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THE STUDY OF A MAGNETIC FIELD STRUCTURE IN
BLAZAR JETS BY OPTICAL PHOTOPOLARIMETRIC DATA
Yu.S. Efimov 1 , E.Yu. Vovk 2
1 RSI ``Crimean Astrophysical Observatory'', Nauchny, Crimea, 98409, Ukraine
2 National State University, Kiev, 01033, Ukraine
Yuri.Efimov@mail.ru
There are no direct methods to measure magnetic field intensity in sources of synchrotron
radiation. Usually estimations of magnetic field intensity are obtained from the Faraday
rotation measure in radio region with additional data about a path length and an electron
density. Besides the Faraday rotation of polarization plane there are observational param­
eters which are connected directly with the intensity of magnetic field and its structure:
a polarization degree and a spectral index. Both these parameters can be obtained from
optical observations. On the other hand, various theoretical models connect magnetic field
intensity with polarization degree.
From two polarimetric modes observed in blazars: circular and linear, the last one is rather
large (from 1% to 40%) and can be detected easily in contrast to the circular polarization
which is very small (fraction of percentage). In its turn, the linear polarization is directly
connected with spectral index. So, the comparison of theoretical predictions from vari­
ous models of magnetic field with observed dependencies between polarization degrees and
spectral indices allows to significantly confine an uncertainty of the magnetic field intensity
estimations. The first such attempt had been made about 30 years ago by Nordsieck (1976).
Moreover, such a comparison allows to follow the variations of the magnetic field intensity
from observed variations of polarization degree and spectral index.
In this report we present a result of such comparison for two well­known blazars 3C 66A
and OJ 287. It was shown that in both sources the decrease of polarization and spectral
index indicate: an increasing disorder of magnetic fields of relativistic jets.
References
Nordsieck K.H.: ApJ, 1976, 209, 653.