arXiv subjects

A. V. Dementyev

Publications and source records attributed to A. V. Dementyev.

3 recordsLinked to original sources

arXiv2026

Basic geometric and kinematic features of the Standard Cosmological Model

We present a brief history of the construction of models of the universe, followed by calculations of quantitative characteristics of basic geometric and kinematic properties of the Standard Cosmological Model ($Λ$CDM). Using the Friedmann equations of uniform space, we derive equations characterizing a $Λ$CDM model that describes a universe corresponding to current observational data. The equations take into account the effects of radiation and ultra-relativistic neutrinos. It is shown that the universe at very early and late stages can be described to sufficient accuracy by simple formulas. Certain important moments of cosmic evolution are determined: the times when densities of the gravitational components of the universe become equal, when they contribute equally to the gravitational force, when the accelerating expansion of space begins, and several others. The dependences of different distances on redshift and the scale factor of space are derived. The distance to the sphere that expands with the speed of light (the Hubble distance), and its current and future acceleration, are found. Concepts of a horizon, second inflation, and second horizon are discussed. We consider the remote future of the universe and the opportunity, in principle, of connection with extraterrestrial civilizations.

gr-qc↗

arXiv2020

Multiwavelength behaviour of the blazar 3C279: decade-long study from $γ$-ray to radio

We report the results of decade-long (2008-2018) $γ$-ray to 1 GHz radio monitoring of the blazar 3C 279, including GASP/WEBT, $\it{Fermi}$ and $\it{Swift}$ data, as well as polarimetric and spectroscopic data. The X-ray and $γ$-ray light curves correlate well, with no delay > 3 hours, implying general co-spatiality of the emission regions. The $γ$-ray-optical flux-flux relation changes with activity state, ranging from a linear to a more complex dependence. The behaviour of the Stokes parameters at optical and radio wavelengths, including 43 GHz VLBA images, supports either a predominantly helical magnetic field or motion of the radiating plasma along a spiral path. Apparent speeds of emission knots range from 10 to 37c, with the highest values requiring bulk Lorentz factors close to those needed to explain $γ$-ray variability on very short time scales. The Mg II emission line flux in the `blue' and `red' wings correlates with the optical synchrotron continuum flux density, possibly providing a variable source of seed photons for inverse Compton scattering. In the radio bands we find progressive delays of the most prominent light curve maxima with decreasing frequency, as expected from the frequency dependence of the $τ=1$ surface of synchrotron self-absorption. The global maximum in the 86 GHz light curve becomes less prominent at lower frequencies, while a local maximum, appearing in 2014, strengthens toward decreasing frequencies, becoming pronounced at $\sim5$ GHz. These tendencies suggest different Doppler boosting of stratified radio-emitting zones in the jet.

astro-ph.HE↗

arXiv2014

Specific Features of Reflection of Radiation of a Compact Source Rotating about its Axis

Reprocessing of X-ray pulsar radiation by the atmosphere of a companion in a binary system may result in reflected pulse radiation with a period of the pulses equal to the period of the pulsar under suitable conditions. In this paper the influence of the rotation of the source - the pulsar - about its axis on the parameters of thus reflected pulses is investigated. The binary system is modeled by the spherical reflective screen and the compact source uniformly rotating about its axis; the beam pattern (BP) of the source periodically runs over the surface of the screen. Irradiation of the screen by the pulses infinitely narrow in time and by the rectangular pulses is considered. In this model parameters of the pulses reflected in some directions are calculated. The main conclusion provided by the consideration of this model is that the properties of reflected pulses - their profile, and the moments of reaching the observer - substantially depend on the correlation between the light speed and the speed of the BP passing over the companion surface. The possibility of applying of the obtained results to the known X-ray accretion-powered pulsars and rotation-powered pulsars in binary systems is examined.

astro-ph.HE↗