Abstract
We study the influence of propagation effects on the mean profiles of radio pulsars using the method of wave propagation in inhomogeneous media described by Kravtsov & Orlov. This approach ...allows us first to take into consideration the transition from geometrical optics to vacuum propagation, the cyclotron absorption and the wave refraction simultaneously. In addition, the non-dipole magnetic field configuration, the drift motion of plasma particles and their realistic energy distribution are taken into account. It is confirmed that, for ordinary pulsars (period P ∼ 1 s, surface magnetic field B
0 ∼ 1012 G) and typical plasma generation near the magnetic poles (multiplicity parameter λ = n
e/n
GJ ∼ 103), the polarization is formed inside the light cylinder at a distance r
esc ∼ 1000 R from the neutron star, the circular polarization being 5-20 per cent which is in agreement with observational data. A one-to-one correspondence between the signs of circular polarization and position angle (PA) derivative along the profile for both ordinary and extraordinary waves is predicted. Using numerical integration we now can model the mean profiles of radio pulsars. It is shown that the standard S-shape form of the PA swing can be realized for small enough multiplicity λ and large enough bulk Lorentz factor γ only. It is also shown that the value of the maximum derivative of PA, which is often used for determination of the angle between magnetic dipole and rotation axis, depends on the plasma parameters and could differ from the rotation vector model (RVM) prediction.
Abstract
Recent progress in very long baseline interferometry (VLBI) observations of relativistic jets outflowing from active galactic nuclei gives us direct information about jet width rjet(l) ...dependence on the distance l from the ‘central engine’. Being the missing link in previous works, this relation opens the possibility of determining the internal structure of a jet. In this article, we consider a relativistic jet submerged in an external medium with finite gas pressure Pext. Neither an external magnetic field nor an infinitely thin current sheet will be assumed. This approach allows us to construct a reasonable solution in which both the magnetic field and the flow velocity vanish at the jet boundary r = rjet. In particular, the connection between external gas pressure and internal structure of a relativistic jet is determined.
ABSTRACT
Observational studies of collimation in jets in active galactic nuclei (AGN) are a key to understanding their formation and acceleration processes. We have performed an automated search for ...jet shape transitions in a sample of 367 AGN using VLBA data at 15 and 1.4 GHz. This search has found 10 out of 29 nearby jets at redshifts z < 0.07 with a transition from a parabolic to conical shape, while the full analysed sample is dominated by distant AGN with a typical z ≈ 1. The ten AGN are UGC 00773, NGC 1052, 3C 111, 3C 120, TXS 0815−094, Mrk 180, PKS 1514+00, NGC 6251, 3C 371, and BL Lac. We conclude that the geometry transition may be a common effect in AGN jets. It can be observed only when sufficient linear resolution is obtained. Supplementing these results with previously reported shape breaks in the nearby AGN 1H 0323+342 and M87, we estimate that the break occurs at 105–106 gravitational radii from the nucleus. We suggest that the jet shape transition happens when the bulk plasma kinetic energy flux becomes equal to the Poynting energy flux, while the ambient medium pressure is assumed to be governed by Bondi accretion. In general, the break point may not coincide with the Bondi radius. The observational data support our model predictions on the jet acceleration and properties of the break point.
Laboratory plasma ejections within the plasma focus facilities (the structure of their electric currents, rotation, shock wave arising from interaction with the ambient medium) reproduce all the main ...elements of jets from young stars. On the other hand, the physical processes responsible for the launch of a plasma ejection are still not well understood, and therefore there is still no unequivocal answer to the question of how adequately the laboratory experiment reproduces the mechanism of astrophysical jet formation. In this paper, we formulated the conditions under which the similarity of physical processes can also take place in the “central engine” of a laboratory experiment leading to the launch of a plasma ejection, based on the analysis of the effects of nonideal magnetohydrodynamics.
Abstract
We propose a new method of estimating the mass of a supermassive black hole residing in the centre of an active galaxy. The active galaxy M87 offers a convenient test case for the method due ...to the existence of a large amount of observational data on the jet and ambient environment properties in the central area of the object. We suggest that the observed transition of a jet boundary shape from a parabolic to a conical form is associated with the flow transiting from the magnetically dominated regime to the energy equipartition between plasma bulk motion and magnetic field. By coupling the unique set of observations available for the jet kinematics, environment and boundary profile with our MHD modelling under assumption on the presence of a dynamically important magnetic field in the M87 jet, we estimate the central black hole mass and spin. The method leads us to believe that the M87 supermassive black hole has a mass somewhat larger than typically accepted so far.
ABSTRACT
In this paper, which is the first in a series of papers devoted to a detailed analysis of ‘the death line’ of radio pulsars, we consider a possibility of producing secondary particles at a ...sufficiently long pulsar period P. To this end, we reconsidered the potential drop necessary for secondary plasma generation in the inner gap over magnetic polar caps. Our research made it possible to refine the conditions for generating secondary plasma, such as the multiplicity of the production of secondary particles and their spatial distribution. Our research also made it possible to further quantitatively analyse the dependence of the possibility of secondary plasma generation on all parameters, including the inclination angle of the magnetic axis to the rotation axis, the polar cap size and the magnetic field geometry.
ABSTRACT
In this paper, which is the second in a series of papers, we analyse what parameters can determine the width of the radio pulsar ‘death valley’ in the P–${\dot{P}}$ diagram. Using exact ...expression for the maximum potential drop, which can be realized over magnetic polar caps and the corresponding threshold for the secondary plasma production determined in Paper I, we analyse in detail the observed distribution of pulsars taking into account all the possible parameters (radius R and moment of inertia of a neutron star Ir, high-energy tail in the γ-quanta energy distribution giving rise to secondary particles, etc.) which could broaden ‘the death line’. We show that the consistent allowance for all these effects leads to a sufficiently wide of ‘the death valley’ containing all the observed pulsars even for dipole magnetic field of a neutron star. We emphasize that the main goal of this work is to demonstrate that the original Ruderman–Sutherland idea of the death line (dipole magnetic field, vacuum gap) is in good agreement with observations. The comparison with other models is beyond the scope of this paper.
ABSTRACT
The present work is devoted to the analysis of the internal structure of relativistic jets under the condition that the velocity of the plasma flow at the jet axis vanishes. It is shown that ...in spite of the seemingly fundamental difference in the formulation of the problem at the axis, the key properties of the internal structure of such relativistic jets remain the same as for non-zero velocity along the axis. In both cases, at a sufficiently low ambient pressure, a dense core appears near the axis, the radius of which is close to the size of the light cylinder.
ABSTRACT
In this first paper from forthcoming series of works devoted to radio image of relativistic jets from active galactic nuclei the role of internal structure of a flow is discussed. We ...determine the radial profiles of all physical values for reasonable Michel magnetization parameter σM and ambient pressure Pext. Maps of Doppler boosting factor δ and observed directions of linear polarization of synchrotron emission are also constructed.
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