F-GAMMA: variability Doppler factors of blazars from multiwavelength monitoring

Recent population studies have shown that variability Doppler factors can describe blazars as a population adequately. We use the flux-density variations found within the extensive radio multiwavelength data sets of the F-GAMMA programme, a total of 10 frequencies from 2.64 up to 142.33 GHz, in order to estimate the variability Doppler factors for 58 gamma-ray bright sources, for 20 of which no variability Doppler factor has been estimated before. We employ specifically designed algorithms in order to obtain a model for each flare at each frequency. We then identify each event and track its evolution through all the available frequencies for each source. This approach allows us to distinguish significant events producing flares from stochastic variability in blazar jets. It also allows us to constrain effectively the variability brightness temperature and hence the variability Doppler factor, as well as error estimates. Our method can produce the most accurate (16 per cent error, on average) estimates in the literature to date.