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

Crimean Laboratory of the Sternberg Astronomical Institute, University of Moscow, Russia; P/O Nauchny, 98409 Crimea, Ukraine Isaac Newton Institute of Chile, Crimean Branch

Corresponding author: doroshen@sai.crimea.ua

Received: 10 December 2002
Accepted: 21 March 2003

Abstract

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'' aperture were found to be , and . The mean color indices of the variable component are and without correction for reddening. In the time intervals from 10 days to 1300 days the structure function can be presented as a power function, , where . 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 α 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.