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

• Published in: Monthly notices of the Royal Astronomical Society Vol. 394; no. 1; pp. 427 - 437
• Main Authors: Breedt, E., Arévalo, P., McHardy, I. M., Uttley, P., Sergeev, S. G., Minezaki, T., Yoshii, Y., Gaskell, C. M., Cackett, E. M., Horne, K., Koshida, S.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 21.03.2009; Wiley-Blackwell; Oxford University Press
• Subjects: Accretion disks; Astronomy; Earth, ocean, space; Exact sciences and technology; galaxies: active; galaxies: individual: Mrk 79; galaxies: Seyfert; Stars & galaxies; X-rays; galaxies: active; galaxies: individual: Mrk 79; galaxies: Seyfert; Variability; Light curves; Accretion disks; Markarian galaxies; Time variation; Active galaxies; Seyfert galaxies; Short term variation; Models; Seyfert 1 galaxies
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2008.14302.x

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.