Astronomy Letters-A Journal of Astronomy and Space Astrophysics最新文献

Transonic (with Mach number (M_{s}gtrsim 1)) motion of a pulsar relative to the external medium can help its compact pulsar wind nebula develop a double-torus X-ray morphology. The double-torus structure can reverberate as a whole under the dynamic pressure of the external flow. For a flow aligned with the symmetry axis of the nebula, the response of the double-torus is uniform in azimuth. For a misaligned flow, the leeward sides of the tori respond with some delay relative to their windward sides. The delay can cause a curious swaying in the short midsection of the leeward jet of the compact X-ray nebula. Within the framework of the relativistic magnetohydrodynamical model of a pulsar wind nebula we study the dynamics of the nebular outflows contributing to the swaying of the jet. When applied to the Vela X-ray nebula, the model allows us to naturally relate two distinct phenomena, the swaying of the bright midsection of the Vela lee jet and the reverberation of its double-torus.

Using a relativistic plasma with an isotropic monoenergetic distribution of electrons and positrons as an example, we show that in the maser regime the maximum possible amplification of synchrotron radiation at a distance of one wavelength is achieved in a medium where the magnetic energy density is of the order of the particle energy density. This ratio of the energy densities corresponds to a (Harris-type) current sheet. We have obtained an electron Lorentz factor of 350 and a magnetic field strength of 10 kG in the maser radio emission region for the Crab pulsar. Our estimate suggests that the optical and coherent radio emissions of the object originate from one synchrotron source in the form of a current sheet. The diameter of the source must exceed the light-cylinder radius approximately by a factor of 6 for the maser wave field to interact with particles in the linear regime, in particular, to keep its phase velocity higher than the speed of light in a vacuum—a necessary condition for the synchrotron instability.

We present the results of our analysis of the series of X-ray observations, photometric and spectroscopic monitoring for the ultraluminous X-ray source VII Zw 403 ULX (UGC 6456 ULX). Based on a number of indirect signs, we hypothesize that the accretor in this binary system is a neutron star. By analyzing the observed spectrum of this ULX taken during its active state within the framework of the model of a wind coming from the supercritical accretion disk, we have estimated the mass outflow rate to be ({approx}4.0times 10^{-5}M_{odot}) yr({}^{-1}).

We have performed a comparative analysis of the angles (beta) between the rotation axis and the magnetic moment in three groups of radio pulsars: sources in which only radio emission is observed, pulsars with detected X-ray emission, and radio-loud gamma-ray pulsars. For this purpose, we have calculated the values of the angle (beta) separately for objects from each group by two different methods. It has turned out that in pulsars with hard emission the mean values of this angle (28.2({}^{circ}) and 28.8({}^{circ})) are higher than those for quiet radio pulsars (12.9({}^{circ})). However, using the Kolmogorov–Smirnov test, we have shown that the revealed difference is insignificant with a high probability. Consequently, the structures of the magnetospheres in the three groups of pulsars considered do not differ significantly, while their difference is attributable to the values of the magnetic field on the light cylinder that switches on the hard non-thermal emission mechanism in pulsars with detected X-ray and/or gamma-ray emission but is not enough for this in radio pulsars without hard emission.

The pulsar J0901–4046 has a spin period (P=75.8) s and is the most slowly rotating one among the isolated radio pulsars. We have considered the influence of a small-scale magnetic field in the off-centered dipole model on the polar cap heating by the reverse positron current in the inner gap of the pulsar. We have assumed that the electron–positron pairs in the gap are created in bound states, which then are broken by thermal photons from the stellar surface.

In the fall of 2019, during the in-flight calibration phase of the SRG observatory, the onboard eROSITA and Mikhail Pavlinsky ART-XC telescopes carried out a series of observations of PG 1634+706 — one of the most luminous (an X-ray luminosity ({sim}10^{46}) erg s({}^{-1})) quasars in the Universe at (z<2). Approximately at the same dates this quasar was also observed by the XMM-Newton observatory. Although the object had already been repeatedly studied in X-rays previously, its new observations allowed its energy spectrum to be measured more accurately in the wide range 1–30 keV (in the quasar rest frame). Its spectrum can be described by a two-component model that consists of a power-law continuum with a slope (Gammaapprox 1.9) and a broadened iron emission line at an energy of about 6.4 keV. The X-ray variability of the quasar was also investigated. On time scales of the order of several hours (here and below, in the source rest frame) the X-ray luminosity does not exhibit a statistically significant variability. However, it changed noticeably from observation to observation in the fall of 2019, having increased approximately by a factor of 1.5 in 25 days. A comparison of the new SRG and XMM-Newton measurements with the previous measurements of other X-ray observatories has shown that in the entire 17-year history of observations of the quasar PG 1634+706 its X-ray luminosity has varied by no more than a factor of 2.5, while the variations on time scales of several weeks and several years are comparable in amplitude.

We have carried out a comprehensive study of the poorly investigated eclipsing polar 1RXS J184542.4(+)483134 with a short orbital period (P_{textrm{orb}}approx 79) min. An analysis of its long-term light curves points to a change in the position and sizes of the accretion spot as the accretion rate changes. Narrow and broad components, which are probably formed on the ballistic segment of the accretion stream and on the magnetic trajectory, respectively, are identified in the emission line profiles. An inversion of the line profiles from emission to absorption due to the obscuration of the accretion spot by the accretion stream is observed. Based on the eclipse duration and the radial velocities of the narrow line component, we impose constraints on the white dwarf mass, (0.49leq M_{1}/;M_{odot}leq 0.89), and the orbital inclination, (79.7^{circ}leq ileq 84.3^{circ}). An analysis of the cyclotron spectra points to the presence of two accretion spots with magnetic field strengths (B_{1}=28.4^{+0.1}_{-0.2}) MG and (B_{2}=30{-}36) MG. The main spot has a complex structure that apparently has a dense core and a less dense periphery emitting a spectrum with cyclotron harmonics. Polarization observations reveal a circular polarization sign reversal during the orbital period and an anticorrelation of the polarization with the brightness of the polar. Our modeling of polarization observations using the simple model of an accreting white dwarf shows that the polarization properties can be interpreted in terms of two-pole accretion with different optical depths of the accretion spots ((tau_{1}/tau_{2}sim 10)). An analysis of the Swift/XRT observations points to a predominance of bremsstrahlung in the X-ray radiation from the system.

Evolutionary sequences of AGB stars with initial masses on the main sequence (M_{textrm{ZAMS}}=1.5;M_{odot}), (2;M_{odot}), and (3;M_{odot}) were computed for the initial metallicity (Z=0.014). Selected models of evolutionary sequences with envelopes under thermal equilibrium were used as initial conditions for calculation of nonlinear stellar pulsations. The hydrodynamic models of each evolutionary sequence are shown to concentrate along the continuous line in the period–radius and period–luminosity diagrams. The theoretical period–radius and period–luminosity relations differ from one another for different main–sequence star masses because the stellar luminosity of AGB stars depends on the degenerate carbon core mass which increases with increasing (M_{textrm{ZAMS}}). In hydrodynamic models of evolutionary sequences (M_{textrm{ZAMS}}=2) and (3;M_{odot}) the periods of the first overtone pulsators are (86leqPileq 123textrm{d}) and (174leqPileq 204textrm{d}), whereas all models of the evolutionary sequence (M_{textrm{ZAMS}}=1.5;M_{odot}) oscillate in the fundamental mode. Fairly regular radial oscillations exist in stars with pulsation periods (Pilesssim 500) d. In models with longer periods the amplitude rapidly increases with increasing (Pi) and oscillations become irregular.

We present the results of our long-term photometric and spectroscopic monitoring with the 1.5-m telescope RTT-150 for the optical counterpart of the high-mass X-ray binary IGR J21343+4738 discovered in 2002 by the INTEGRAL space X-ray observatory. The X-ray source was also repeatedly detected by the telescopes of the SRG observatory during the all-sky surveys in the period 2019–2021. We have investigated the spectroscopic and photometric variabilities of the optical counterpart, a Be star, caused by physical processes in the equatorial disk. The evolution of the equatorial disk parameters over a long time interval of 16 years has been analyzed.

A method for estimating the spatial period of energy release in solar flares is proposed to analyze the present-day satellite observations of arcades of flare coronal loops. The method is based on the application of a Fourier analysis to the difference images of flare arcades in the far ultraviolet. The operation of the method is demonstrated with the observations of the Bastille Day flare from the TRACE spacecraft in the 171 Å channel. The mean spatial period of energy release in the Bastille Day flare determined by the proposed method is 5–8 Mm, in good agreement with the scenario for the development of thermal instability of the preflare current layer in solar flares.