EDP Sciences
Free access
Volume 405, Number 3, July III 2003
Page(s) 903 - 908
Section Galactic structure and dynamics
DOI http://dx.doi.org/10.1051/0004-6361:20030586

A&A 405, 903-908 (2003)
DOI: 10.1051/0004-6361:20030586

Photometric activity of the Seyfert galaxy Markarian 6 from UBV observations in 1970-2001

V. T. Doroshenko

Crimean Laboratory of the Sternberg Astronomical Institute, University of Moscow, Russia; P/O Nauchny, 98409 Crimea, Ukraine Isaac Newton Institute of Chile, Crimean Branch
(Received 10 December 2002 /Accepted 21 March 2003)

The light curve of Mrk 6 for 1970-2002 is presented and discussed. The amplitudes of variability were 1.6 $^{\rm m}$, 1.1 $^{\rm m}$, and 0.8 $^{\rm m}$ in UBV bands, respectively. The magnitudes of the underlying galaxy in the 27.5 '' aperture were found to be $U_{\rm g}=15.82$, $B_{\rm g}=15.42$ and $V_{\rm g}=14.36$. The mean color indices of the variable component are $(U-B)_{\rm var}=-0.49$ and $(B-V)_{\rm var}=0.75$ without correction for reddening. In the time intervals from 10 days to 1300 days the structure function can be presented as a power function, $S\!F\propto\tau^b$, where $b=0.72\pm0.04$. The time where the SF for Mrk 6 reaches the upper plateau is about 3300 days. The observed SF can be interpreted by the superposition of independent flares model with the maximal duration of flares ~800 days. If these flares are located in the radiation pressure dominated region of the accretion disk, the size of this region is about 70, 330 $R_{\rm S}$, assuming the viscous parameter $\alpha$ is 0.1, 0.01, respectively. It is concluded that the optical long-term variability of Seyfert galaxies can be explained by thermal instability in the accretion disk.

Key words: galaxies: active -- galaxies: individual: Mrk 6 -- galaxies: nuclei -- galaxies: Seyfert

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© ESO 2003