2004MNRAS.348.1379C

About 20 years of radio observations of the BL Lac object GC 0109+224 (S2 0109+22, RGB J0112+227) in five bands (from 4.8 to 37 GHz) are presented and analysed together with optical data. Over the past 10 years this blazar has exhibited enhanced activity. There is only weak correlation between radio and optical flare delays, usually protracted on longer time-scales in the radio with respect to the optical. In some cases no radio flare counterpart was observed for the optical outbursts. The radio variability, characterized by peak superposition, shows hints of some characteristic time-scales (around the 3-4 yr), and a fluctuation mode between the flickering and the shot noise. The reconstructed spectral energy distribution, poorly monitored at high energies, is preliminarily parametrized with a synchrotron-self-Compton description. The smooth synchrotron continuum, peaked in the near-infrared-optical bands, strengthens the hypothesis that this source could be an intermediate blazar. Moreover, the intense flux in millimetre bands, and the optical and X-ray brightness, might suggest a possible detectable γ-ray emission.