Frequency-Dependent Core Shifts in Ultracompact Quasars

Abstract

Results of a pilot project with the participation of the "Kvazar-KVO" radio interferometry array in observations carried out with the European VLBI Network are presented. The aim of the project was to conduct and analyze multi-frequency (1.7, 2.3, 5.0, 8.4 GHz) observations of the parsec-scale jets of 24 active galactic nuclei. Three observing sessions were successfully carried out in October 2008. Maps of the radio intensity distributions have been constructed in all four frequencies using phase referencing. A method for measuring the frequency-dependent shift of the position of the VLBI core by applying relative astrometry to observations of close triplets of radio sources has been developed. The fundamental possibility of detecting core shifts in ultra-compact sources for which traditional methods based on the achromatic positions of optically thin regions of the jet are not suitable is demonstrated. The conditions for successful measurement of this shift are discussed; these are determined by the closeness of the calibrator used, the effective resolution of the system, the quality of the filling of the $uv$ plane, the relative orientations of the jets in the triplets, and the brightnesses of the sources.

arXiv commentAccepted for publication in Astronomy Reports; 24 pages, 9 figures, 3 tables

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• Direction of Parsec-Scales Jets for 9220 Active Galactic Nuclei
• Testing the magnetic flux paradigm for AGN radio loudness with a radio intermediate quasar
• Time variability of the core-shift effect in the blazar 3C 454.3
• Parsec-scale properties of the peculiar gigahertz-peaked spectrum quasar 0858-279
• Opacity, variability and kinematics of AGN jets
• A millisecond pulsar position determined to 0.2 milliarcsecond precision with VLBI
• The Core-shift of Sagittarius A* as a Discriminant between Disk and Jet Emission Models with millimeter-VLBI