2001ApJ...551..172P

The Effelsberg 100 m radio telescope has been used over a period of 5.5 yr to monitor the flux densities of 40 extragalactic radio sources. In this paper we study the long-term variability characteristics over timescales of several months of the quasar PKS 0528+134 at several wavelengths. It shows that the 6 cm light curve of the source hints at a time-asymmetric behavior as could be expected from an asymmetric source structure. The wavelength dependence of the degree of variability does not meet the predictions of the interstellar scintillation theory. Furthermore, variations of the spectral indices (α⁶_2.8) follow the shock models. We conclude that the variations in PKS 0528+134 are probably intrinsic, and several intrinsic models are briefly discussed to interpret the observed variability properties.