Back to Volume
Paper: Fine-Scale Structure of Blazars
Volume: 350, Blazar Variability Workshop II: Entering the GLAST Era
Page: 145
Authors: Kovalev, Y.Y.
Abstract: We have used interferometer fringe visibility data obtained with the VLBA at 15 GHz to examine the compact structure in 250 flat-spectrum extragalactic radio sources. For about 60% of the sources, we have at least one observation in which the VLBA core component appears unresolved (generally smaller than 0.05 mas) in one direction, usually transverse to the direction into which the jet extends. BL Lac objects are on average more compact than quasars, while active galaxies are on average less compact. Intra-Day Variable (IDV) sources typically have a more compact, more core-dominated structure on sub-milliarcsecond scales than non-IDV sources, and sources with a greater amplitude of intra-day variations tend to have a greater unresolved VLBA flux density. The objects known to be GeV gamma-ray loud appear to have a more compact VLBA structure than the other sources in our sample. This suggests that the mechanisms for the production of gamma-ray emission and for the generation of compact radio synchrotron emitting features are related. The brightness temperature estimates and lower limits for the cores in our sample typically range between 1011 and 1013 K, but they extend up to 5 × 1013 K, apparently in excess of the equipartition brightness temperature, or the inverse Compton limit for stationary synchrotron sources. The largest component speeds are observed in radio sources with high observed brightness temperatures, as would be expected from relativistic beaming.
Back to Volume