1995A&A...298..688W

The flat-spectrum radio quasar PKS 0420-014 has been identified as a variable gamma-ray source in the 100MeV to 5GeV energy band. We studied the variations of this object in the optical frequency regime, and found pronounced flares. The highest gamma-ray flux densities were recorded during the most prominent flare in the optical range observed to date. Non-detections at gamma-ray energies coincide with low states on the optical flux. A compilation of historical data is used to construct the overall spectrum, derive broad-band spectral indices from simultaneous measurements and describe them by a model which assumes a synchrotron cut-off in the optical range. The gamma-ray emission is created by inverse Compton scattering of the radiation from hot circumnuclear dust. These photons are scattered by those electrons which are producing the synchrotron radiation of the simultaneous optical flare. Geodetic VLBI experiments are used to derive maps which clearly show superluminal motion of a knot on a curved trajectory. Both, the core component and the knot vary in flux. The optical light curve is drastically undersampled but consistent with the assumption of repeated outbursts at 13 month intervals. This may be an indication that the flares are caused by a knot of enhanced particle density propagating on a helical trajectory in a rotating jet.