POLARIZATION SIGNATURES OF RELATIVISTIC MAGNETOHYDRODYNAMIC SHOCKS IN THE BLAZAR EMISSION REGION. I. FORCE-FREE HELICAL MAGNETIC FIELDS

ABSTRACT The optical radiation and polarization signatures in blazars are known to be highly variable during flaring activities. It is frequently argued that shocks are the main driver of the flaring events. However, the spectral variability modelings generally lack detailed considerations of the se...

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Bibliographic Details
Published in:The Astrophysical journal 2016-01, Vol.817 (1), p.63
Main Authors: Zhang, Haocheng, Deng, Wei, Li, Hui, Böttcher, Markus
Format: Article
Language:English
Subjects:
ASTRONOMY AND ASTROPHYSICS
Blazars
Emission
Flares
galaxies: active
galaxies: jets
gamma rays: galaxies
Magnetic fields
Magnetohydrodynamics
Optical polarization
Polarization
radiation mechanisms: non-thermal
relativistic processes
Signatures
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Summary:ABSTRACT The optical radiation and polarization signatures in blazars are known to be highly variable during flaring activities. It is frequently argued that shocks are the main driver of the flaring events. However, the spectral variability modelings generally lack detailed considerations of the self-consistent magnetic field evolution modeling; thus, so far the associated optical polarization signatures are poorly understood. We present the first simultaneous modeling of the optical radiation and polarization signatures based on 3D magnetohydrodynamic simulations of relativistic shocks in the blazar emission environment, with the simplest physical assumptions. By comparing the results with observations, we find that shocks in a weakly magnetized environment will largely lead to significant changes in the optical polarization signatures, which are seldom seen in observations. Hence an emission region with relatively strong magnetization is preferred. In such an environment, slow shocks may produce minor flares with either erratic polarization fluctuations or considerable polarization variations, depending on the parameters; fast shocks can produce major flares with smooth polarization angle rotations. In addition, the magnetic fields in both cases are observed to actively revert to the original topology after the shocks. All these features are consistent with observations. Future observations of the radiation and polarization signatures will further constrain the flaring mechanism and the blazar emission environment.
ISSN:0004-637X
1538-4357
1538-4357
DOI:10.3847/0004-637X/817/1/63