Optical variability of the blazar S4 0954+658 in 2008–2012

The results of multi-color photometric and polarization observations of the blazar S4 0954+658 carried out mainly in the Astronomical Institute of St. Petersburg State University and the Central Astronomical Observatory of the Russian Academy of Sciences in 2008–2012 are analyzed. Individual variable components that are responsible for the activity are distinguished; the power-law spectrum and high degree of polarization confirm that the emission is synchrotron radiation. Modeling the observed dependences between the parameters of the polarization and intensity is used to derive parameters of both the constant and the variable components of the radiation. The observed color variability (“the brighter, the bluer”) can be explained by the superposition of a red constant component and a bluer variable component with a constant relative spectral energy distribution.