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Issue A&A Volume 420, Number 1, June II 2004 Page(s) 1 - 16 Section Astrophysical processes DOI 10.1051/0004-6361:20035741

A&A 420, 1-16 (2004)
DOI: 10.1051/0004-6361:20035741

The structure and radiation spectra of illuminated accretion disks in AGN

II. Flare/spot model of X-ray variability

B. Czerny¹, A. Rózanska¹, M. Dovciak^{2, 3}, V. Karas^{2, 3} and A.-M. Dumont<sup>4

1</sup>  Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, Poland
²  Astronomical Institute, Academy of Sciences of the Czech Republic, Prague, Czech Republic
³  Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
⁴  Observatoire de Paris-Meudon, DAEC, Meudon, France

(Received 25 November 2003 / Accepted 10 February 2004)

Abstract
We discuss a model of the X-ray variability of active galactic nuclei (AGN). We consider multiple spots that originate on the surface of an accretion disk following intense irradiation by coronal flares. The spots move with the disk around the central black hole and eventually decay while new spots continuously emerge. We construct time sequences of the spectra of the spotted disk and compute the corresponding energy-dependent fractional variability amplitude. We explore the dependence on the disk inclination and other model parameters. AGN seen at higher inclination with respect to the observer, such as Seyfert 2 galaxies, are expected to have a fractional variability amplitude of the direct emission that is by a factor of a few higher than objects seen face on, such as Seyfert 1s.

Key words: radiative transfer -- accretion, accretion disks -- atomic processes -- galaxies: active -- X-rays: galaxies -- radiation mechanisms: thermal

Offprint request: A. Rózanska, agata@camk.edu.pl

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