Multiepoch Very Long Baseline Array observations of EGRET-detected quasars and BL Lacertae objects: Connection between superluminal ejections and gamma-ray flares in blazars

We examine the coincidence of times of high gamma -ray flux and ejections of superluminal components from the core in EGRET blazars based on a Very Long Baseline Array (VLBA) monitoring program at 22 and 43 GHz from 1993 November to 1997 July. In 23 cases of gamma -ray flares for which sufficient VLBA data exist, 10 of the flares (in eight objects) fall within 1 sigma uncertainties of the extrapolated epoch of zero separation from the core of a superluminal radio component. In each of two sources (0528 + 134 and 1730-130), two successive gamma -ray flares were followed by the appearance of new superluminal components. We carried out statistical simulations that show that if the number of coincidences is greater than or equal to 10, the radio and gamma -ray events are associated with each other at greater than 99.999% confidence. Our analysis of the observed behavior, including variability of the polarized radio flux, of the sources before, during, and after the gamma -ray flares suggests that the gamma -ray events occur in the superluminal radio knots. This implies that the gamma -ray flares are caused by inverse Compton scattering by relativistic electrons in the parsec-scale regions of the jet rather than closer to the central engine.