Frequency-Dependent Core Shifts in Ultracompact Quasars


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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.

About the authors

P. A. Voitsik

Astro Space Center, Lebedev Physical Institute

Author for correspondence.
Email: voitsik@asc.rssi.ru
Russian Federation, ul. Profsoyuznaya 84/32, Moscow, 117997

A. B. Pushkarev

Astro Space Center, Lebedev Physical Institute; Crimean Astrophysical Observatory

Email: voitsik@asc.rssi.ru
Russian Federation, ul. Profsoyuznaya 84/32, Moscow, 117997; Nauchnyi, Crimea, 298409

Yu. Yu. Kovalev

Astro Space Center, Lebedev Physical Institute; Moscow Physical Technical Institute; Max Planck Institut for Radio Astronomy

Email: voitsik@asc.rssi.ru
Russian Federation, ul. Profsoyuznaya 84/32, Moscow, 117997; Institutskii proezd 9, Dolgoprudnyi, Moscow oblast, 141700; 69 Auf dem Hügel, Bonn (Endenich), D-53121

A. V. Plavin

Astro Space Center, Lebedev Physical Institute; Moscow Physical Technical Institute

Email: voitsik@asc.rssi.ru
Russian Federation, ul. Profsoyuznaya 84/32, Moscow, 117997; Institutskii proezd 9, Dolgoprudnyi, Moscow oblast, 141700

A. P. Lobanov

Max Planck Institut for Radio Astronomy; Institute for Experimental Physics

Email: voitsik@asc.rssi.ru
Germany, 69 Auf dem Hügel, Bonn (Endenich), D-53121; Luruper Chaussee 149, Hamburg, D-22761

A. V. Ipatov

Institute of Applied Astronomy

Email: voitsik@asc.rssi.ru
Russian Federation, Kutuzovskaya nab. 10, St. Petersburg, 191187

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