers a novel way to probe the inner region of AGN.