Three-dimensional hydrodynamic simulations of high-mass X-ray binaries (XRBs) point to the possibility of the formation of gas–dust disks rotating around both stars (circumbinary disks, CBDs) in such binaries. However, the observational confirmation of the presence of a CBD in an XRB remains a difficult task. The possible influence of a CBD on the X-ray variability of an XRB is estimated within the kinematic model with a precessing ring CBD. It is shown that the CBD effect can provide a secular X-ray variability of XRBs, depending on the relation between the orbital and precessional parameters of XRBs with CBDs. The fact that the presence and effect of a CBD can be recorded in long-term monitoring observations of XRBs is discussed.
We consider the interaction of hard background gamma-ray photons with energies above 100 MeV with optical and X-ray background photons to produce electron–positron pairs by taking into account the accumulation of produced positrons and the subsequent energy loss by them when interacting with the cosmic microwave background. We show that a slow component of positrons with an energy below 1 MeV arises in this case, but the total number of slow positrons is only ∼0.01-0.1% of the total number of positrons produced in this interaction.
The 30-year spectroscopic and photometric monitoring of SS433 performed at the Sternberg Astronomical Institute in combination with all of the published data since 1978 have yielded a number of results that shed light on the nature of this unique microquasar. 1. The parameters of the kinematic model for SS433 (with the exception of some jumps in the precessional phase), on average, are stable over 45 years, arguing for the model of a slaved accretion disk tracking the precession of the rotation axis of the optical star. 2. The orbit of SS433 is elliptical with an eccentricity e=0.05± 0.01 . This supports the model of a slaved accretion disk. 3. A secular evolutionary increase in the orbital period of SS433 at a rate Ṗ_orb=(1.14± 0.25)× 10^-7 s s ^-1 has been discovered. Hence it follows that the relativistic object in SS433 is a black hole with a mass of more than 8 M_⊙ . 4. It follows from the increase in the orbital period of SS433 that the semimajor axis of this binary system increases with time, preventing the formation of a common envelope in the binary. Therefore, SS433 evolves as a semidetached binary system—a powerful wind from the supercritical accretion disk stabilizes the binary system. This paper has been written using the materials of the report presented by us at the Conference ‘‘High-Energy Astrophysics Today and Tomorrow—2025’’ and is based on our more detailed paper published in UFN (Cherepashchuk et al. 2025).
We have analyzed a number of features in radio pulsars with surface magnetic fields in the range 10^9-10^10 G. In the distribution of magnetic fields for the pulsars from the ATNF catalog the sample under study corresponds to the minimum between the millisecond and normal pulsars. We provide arguments for the assumption that the central neutron stars in this sample are in binary systems and continue to spin up through the accretion of matter outflowing from the companion. More than 70% of the pulsars under study are actually members of binary systems. They must be younger than the millisecond pulsars that have reached their minimum spin period. Indeed, their mean characteristic age is a factor of 2.5 shorter than that of millisecond pulsars, while their kinematic age, which is much closer to the real one, is several million years. In this time, such pulsars could not go far from the Galactic disk, where they were born and evolved. Indeed, they are concentrated near the disk, while their height z above the Galactic plane does not exceed several tens of parsecs for most of the pulsars in the sample under study.
The paper is devoted to modeling the gravitational waves from the X-ray pulsar Her X-1. The neutron star is considered as a freely precessing ellipsoid. The gravitational wave signal is calculated in the quadrupole approximation. The h_× and h_+ polarization profiles are constructed for the precession parameters of the neutron star in Her X-1 measured in up-to-date works. The possibility of signal detection with the DECIGO telescope is assessed. The formulas for the semi-analytical modeling of the gravitational wave signal from precessing neutron stars by the method of perturbations in the small neutron star ellipticity parameter are deduced.
We present the results of our search for and detection of radio emission from the gravitational-wave event GW 190425 at a frequency of 111 MHz with the BSA LPI radio telescope. A new radio source was detected approximately at 2^∘ from the center of the maximally probable localization region of GW 190425; its coordinates (J2000.0) are α=16^h30^m± 1^m and δ=13^∘21^'± 15^' . We have constructed the light curve and estimated the peak flux density to be ≈2 Jy. The peak of the light curve occurs on day 20–30 after the trigger. We have calculated the false alarm probability for an event of this kind, P_fa=5× 10^-7 .
The primordial deuterium abundance is one of the most sensitive observational tests of the standard cosmological model and the primordial nucleosynthesis theory. In this paper we perform a systematic analysis of high-resolution spectra from the SQUAD and KODIAQ catalogs aimed at searching for absorption systems suitable for measuring the D/H ratio. We have analyzed all 767 quasar spectra from these catalogs and, as a result, detected 46 new candidate systems for estimating the deuterium abundance. We have estimated the physical parameters of the medium in the chosen objects and modeled in detail the profiles of H I, D I, and metal absorption lines by the MCMC method for five systems. In contrast to the traditional approach oriented predominantly toward the most metal-poor systems with simple kinematics, the sample spans a wider range of physical characteristics of the interstellar medium. Our preliminary estimates of the D/H ratio confirm that the proposed approach is promising and show that extending the range of conditions under study increases the reliability of cosmological estimates, making it possible to investigate the dependence of the deuterium astration on metallicity and to refine the region where this effect may be neglected.
The photon energy range 0.3–10 MeV is of special interest for studying astrophysical objects of various origins. Gamma-ray spectroscopy of lines from the decay of unstable stellar nucleosynthesis isotopes and studies of nuclear cosmic-ray interactions and electron–positron pair annihilation are based on sensitive observations in this energy range. The MeV energy range accounts for a substantial part of the emission from supernovae, pulsars, gamma-ray burst sources, and accreting black holes. Observations of gamma-ray lines will allow the properties of strongly absorbed compact relativistic stars to be studied. Measuring the spectra and polarization of nonthermal continuum gamma-ray emission is needed to find out the nature of the gamma-ray emission from binary star systems with compact companions and powerful transient sources. At present, the orbital detectors in this energy range are several orders of magnitude less sensitive than both X-ray telescopes and gamma-ray detectors in the GeV and TeV energy ranges. This is related to the peculiarities of the MeV photon detection technology. Compton scattering, which was used in the CGRO/COMPTEL telescope that had operated in its orbit until 2000, offers one of the possibilities for detecting photons of such energies. In this paper we present the concept of an orbital Compton gamma-ray telescope in the energy range 0.3–10 MeV based on the modern technologies of double-sided silicon strip detectors (Si-DSSD), which allow the telescope sensitivity to be improved significantly. We present the results of our simulations of the characteristics of such a gamma-ray telescope in both full-scale and small-sized versions and make a comparison with the characteristics of the instruments in the completed CGRO/COMPTEL (NASA) and planned COSI (NASA) missions.
Based on archival data from the MUSE (Multi Unit Spectroscopic Explorer) spectrograph of the VLT, we have selected 63 candidates for high-luminosity stars with intrinsic H α emission in the galaxies NGC 1087, NGC 1433, and NGC 1566. Based on our analysis of the spectra for the candidates and the photometry performed using the archival direct images obtained with the Hubble and James Webb Space telescopes, we have made a primary classification of all sources. The largest group comprises 28 unclassified objects with only broad Balmer hydrogen lines observed in their spectra. Thirteen more sources have been assigned to the group of unclassified objects with signatures of circumstellar envelopes, such as the Ca II triplet and/or an infrared excess. Twenty one sources have been classified as Wolf–Rayet stars or compact stellar associations including them. Four objects with Fe II, [Fe II] and/or [O I] and [Ca II] emission lines in their spectra have been classified as candidates for B[e] supergiants or yellow hypergiants. One source has been classified as a candidate for oxygen-rich supernova remnants, and one more object has shown a transient nature.
The controlled motion of a spacecraft in the vicinity of a Sun–Earth collinear libration point is studied. The spacecraft motion is described by the model of the circular restricted three-body problem. An approach to constructing the orbital spacecraft motion control laws for a long stay in the designed orbits is proposed. The approach is based on the use of a special function of phase variables and time whose value characterizes the deviation of the spacecraft trajectory from the designed orbit. The results of numerical simulations are presented.
We present the results of our numerical computations of the broadband radiation spectra forming in a layer of high-temperature ( kT_e∼ 50 keV) semitransparent (with a Thomson optical depth τ_T∼ 1-3 ) plasma with an electron density N_e∼ 10^17-10^19 cm^-3 typical for the accretion disk regions surrounding a black hole in X-ray binaries. In our computations we took into account the bremsstrahlung processes of the production (and absorption) of photons and their subsequent Comptonization. The intrinsic radiation from such a high-temperature plasma is shown to be enough to explain the X-ray spectra observed in the low (hard) state of Galactic black hole candidates and X-ray novae. No commonly assumed additional soft (with energies hν≲ 1 keV) photons to maintain Comptonization are required; moreover, their presence would lead to severe distortions of the spectrum compared to the observed one or would require a very fine tuning of plasma parameters. In the hard X-ray range the forming power-law radiation spectrum with a photon index α∼ 1.4-1.7 , which has an exponential cutoff at energies hν≳ 100 keV, exceeds considerably the bremsstrahlung flux that might be expected from such a plasma layer in the limit of an infinitely small optical depth. This is a result of the multiple inverse Compton scattering of bremsstrahlung photons. It is important that, according to our computations, the power-law radiation spectrum for such a high-temperature plasma should extend in an invariable form downward along the energy axis to the ultraviolet, optical, and infrared ranges ( hν∼ 1-3 eV). At energies hν≲ 1 eV the optical depth for bremsstrahlung absorption grows rapidly and the radiation spectrum becomes the Rayleigh–Jeans one. To explain the steeper ( α∼ 2.1-2.5 ) X-ray spectra observed from accreting black holes in their high (soft or two-component) state, it is indeed necessary that a large number of soft photons additional to the intrinsic plasma bremsstrahlung photons enter a hot cloud. Such photons could be emitted by the surface of an outer dense and cold accretion disk whose inner edge during these states characterized by a powerful soft component in the X-ray spectrum approaches the black hole maximally closely. The optical and infrared emission from systems in these states is associated precisely with the emission from the outer disk, whereas during their low state it can be produced directly in the hot central disk region bloated by instabilities. Under favorable conditions (disk size and inclination) the low-frequency emission from this region can noticeably exceed in flux and luminosity the emission from the outer cold accretion disk regions.
We researched the slow, normal, and fast coronal mass ejections (CMEs) associated with solar flares ( > M5.0 X-ray class) from December 2019 to July 2023 (44 month period) in the early rising phase of solar cycle 25. This research aims to examine the features of slow, normal, and fast CMEs along with their associated Solar Flares, Type II Bursts, SEPs, and Geomagnetic Storms. This paper highlights CME-Flare pairs by grouping them based on speed and investigating their connection to DH type II bursts, solar energetic particle occurrences, and Dst indices. The locations of flares associated with the three types of CMEs, the number of events corresponding to different flare classes, as well as the flare rise times and durations, were thoroughly studied. During the study period, we analyzed the 57 CME events and the distribution of their angular widths. Using different electron density models, the start distance, end distance, drift rate, and shock speed were analyzed in detail. Solar energetic particles (SEPs) with intensities greater than 10 pfu, generated by shock waves and the geoeffectiveness of full halo CME, were discussed. In this statistical study, we conclude that the fast CMEs are associated with longer flare durations, and stronger geoeffectiveness compared to slow and normal CMEs. They are also significant drivers of type II radio bursts, SEP events, and geomagnetic storms.
Computing the spectra of supernovae at the photospheric phase requires detailed modeling of nonequilibrium atomic level populations in a rapidly expanding envelope. We consider the fundamental problem of interpreting the observed spectra through the solution of a highly stiff system of time-dependent kinetic equations in an expanding envelope, where the characteristic time scales of atomic processes differ from the hydrodynamic time scale by many orders of magnitude. Based on the analysis of a singularly perturbed system, we introduce a heuristic rule for the selective deactivation of sparsely populated levels, reducing the dimension of the system and the computational cost without any loss of accuracy. An extremely large scatter of characteristic process time scales leads to a numerical instability that manifests itself as nonphysical negative populations and a ‘‘jump’’ to a false solution. We present a modified fourth-order Rosenbrock method supplemented by a correction procedure that guarantees the positivity of the solutions based on the works of Goldin and Kalitkin. This correction acts as a specialized step controller, automatically preventing the choice of too large integration steps that lead to an instability. The method is implemented in the LEVELS code and has been tested on the type II-P supernova SN 2018aoq. We show that the hybrid approach stably integrates a system of more than 1500 equations and allows the observed optical spectra to be satisfactorily reproduced, making it possible to refine the hydrodynamic explosion parameters based on spectroscopic data.
The conditions for filamentation in coronal magnetic loops are investigated. In such loops fairly large electric currents can exist and manifestations of current self-focusing effects are possible. For typical parameters of coronal magnetic loops filamentation is shown to arise at currents exceeding 5× 10^9 A. The characteristic thickness of the filaments and their total number are determined for typical plasma parameters and electric currents in loops. As a rule, the cross sections of the filaments have a total area smaller than the cross-sectional area of the coronal magnetic loop. For this reason, the phenomenon of filamentation leads to an increase in the total energy release from the system of filaments at the same total current that existed in the original homogeneous loop. At a typical number of filaments observed in experimental data the total energy release from the loop is shown to increase approximately by an order of magnitude. This effect vanishes at a sufficiently large number of filaments, when the total area of their cross sections almost coincides with the cross-sectional area of the loop.
Based on observations of the pulsar B0329+54 with the LPA telescope at the Pushchino Radio Astronomy Observatory, we show that the Faraday rotation of the polarization plane of the polarized part of the main pulse leads not only to the well-known frequency modulation of the signal intensity, but also to two new effects: (i) a periodic frequency modulation of the time of arrival of its peak at the antenna receiving a linearly polarized emission and (ii) a frequency–time drift of the emerging bands of signal minima and maxima in the main-pulse propagation time interval. The detection of these effects constrains the admissible schemes and mechanisms for the generation of a partially polarized emission and allows one not only to improve significantly the accuracy of determining the dispersion measure, but also to judge the relative shift of the profiles of the unpolarized and linearly polarized parts of the main pulse as well as their asymmetry and steepness for pulsars with a large rotation measure. Under certain conditions, using such effects, it is possible to obtain information about the geometry and motion of the emission sources in pulsar magnetospheres and about the rotation of the polarization plane of the main pulse, which, in particular, can reveal a shear of neutron-star magnetic field lines in the regions of generation and limiting polarization of radiation.
The prospects for testing the Einstein Equivalence Principle by measuring the gravitational time dilation effect using clocks in a distant retrograde orbit around the Moon are investigated. To obtain estimates of the accuracy that can be achieved in such an experiment, we constructed a model that accounts for the colored nature of the clock noise, as well as a possible clock frequency bias and drift. This model is applied to the case of a lunar distant retrograde orbit (a 2:1 resonance) and three types of clocks characterized by qualitatively different stability and accuracy parameters: hydrogen masers (VCH-1010 and VCH-2021), a cesium fountain clock (PHARAO), and a strontium optical clock (I-SOC). Assuming 5 years of data accumulation, the following estimates for the achievable accuracy of the experiment were obtained: 6× 10^-4 for VCH-1010, 1× 10^-5 for VCH-2021, 2× 10^-5 for PHARAO, and 3× 10^-7 for I-SOC. These estimates show that an experiment with an optical clock would significantly improve upon both the current best result ( (2-3)× 10^-5 , GREAT project) and the anticipated results of experiments on the ISS and Tiangong orbital stations. A comparison of our results with previous studies that do not account for clock drift and frequency bias is provided.
We have studied the physical parameters of a group of 15 OBA stars from which X-ray emission was detected by the SRG/eROSITA telescope. Whereas the X-ray emission from cool FGKM stars is directly produced near their surface zones—in their chromospheres and coronae—the nature of the X-ray emission from OBA stars requires a separate study in each specific case, since single OBA stars are not intrinsic X-ray sources. We have determined the main physical characteristics of the stars under study, including their effective temperature T_eff and surface gravity log g , based on the spectral energy distribution and the optical spectra obtained with the 1.5-m Russian–Turkish RTT-150 telescope. An additional analysis of the H α line profiles has allowed the possible X-ray emission mechanisms to be assessed: generation in non-stationary stellar winds, collisional processes in circumstellar envelopes, and coronal emission of hidden cool companions. As a result of the analysis, we have concluded that the X-ray emission from eight stars with typical X-ray luminosities in the range log L_X=28.5-30.0 is determined by their hidden late-type companions.
We have analyzed the kinematics of open star clusters (OSCs) with their characteristics from the new catalog of Hunt and Reffert. From 4003 OSCs younger than 200 Myr we have found the following parameters of the angular velocity of Galactic rotation: Ω_0=28.99± 0.11 km s ^-1 kpc ^-1 , Ω^'_0=-3.909± 0.026 km s ^-1 kpc ^-2 , and Ω^''_0=0.662± 0.018 km s ^-1 kpc ^-3 , where V_0=234.8± 3.0 km s ^-1 for R_0=8.1± 0.1 kpc. We have established that a periodicity in the radial OSC velocities manifests itself for clusters younger than 600 Myr, while a wave in the residual tangential velocities manifests itself only for the youngest clusters younger than 40 Myr. Based on a spectral Fourier analysis of the radial velocities of three OSC samples with mean ages of 18, 72, and 143 Myr, we have obtained the following values of the wavelength λ and the velocity perturbation amplitude f_R : λ=2.0 kpc and f_R=4.3 km s ^-1 , λ=2.2 kpc and f_R=8.2 km s ^-1 , and λ=2.1 kpc and f_R=9.6 km s ^-1 , respectively. We have established a systematic change in the positions of the wave maxima and minima in the radial OSC velocities as a function of the sample age. From our analysis of these shifts we have found the absolute value of the difference |ΔΩ| of the spiral pattern speed Ω_p and the angular velocity of Galactic rotation, |ΔΩ|=2.0± 0.5_stat± 2.3_syst km s ^-1 kpc ^-1 . On this basis, we have estimated two possible corotation radii, 8.6± 0.2 and 7.6± 0.2 kpc, suggesting that the Sun is very close to corotation.
We perform a comparative analysis of the optical flaring activity of two groups (with and without X-ray emission, according to SRG/eROSITA data) of cool FGKM stars within 30 pc of the Sun based on data from the TESS space observatory. About 4800 sources within 30 pc in the eastern Galactic hemisphere have been identified based on the Gaia DR3 catalog and correlated with the SRG/eROSITA catalog of X-ray sources. As a result, we have identified 1309 X-ray sources and 3104 sources without X-ray activity. For these sources we have searched for the light curves and the manifestations of flaring activity based on data from the TESS space observatory. We show that the group of stars with X-ray activity exhibits a much higher optical flaring activity compared to the group of stars without X-ray emission. We have measured the energies of flares for both groups of stars and constructed their energy distributions.
We consider the applicability of the classical Waldmeier rule or effect, i.e., the relationship between the amplitude of the 11-year solar cycle and the length of its rising branch (rise time), to a series of total sunspot areas. We show that the absence of a correlation revealed by some authors is associated with the influence of quasi-biennial oscillations and the choice of a smoothing method. We propose a new proxy series of yearly mean sunspot group area that is free from the quasi-biennial component and Gnevyshev gaps. For this series we have estimated the correlation coefficient between the solar cycle amplitude and the length of the rising branch, R≈ 0.8 , confirming the universality of the Waldmeier rule. Values of R up to 0.99 have been reached in the modified formulations that relate the amplitude to the maximum and mean activity growth rates, making them promising for an early prediction of the solar cycle amplitude.
