Radio Observations of Gamma-ray Blazars

Starting in 1991 we have performed a regular monitoring of EGRET sources with the Effelsberg 100-m telescope and the IRAM 30-m at Pico Veleta. In comparison with data on a sample of flat-spectrum quasars which have not been seen by EGRET we search for correlations of any kind in the behaviour of FSRQ's in the radio and gamma-ray regime. While there is no radio-to-gamma-ray luminosity correlation for these sources, it seems that gamma-ray high states coincide with increased activity in the radio regime with a strong tendency that gamma-ray outbursts precede radio outbursts. The gamma-ray spectra seem to harden with increasing flux level. We will first discuss PKS 0528+134, the most luminous γ-ray source known besides γ-ray bursts. 0528+134 exhibits superluminal motion with β app ≃ 4.4 and indications for even higher values (Pohl et al. 1995). Superluminal motion was expected since given the variability time scales of a day, the redshift of z=2.07 and the γ-ray flux in the OSSE range, strong Doppler boosting is required to satisfy the compactness limit and the Elliot-Shapiro relation (McNaron-Brown et al. 1995). It has been noted that the expulsion of new VLBI components may coincide with γ-ray outbursts (Pohl et al. 1996). In Fig.1 we show the radio light curve of 0528+134 in comparison to its γ-ray state for the period 1991 to 1995. The source was quiet in the radio regime between 1985 and 1991 (Zhang et al. 1994). The following conclusion can be drawn: 0528+134 has been very bright in γ-rays either when it was weak in radio or a few months before a mm outburst. It was at medium γ-ray level at the time of the brightest ever-recorded radio outburst, at the end of 1995. Though the γ-ray high states seem to precede the radio outbursts, which is also supported by backextrapolation of the position of VLBI knots, there is no simple one-to-one relation. The analysis of individual sources is mainly hampered by the limited coverage of the γ-ray light curve and the problem that many sources 1