High Frequency VLBI Rotation Measure of 8 AGN

Abstract

We have studied Very Long Baseline Array (VLBA) polarimetric observations of 8 sources including quasars and BL Lacs at 12, 15, 22, 24 and 43 GHz and high frequency rotation measure ($RM$) maps are presented. We find typical values for the $RM$ in the VLBI core of several thousand rad/m${}^2$, which are higher than values in the literature at lower frequencies. Assuming a dependence of the form $RM\propto {\nu }^a$, we obtain an average value of $a=3.6\pm 1.3$, which is larger than that expected by theoretical considerations. Rotation measures are detected in the jet of only two sources and we find that only 0906+430 (and possibly 1633+382) show indications of a robust gradient. We discuss the Faraday--corrected polarization properties of the sources. Our interpretation supports the presence of helical magnetic fields with new, unresolved, components affecting the intrinsic direction of polarization close to the base of the jet of some objects.

14 pages, 2 tables, 9 figures. Accepted for publication in MNRAS

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Cited by in corpus (14)

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• Broadband Radio Polarimetry and Faraday Rotation of 563 Extragalactic Radio Sources
• Transverse Faraday-Rotation Gradients Across the Jets of 15 Active Galactic Nuclei
• Parsec-scale Faraday rotation and polarization of 20 active galactic nuclei jets
• Broadband radio circular polarization spectrum of the relativistic jet in PKS B2126-158
• Revealing the Nature of Blazar Radio Cores through Multi-Frequency Polarization Observations with the Korean VLBI Network
• Ejection of Double knots from the radio core of PKS 1510--089 during the strong gamma-ray flares in 2015
• Resolving the rotation measure of the M87 jet on kilo-parsec scales
• 18-22 cm VLBA Faraday rotation studies of six AGN jets
• First Detection of 350 Micron Polarization From a Radio-loud AGN
• MOJAVE -- XXII. Brightness temperature distributions and geometric profiles along parsec-scale AGN jets
• Depolarization and Faraday effects in AGN Jets
• Kilogauss magnetic field and jet dynamics in the quasar NRAO 530
• Simulations of linear polarization of precessing AGN jets at parsec scales