Photometric activity of the Seyfert galaxy Markarian 6 from UBV observations in 19702001

The light curve of Mrk 6 for 1970-2002 is presented and discussed. The amplitudes of variability were 1.6 m, 1.1 m, and 0.8 m in UBV bands, respectively. The magnitudes of the underlying galaxy in the 27.5 ʹʹ aperture were found to be Ug= 15.82, Bg = 15.42 and Vg=14.36. The mean color indices of the variable component are (U-B)var= - 0.49 and (B-V)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, SF (proportional to)   (tau)b, where b = 0.72+- 0.04. 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(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.