Search

We compare the total flux density variations and the VLBI structural variations in a sample of 27 gamma-ray blazars. We find that all the radio variations are due to shocks; the flux of the underlying jet remains constant. A large fraction of the shocks grow and fade within the innermost 0.1 mas, appearing only as ‘core flares’. Comparisons with the EGRET data show that gamma-ray flares must come from the shocks, not from the jet. At the time of an EGRET flare, the shock is typically already over a parsec downstream from the radio core, beyond the accretion disk and/or the broad line region (BLR) photon fields. Thus, present models for gamma-ray production are inadequate, since they typically model the gamma-ray inverse Compton flux as coming from the jet, with significant disk or BLR external Compton components.

A sample of 15 bright AGN has been observed at 22 GHz with two epoch global VLBI observations. The sample consists of all sources in the complete 2 Jy catalogue of Valtaoja et al. (1992) previously unobserved at 22 GHz VLBI. We have begun to investigate how much structural information can be derived just from total flux density (TFD) monitoring and how to use total flux density observations to complement space VLBI observations. As an example we present Doppler boosting factors derived in four different methods.