A. M. Kutkin, K. V. Sokolovsky, M. M. Lisakov, Y. Y. Kovalev, T. Savolainen, P. A. Voytsik, A. P. Lobanov
Opacity-driven shift of the apparent VLBI core position with frequency (the "core shift" effect) is a promising tool to probe physical conditions in innermost parts of AGN radio jets. We present the first detailed investigation of the core shift effect in the brightest gamma-ray blazar 3C 454.3 using multiple techniques: direct core position and size measurements with simultaneous 4.6-43 GHz VLBA observations and time lag analysis of 4.8-37 GHz radio lightcurves obtained with the 26-m UMRAO, 22-m CrAO, and 14-m Metsahovi radio telescopes in 2007-2009. The remarkable agreement found between the results obtained with different techniques supports the standard Konigl model as an appropriate description of jet physics in the VLBI core region. The distance of the core from the jet origin, the core size, and the lightcurve time lag all depend on the observing frequency (nu) as ~nu^{-1/k}. We find the value of the coefficient k to be in the range k=(0.6-0.8), consistent with the synchrotron self-absorption being the dominating opacity mechanism in the jet. If jet propagates in a pressure gradient environment, the derived value of k suggest that the jet of 3C 454.3 is expanding and accelerating in the region of its cm-band core. Assuming equipartition, we estimate the magnetic field strength at 1 pc from the jet origin to be B(1pc)~0.4 G, it is scaling with distance r as B=0.4(r/1pc)^-0.8 G. The total kinetic power of the jet, assuming its electron/positron composition, is about ~10^44 erg/s. An electron/proton jet would be about two thousand times more powerful.
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http://arxiv.org/abs/1307.4100
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