We also test the obtained magnetic flux against the observed jet power. Our aim is to compare the magnetic flux in a jet against theoretically limited flux by MAD state and to estimate the rotation rate. In this paper we make use of the brightness temperature and core shift measurements coupled with the transversal jet model to express the magnetic field magnitude and the magnetic flux contained in a blazar jet through the rotation rate of magnetic surfaces. (2014) used the magnetic field measurements to calculate the flux and to show that the total flux is in accordance with the magnetically arrested state of the sources. The magnetic field estimates is an important parameter that allows to test the theoretical models against observations. However, the measurement of radio flux itself, or, equally, the brightness temperature, can provide us with the instrument to probe the magnetic field magnitude ( Zdziarski et al., 2015 Nokhrina, 2017). The way to estimate the magnetic field amplitude through the observations is measurements of core shift effect together with several theoretical assumptions on the radiating volume properties ( Lobanov, 1998). Thus, the high-resolution radio interferometry observations provide us with data for unveiling the physical conditions at the very jet origin-in so called radio core.

The lower part of the spectrum is dominated by synchrotron radiation of relativistic plasma in a jet magnetic field. Blazar spectrum is successfully modeled by the synchrotron self-Compton model. There are observational means to evaluate the magnetic field in a jet. The state of magnetically arrested disk (MAD) ( Narayan et al., 2003 Tchekhovskoy et al., 2011 McKinney et al., 2012) sets up the limiting magnetic field that can be accreted onto a black hole basing on an assumption that in such a state the pressure of previously accreted magnetic field can affect the dynamical process of accretion itself. The Eddington magnetic field ( Beskin, 2010) sets up an upper limit on the magnetic field magnitude in the vicinity of a black hole, since it is set by equipartition of magnetic field density and the total energy density in the accreting plasma that is needed to support the Eddington luminosity. There are several theoretical ways to estimate the latter. One of the key issues of theoretical modeling of relativistic jets is determining the magnetic field magnitude. We also obtain the extremely slow rotation rates, which may be an indication that the majority of the sources considered are not in the magnetically arrested disk state. We show that the total jet power estimated through the magnetic flux is in good agreement with the observed power. The resultant expression for power depends logarithmically weakly on an unknown rotation rate. On the other hand, the flux estimate may be tested against the total jet power predicted by the electromagnetic energy extraction model. If we assume the sources are in a magnetically arrested disk state, the lower limit for the rotation rate can be obtained. The accurate account for the jet transversal structure allow us to express the magnetic flux through the observed values and an unknown rotation rate of magnetic surfaces. In this paper we address the issue of estimating the magnetic flux contained in a jet using the measurements of a core shift effect and of a brightness temperature for the jets, directed almost at the observer. In both cases the obtained magnetic field is in the radiating domain, so its direct application to the calculation of the magnetic flux needs some theoretical assumptions.

On the other hand, the magnetic field in a jet can be estimated through measurements of either the core shift effect or the brightness temperature. The magnitude of magnetic field and the magnetic flux in the vicinity of a central black hole is predicted by theoretical models. Magnetic field threading a black hole ergosphere is believed to play the key role in both driving the powerful relativistic jets observed in active galactic nuclei and extracting the rotational energy from a black hole via Blandford-Znajek process. Relativistic Astrophysics Laboratory: Basic and Applied Studies of Space Objects, School of Fundamental and Applied Physics, Moscow Institute of Physics and Technology, Dolgoprudny, Russia.

Magnetic flux