Analysing the transverse structure of the relativistic jets of active galactic nuclei

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Murphy, Eoin Gerard
Cawthorne, T. V.
Gabuzda, Denise
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Oxford University Press
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This paper describes a method of fitting total intensity and polarization profiles in very long baseline interferometry (VLBI) images of astrophysical jets to profiles predicted by a theoretical model. As an example, the method is used to fit profiles of the jet in the active galactic nucleus (AGN) Mrk 501 with profiles predicted by a model in which a cylindrical jet of synchrotron plasma is threaded by a magnetic field with helical and disordered components. This fitting yields model Stokes Q profiles that agree with the observed profiles to within the 1-2 sigma uncertainties; the I model and observed profiles are overall not in such good agreement, with the model I profiles being generally more symmetrical than the observed profiles. Consistent fitting results are obtained for profiles derived from 6-cm VLBI images at two distances from the core, and also for profiles obtained for different wavelengths at a single location in the VLBI jet. The most striking success of the model is its ability to reproduce the spine-sheath polarization structure observed across the jet. Using the derived viewing angle in the jet rest frame, delta' similar or equal to 83 degrees, together with a superluminal speed reported in the literature, beta(app) = 3.3, yields a solution for the viewing angle and velocity of the jet in the observer's frame, delta similar or equal to 15 degrees and beta similar or equal to 0.96. Although these results for Mrk 501 must be considered tentative, the combined analysis of polarization profiles and apparent component speeds holds promise as a means of further elucidating the magnetic field structures and other parameters of parsec-scale AGN jets.
Galaxies , Active , Jets
Murphy, E., Cawthorne, T. V. and Gabuzda, D. C. (2013) 'Analysing the transverse structure of the relativistic jets of active galactic nuclei', Monthly Notices of the Royal Astronomical Society, 430(3), pp. 1504-1515. doi: 10.1093/mnras/sts561
© 2013, the Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society