We study the entire sample of quasars detected above 100 MeV (by the EGRET instrument), on board CGRO. We find that the γ-ray luminosity correlates better with the radio luminosity than with the optical or X-ray luminosity, even if the different variability behaviour indicates different emission regions. A strong correlation is also found between the broad-band spectral indices αro, connecting the radio and the optical fluxes, and αoγ, connecting the optical and the γ-ray fluxes. The γ-ray luminosity in BLLac objects is on average much less dominant than in the other sources. With the requirement that the γ-rays do not interact with X-rays (assumed cospatial) through photon-photon collisions, we calculate the lower limit on the Doppler or beaming factor of the γ-ray emission region for a large fraction of the sources of the sample, finding that relativistic motion is required in all cases.
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Dondi et al. (1995) studied this question.