The use of different methods of determining the periods of variability of extragalactic radio sources 3C120, 3C345, OJ287 at 30 years of observations at centimeter wavelengths

The paper used data from almost 40 years of monitoring the fluxes of radio sources 3C120, 3C345, OJ287, held on the 26-meter radio telescope from the University of Michigan, at frequencies of 14.5 GHz (1974–1999) 8 GHz (1965–1999) and 4.8 GHz (1978–1999). Applied processing technique, which allows consistently identify periods of flux variability from the longest to the shortest. The main periods of long-term variability of fluxes at the source 3C120 were 11, 13 and 13.5 years, at the source 3C345 – 18, 20.5 and 24.7 years, OJ287 – 16, 17.7 and 23 years. Also, found a large number of short periods in the range of 0.8–3 years from all sources at different frequencies. For each radio allocated separate periods of activity, observed simultaneously at three frequencies. In each period of active growth phase flux are allocated, the maximum and minimum phase, as well as intermediate extrema. We show that in each period of activity changes in the flux of time shift between adjacent pairs of different frequencies differed in the various phases of activity. This source 3C120 maximum time shift, depending on the frequency was within the 0.10–1.06 years, 3C345 0.88–2.60 years and for OJ287 0.06–0.94 years.