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O. M. Ulyanov

Publications and source records attributed to O. M. Ulyanov.

10 recordsLinked to original sources
arXiv2026

The UTR-2 decametre pulsar and transient survey I. Transient detection

Context. This paper presents a detailed description of the Decametre Pulsar and Transient Survey of the Northern Sky that was carried out in 2012-2017 using the world's largest radio telescope at decametre wavelengths - UTR-2 in Ukraine. This extensive survey covers the northern sky from declination -10 to +80 deg , with a temporal resolution of 8 ms, and explores dispersion measures up to 30 pc/cc. Aims. The major advantage of the decametre wavelength range is a comparatively wide band, in which the dispersive delay due to the interstellar plasma reaches hundreds of seconds, giving us the opportunity to determine the dispersion measure with a very high accuracy. This enables us to discover new transients, while avoiding data contamination from numerous weak signals of a different nature. Methods. The drift-scan survey in 5-beam mode of UTR-2 was carried out at night time. To cover the entire sky along the right ascension, the duration of the sessions was more than 12 hours at a time close to the autumn and spring equinoxes (to obtain the same conditions for the interference situation). 90 degrees along the declination were covered by five beams in 40 days (each equinox). Results. We discovered 380 individual transient signals with dispersion measures significantly differ from those of known sources. We determined the parameters of each single transient signal. We show that they cannot be explained by ionospheric scintillations. Repeated observations have shown that some detected transient signals are repetitive and are thus likely to originate from pulsars or rotating radio transients. Key words. Stars: neutron - pulsars: general - Methods: data analysis - Methods: observational - Astronomical databases: Surveys

astro-ph.GA↗
arXiv2021

Dual-frequency single-pulse study of PSR B0950+08

PSR B0950+08 is a bright non-recycled pulsar whose single-pulse fluence variability is reportedly large. Based on observations at two widely separated frequencies, 55 MHz (NenuFAR) and 1.4 GHz (Westerbork Synthesis Radio Telescope), we review the properties of these single pulses. We conclude that they are more similar to ordinary pulses of radio emission than to a special kind of short and bright Giant Pulses, observed from only a handful of pulsars. We argue that temporal variation of properties of interstellar medium along the line of sight to this nearby pulsar, namely the fluctuating size of decorrelation bandwidth of diffractive scintillation makes important contribution to observed single-pulse fluence variability. We further present interesting structures in the low-frequency single-pulse spectra that resemble the "sad trombones" seen in Fast Radio Bursts (FRBs); although for PSR B0950+08 the upward frequency drift is also routinely present. We explain these spectral features with radius-to-frequency mapping, similar to the model developed by Wang et al. (2019) for FRBs. Finally, we speculate that microsecond-scale fluence variability of the general pulsar population remains poorly known, and that its further study may bring important clues about the nature of FRBs.

astro-ph.HE↗
arXiv2015

Detection of the fine structure of the pulsar J0953+0755 radio emission in the decametre wave range

In this paper the anomalous intense pulse of the PSR J0953+0755 was studied in decametre wavelength range. For this pulse two scales of fine structure were discovered. The long-scale structure consists of four components, where the visible dispersion measures of even and odd components are different. The obtained time-scale of the short fine structure is 1 ms. The difference in visible dispersion measure can be caused by propagation of two normal modes of the pulsar radiation and irregularities of electron concentration in the space near the neutron star like upper layers of magnetosphere and pulsar wind.

astro-ph.HE↗
arXiv2014

Polarization Sounding of Pulsar Magnetosphere (Part I)

In a cycle of papers, starting with the present one, a fundamental possibility of the polarization sounding of a pulsar magnetosphere using pulsar self-radiation as a test signal will be considered. The main idea of such a sounding is based on the fact that in some models of pulsar magnetosphere the emission frequency depends on the height of its origin above the pulsar surface. For this purpose it is needed to study the dependence of such a parameter as the rotation measure on frequency and pulse phase. We expect that it is possible to register the rotation measure dependence on the central observing frequency and/or the pulse phase during the observations at widely spaced frequencies in the same conditions. The reliable registration of this dependence will result in resolving of the pulsar magnetosphere in depth. It is preferably to carry out the polarization researches in the observational mode of the individual pulses. In this part of the work the model of polarized pulsed radio emission and the model of weakly anisotropic propagation medium are considered. In future articles we will show how to determine the polarization parameters of pulsar radiation with the highest precision in presence of different types of recorders on the receiving side. The specifics of polarization observations at decameter wavelengths will be considered. The algorithms for solving the inverse problem for different types of receivers and the variable conductivity of the underlying surface will be developed.

astro-ph.GA↗
arXiv2013

Investigation of the Earth Ionosphere using the Radio Emission of Pulsars

The investigation of the Earth ionosphere both in a quiet and a disturbed states is still desirable. Despite recent progress in its modeling and in estimating the electron concentration along the line of sight by GPS signals, the impact of the disturbed ionosphere and magnetic field on the wave propagation still remains not sufficiently understood. This is due to lack of information on the polarization of GPS signals, and due to poorly conditioned models of the ionosphere at high altitudes and strong perturbations. In this article we consider a possibility of using the data of pulsar radio emission, along with the traditional GPS system data, for the vertical and oblique sounding of the ionosphere. This approach also allows to monitor parameters of the propagation medium, such as the dispersion measure and the rotation measure using changes of the polarization between pulses. By using a selected pulsar constellation it is possible to increase the number of directions in which parameters of the ionosphere and the magnetic field can be estimated.

astro-ph.EP↗
arXiv2012

Some evolutionary aspects of the binary stellar systems containing neutron star

The obvious lack of the binary stellar systems that contain neutron stars (NS) is observed at present. Partly it is caused by the fact that it is very difficult to detect neutron star in a binary system if this relativistic component does not manifest itself as a radio pulsar. Among 1879 pulsars that are listed in the ATNF pulsar catalogue, only 141 pulsars are known to be the companions in binary systems. Only 81 objects having median mass estimation of more than 0.2 $M_{\odot}$ constitute the binary systems with pulsars. Nevertheless, such systems should be much more numerous and their investigation is of the great interest because thier structure and evolution can certainly help in our understanding of many unique properties that are seen in some stars.

astro-ph.SR↗
arXiv2012

Origin of pulsar pulse fine structure

We give a new numerical model of pulsar pulse radiation through the interstellar medium (ISM) considering the propagation effects. It explains the deficit of a scattering measure at the decameter range of frequencies that leads to the possibility of detecting the pulsar pulse fine structure. The results of numerical simulation confirm that the fine structure may be detected at low frequencies and this is qualitatively agreed with the observational data.

astro-ph.GA↗
arXiv2012

Polarization sounding of pulsar magnetosphere

The possibility of a polarization sounding of the pulsar magnetosphere is examined, using intrinsic pulsar emission as a probe signal, for modern radio telescopes operating in the meter and decameter wavelength range. Different models of the pulsar magnetosphere at altitudes higher than a radius of critical polarization are used. The propagation medium besides magnetosphere is described by the stratified model, in which each layer has its own density of free electrons and vector of magnetic induction, as well as the spatial and temporal fluctuation scales of these parameters. The frequency dependence of the polarization parameters of the pulsar radio emission, obtained in the broad band for a selected pulse phase, will enable a sounding deep into the pulsar magnetosphere.

astro-ph.GA↗
arXiv2007

On the possible nature of Bp-Ap Stars: an application to HD101065 and HR465

We have proposed the new explanation of some magnetic chemically peculiar (MCP) stars anomalies, which is based on assumption that such stars can be the close binary systems with a secondary component being neutron star. Within this hypothesis one can naturally explain the main anomalous features of MCP stars: first of all, an existence of the short-lived radioactive isotopes detected in some stars (like Przybylski's star and HR465), and some others peculiarities (e.g. the behavior of CU Vir in radio range, the phenomenon of the roAp stars).

astro-ph↗