arXiv subjects

A. Yu. Istomin

Publications and source records attributed to A. Yu. Istomin.

6 recordsLinked to original sources

arXiv2026

Synchrotron radiation in nonuniform magnetic field

The distortion of the spectrum of synchrotron radiation received by a distant observer due to magnetic field inhomogeneity is discussed. It is shown that for single-particle radiation, a noticeable difference in the integrated spectrum from the case of a uniform magnetic field occurs only for observation times significantly exceeding the observer's departure from the beam pattern, and only for subrelativistic particles, when the radiation arrives from regions with significantly different magnetic fields during the observation time. For shorter observation times, field inhomogeneity leads only to small-scale distortions (smaller or comparable in frequency to the gyrofrequency) and does not manifest itself in the averaged spectrum. For the case of a particle ensemble, which is of interest for astrophysical applications, the difference in the integrated spectrum becomes negligible.

astro-ph.HE↗

arXiv2026

Magnetic field and plasma number density from radio and millimeter core measurements in AGN jets

Understanding the mechanism for launching relativistic jets in active galactic nuclei relies upon measuring the magnetic field strength and emitting plasma number density, tracing their evolution along the jet, and determining the relation between their rest frame energy densities. This can be achieved using measurements of the size and brightness temperature of the compact region at the jet base (the ``core'') obtained with very long baseline interferometry (VLBI) across frequencies from 2 to 230~GHz. We develop a framework for independently estimating the magnetic field B* and the emitting plasma number density N* as functions of the jet width $d$, using multifrequency VLBI observations of the core size and brightness temperature. We apply the standard model of self-absorbed synchrotron emission, assuming power-law dependencies of the jet Doppler factor, Lorentz factor, magnetic field strength, and plasma density on the jet width. For an arbitrary jet boundary shape, we derive the dependencies B*(d) and N*(d), and explore a possible relation between the rest frame energy densities of the magnetic field and the emitting plasma. Analysis of core widths and brightness temperatures measured at multiple frequencies points to the possible presence of a magnetic flux decay and effective plasma acceleration within the observed cores at least in some sources of the sample.

astro-ph.HE↗

arXiv2025

Data from FAST and MeerKAT surveys as a test of radio pulsar physics

The data from the FAST and MeerKAT surveys has significantly increased the number of radio pulsars for which the polarization characteristics of their mean profiles have been determined in detail. This has allowed us to confirm earlier conclusions both about the nature of propagation of two orthogonal modes in the pulsar magnetospheres and about the mechanism of particle production in neutron star polar regions and their evolutionary features. We can now say with even greater confidence that mean profiles formed by the O-mode are significantly wider than those formed by the X-mode. Moreover, the observations confirm the validity of the classical Ruderman-Sutherland vacuum model of particle generation, as well as the evolution of the inclination angles of the magnetic axis to the rotation one in the direction of $90^{\circ}$.

astro-ph.HE↗

arXiv2025

Acceleration Potential and Density Profile of Secondary Plasma in the Magnetosphere of Orthogonal Pulsars

A new method for determining the accelerating potential above the polar caps of radio pulsars with an arbitrary inclination angle of the magnetic axis to the rotation axis has been proposed. The approach has been based on the concept of a vacuum gap, the height and shape of the upper boundary of which are found self-consistently together with the solution of the corresponding Poisson equation. In turn, information about the accelerating potential has made it possible to determine the transverse profiles of the secondary plasma density. It has also been shown that the effect of inverse Compton scattering on the considered processes is insignificant.

astro-ph.HE↗

arXiv2023

On the triple pulsar profiles generated by ordinary mode

A detailed study of the refraction of an ordinary wave in the magnetosphere of radio pulsars was carried out. For this, a consistent theory of the generation of secondary particles was constructed, which essentially takes into account the dependence of the number density and the energy spectrum of secondary particles on the distance from the magnetic axis. This made it possible to determine with high accuracy the refraction of the ordinary O-mode in the central region of the outflowing plasma, which makes it possible to explain the central peak of three-humped mean radio profiles. As shown by detailed numerical calculations, in most cases it is possible to reproduce quite well the observed mean profiles of radio pulsars.

astro-ph.HE↗

arXiv2022

Pulsar death line revisited -- II. 'The death valley'

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 realised 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 $I_{\rm r}$, 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.

astro-ph.HE↗