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Paper: Compact Structures in the Central Engines of Active Galactic Nuclei
Volume: 299, High Energy Blazar Astronomy
Page: 245
Authors: Kovalev, Y.Y.
Abstract: We have used visibility data obtained with the VLBA at 15 GHz to examine most compact structures in 160 flat spectrum extragalactic radio sources. With projected baselines out to 440 million wavelengths we are able to study source structure on angular scales as small as 0.12 mas. This data is comparable with space VLBI data from VSOP obtained on longer baselines but at longer wavelengths and with lower accuracy. For about 40% of the sources, at least at one epoch, more than a half of the flux density is unresolved on the longest baselines. These objects may have dimensions less than 0.12 mas. The most variable sources tend to have the most compact structure. Typical lower limits to the brightness temperature are in the range of 1011 to 1012 K, but extends up to 1013 K in apparent excess of the inverse Compton limit of stationary synchrotron sources. Longer baselines, such as will be available in future space VLBI missions, are needed to study the most compact high brightness temperature regions in these sources. The fringe visibility of the γ-ray loud AGN is more variable than for γ-ray quiet AGN. This supports models with a common emission mechanism at radio and γ-ray wavelengths.
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