paper

Magnetic field strength and spectral distribution of six parsec-scale active galactic nuclei jets

arXiv:0907.5211 · doi:10.1111/j.1365-2966.2009.15428.x

Abstract

We use observations of six "blazars" with the Very Long Baseline Array (VLBA), at eight frequencies (4.6, 5.1, 7.9, 8.9, 12.9, 15.4, 22.2, 43.1 GHz), to investigate the frequency-dependent position of their VLBI cores ("core-shift") and their overall jet spectral distribution. By cross-correlating the optically thin jet emission, we are able to accurately align the multi-frequency images of three of the jets (1418+546, 2007+777, 2200+420), whose core-shifts and spectra we find consistent with the equipartition regime of the Blandford & Konigl conical jet model, where the position of the radio core from the base of the jet follows . For the jet of 0954+658, we align the higher frequency images using our lower frequency measurements assuming equipartition in the radio core from 4.6-43 GHz. The jet emission of the other two sources in our sample (1156+295, 1749+096) is too sparse for our alignment technique to work. Using our measured core-shifts, we calculate equipartition magnetic field strengths of the order of 10's to 100's of mG in the radio cores of these four AGN from 4.6-43 GHz. Extrapolating our results back to the accretion disk and black hole jet-launching distances, we find magnetic field strengths consistent with those expected from theoretical models of magnetically powered jets.

To match published version in MNRAS. Equation 5 corrected for typesetting error and references updated

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