A Physical Model for the UV/Optical Power Spectra of AGN

0560484 - ASÚ 2023 RIV GB eng J - Journal Article
Panagiotou, C. - Papadakis, I. - Kara, E. - Kammoun, E. - Dovčiak, Michal
A Physical Model for the UV/Optical Power Spectra of AGN.
Astrophysical Journal. Roč. 935, č. 2 (2022), č. článku 93. ISSN 0004-637X. E-ISSN 1538-4357
R&D Projects: GA MŠMT(CZ) LTAUSA17095; GA ČR(CZ) GX21-06825X
Institutional support: RVO:67985815
Keywords : active galactic nuclei * X-ray active galactic nuclei * Seyfert galaxies
OECD category: Astronomy (including astrophysics,space science)
Impact factor: 4.9, year: 2022
Method of publishing: Open access

The UV/optical variability of active galactic nuclei (AGN) has long been thought to be driven by the X-ray illumination of the accretion disk. However, recent multiwavelength campaigns of nearby Seyfert galaxies seem to challenge this paradigm, with an apparent discrepancy between observations and the underlying theory. In order to further probe the connection between the UV/optical and X-ray variability in AGN, we developed a physical model to reproduce the UV/optical power spectral densities (PSDs) of AGN assuming the thermal reprocessing of the X-rays in the disk. This model offers a novel way to probe the innermost regions of AGN. We use our model to study the variability of NGC 5548, and we infer that the X-ray and UV/optical PSDs as well as the interband UV/optical time lags are all well reproduced. We also derive constraints on the source physical parameters, such as the X-ray corona height and the accretion rate. Our results suggest that X-ray disk reprocessing accounts for the full variability properties of this AGN, within the considered timescales. Using earlier data of NGC 5548, we also show that our model can reproduce its PSD in different epochs, establishing the feasibility of using PSD modeling to investigate the time evolution of a source.
Permanent Link: https://hdl.handle.net/11104/0334214