On the Time Variable Rotation Measure in the Core Region of Markarian 421

Rocco Lico,Keiichi Asada,J L Gómez ,Antonio Fuentes

doi:10.3390/galaxies5040057

Abstract

In this conference contribution, we discuss and interpret the time variable rotation measure (RM) detected in the core region of the TeV blazar Markarian 421 (Mrk 421). We monitored Mrk 421 during 2011 with one observing run per month at 15, 24, and 43 GHz with the American Very Long Baseline Array. We explore the possible connection between the RM and the accretion rate, and we investigate the Faraday screen properties and its location with respect to the jet emitting region. Among the various scenarios, the jet sheath is the most promising candidate for being the main source of Faraday rotation. We interpret the RM sign reversals observed during the one-year monitoring within the context of the magnetic tower models by invoking the presence of two nested helical magnetic fields in the relativistic jet with opposite helicities, originating through the Poynting–Robertson cosmic battery effect. The net observed RM values result from the relative contribution of both inner and outer helical fields.

Highlights

The study of the polarized emission from active galactic nuclei (AGN) jets is the most powerful tool for investigating the magnetic field structure
We mainly focus on the results presented in [6] about the rotation measure (RM) values found in the core region of Markarian 421 (Mrk 421)
RM and has the dominant contribution to the observed RM. With this magnetic field configuration and the above-mentioned values for θ and γ, we find that the direction of helical field toroidal component (Bt ) does not affect the RM sign; it only affects the direction of the RM gradient transverse to the jet

Summary

Introduction

The study of the polarized emission from active galactic nuclei (AGN) jets is the most powerful tool for investigating the magnetic field structure. When a polarized wave passes through a magnetized non-relativistic plasma, the observed polarization angle is rotated with respect to the intrinsic one. This is known as the Faraday rotation effect, and we need to take it into account in order to properly characterize the source polarization properties. For the RM estimate, multi-frequency polarimetric observations with the Very Long Baseline Interferometry (VLBI) technique represent the best tool, allowing us to investigate the magnetic field configuration in the innermost regions of the AGN jets (e.g., [2,3,4,5,6,7,8])

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Results

Discussion

Conclusion