Journal Article

Long-term optical and X-ray variability of the Seyfert galaxy Markarian 79

E. Breedt, P. Arévalo, I. M. McHardy, P. Uttley, S. G. Sergeev, T. Minezaki, Y. Yoshii, C. M. Gaskell, E. M. Cackett, K. Horne and S. Koshida

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 394, issue 1, pages 427-437
Published in print March 2009 | ISSN: 0035-8711
Published online March 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.14302.x
Long-term optical and X-ray variability of the Seyfert galaxy Markarian 79

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We present the results of concurrent X-ray and optical monitoring of the Seyfert 1 galaxy Mrk 79 over a period of more than 5 yr. We find that on short to medium time-scales (days to a few tens of days) the 2–10 keV X-ray and optical u- and V-band fluxes are significantly correlated, with a delay between the bands consistent with 0 d. We show that most of these variations may be well reproduced by a model where the short-term optical variations originate from reprocessing of X-rays by an optically thick accretion disc. The optical light curves, however, also display long time-scale variations over thousands of days, which are not present in the X-ray light curve. These optical variations must originate from an independent variability mechanism and we show that they can be produced by variations in the (geometrically) thin disc accretion rate as well as by varying reprocessed fractions through changes in the location of the X-ray corona.

Keywords: galaxies: active; galaxies: individual: Mrk 79; galaxies: Seyfert

Journal Article.  8591 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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