Journal Article

The parsec-scale distributions of intensity, linear polarization and Faraday rotation in the core and jet of Mrk 501 at 8.4–1.6 GHz

S. M. Croke, S. P. O'Sullivan and D. C. Gabuzda

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 402, issue 1, pages 259-270
Published in print February 2010 | ISSN: 0035-8711
Published online February 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.15923.x
The parsec-scale distributions of intensity, linear polarization and Faraday rotation in the core and jet of Mrk 501 at 8.4–1.6 GHz

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Previous very long baseline interferometry (VLBI) observations of the nearby (z = 0.0337) active galactic nucleus (AGN) Mrk 501 have revealed a complex total-intensity structure with an approximately 90° misalignment between the jet orientations on parsec and kiloparsec scales. The jet displays a ‘spine’ of magnetic field orthogonal to the jet surrounded by a ‘sheath’ of magnetic field aligned with the jet. Mrk 501 is also one of a handful of AGN that are regularly detected at TeV energies, indicating the presence of high-energy phenomena in the core. However, multi-epoch analyses of the VLBI total-intensity structure have yielded only very modest apparent speeds for features in the VLBI jet. We investigate the total-intensity and linear-polarization structures of the parsec- to decaparsec-scale jet of Mrk 501 using VLBA observations at 8.4, 5, 2.2 and 1.6 GHz. The rotation-measure distribution displays the presence of a Faraday rotation gradient across an extended stretch of the jet, providing new evidence for a helical magnetic field associated with the jet of this AGN. The position of the radio core from the base of the jet follows the law rcore(ν) ∝ν−1.1±0.2, consistent with the compact inner jet region being in equipartition. Hence, we estimate a magnetic field strength of ∼40 mG at a distance of 1 pc.

Keywords: galaxies: active; galaxies: jets; galaxies: magnetic fields

Journal Article.  7858 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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