Broad-band Radio Spectra Variability of 550 AGN in 1997-2001

Results are presented of long-term monitoring at the radio telescope RATAN-600 and a model interpretation of instantaneous 1-22GHz spectra at six frequencies for a sample of 550 compact extragalactic radio sources. The sources are selected from the Preston et al. (1985) VLBI survey and are located in the declination range from -30° to +43°. Dependence of the index of variability on frequency is analysed for different subsamples. Factors of flux density variations range from 1 to 15. A typical behaviour of spectra evolution during strong radio outbursts in various objects is recognised suggesting a common physical nature of the variability. Invoking VLBI observations in spectra-structure analysis, we find that usually more than 70% of the total emission is coming from the mas scale at frequencies higher than 5GHz. The observed variability can be explained in the model with a relativistic jet of parsec scale in the longitudinal magnetic field or in the shock-in-jet model.