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

The source OGLE-BLG-DN-0064 (hereafter OGLE64) was classified as a potential dwarf nova based on its regular outburst activity revealed by the OGLE optical survey. In this paper we investigate the X-ray and optical emissions from the source OGLE64 based on archival Chandra and Swift X-ray data and our optical observations with the 6-m BTA telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences. OGLE64 shows an X-ray luminosity (L_{X}approx 1.6times 10^{32}) erg s({}^{-1}) and a high X-ray-to-optical flux ratio (F_{X}/F_{textrm{opt}}approx 1.5) typical for accreting white dwarfs. The X-ray spectrum of OGLE64 is better fitted by the models of a power law with a photon index (Gammaapprox 1.9) and an optically thin plasma with a temperature (kTapprox 6.4) keV. The optical spectrum shows hydrogen and neutral helium emission lines in some of which a double-peaked structure is observed. An analysis of the outburst activity of OGLE64 based on data from the OGLE, ZTF, ATLAS, and ASAS-SN optical surveys has revealed superoutbursts with a characteristic supercycle (P_{textrm{super}}approx 400) days. We found no significant variability in either the X-ray or optical light curves of OGLE64 that could be associated with the change in the visibility conditions for the emitting regions at different orbital phases. Our estimates of the orbital period of the system by indirect methods show that the period probably lies in the range (P_{textrm{orb}}sim 1.5{-}3.5) h. The properties of the X-ray and optical emissions from OGLE64 lead us to conclude that the system is an SU UMa-type dwarf nova.

The spectral and photometric studies of the cataclysmic variable Gaia 19cwm (or ZTF19aamkwxk) have been performed. Based on the analysis of long-term variability, it is concluded that the object belongs to WZ Sge type stars. The light curves show eclipses recurring with an orbital period of (86.32048pm 0.00005) min, as well as an out-of-eclipse variability with a period of ({approx}6.45) min. The latter period is stable for ({sim}4) years and appears to correspond to the rotation of a magnetic white dwarf, i.e., Gaia 19cwm is an intermediate polar. The Gaia 19cwm spectra show photospheric lines of the white dwarf, and Doppler tomograms demonstrate the presence of an accretion disk and a hot spot. Analysis of the eclipse light curve gives an estimates of the white dwarf mass (M_{1}=0.66pm 0.06) (M_{odot}), the donor mass (M_{2}=0.073pm 0.015) (M_{odot}), and the orbital inclination (i=83.8^{circ}pm 1.1^{circ}). Modeling of the spectral energy distribution gives the white dwarf temperature of (T_{textrm{eff}}approx 13,000) K. The X-ray luminosity (L_{X}=(1.6pm 0.3)times 10^{31}) erg/s allows to assign Gaia 19cwm to a small group of low-luminosity intermediate polars.

Supernova 2018ibb of the PISN category, related to the dynamical instability of oxygen core in a supermassive star induced by pair-creation shows at the nebular stage strong [O III] emission lines of an uncertain origin. I propose a simple model that demonstrates a possibility of [O III] lines emission from the supernova oxygen matter ionized and heated by the ({}^{56})Co radioactive decay. The reason is pinpointed by which the [O III] line luminosity among supernovae of PISN category can vary in a broad range.

The study of primordial black holes (PBHs) and the Hawking radiation that they can generate is an important step in understanding the role of these phenomena in the cosmological evolution of the Universe. PBHs can be part of the dark matter, the seeds of supermassive black holes, and the sources of Hawking radiation, which, in contrast to the radiation from other black holes, can be observable. At the same time, under conditions of the evolution of the Universe from the Big Bang to the present day, PBHs lose most of their mass in the form of neutrino emission. This is because for black holes with (M<10^{23}) g, apart from the emission of massless particles, the emission of the lightest massive particle, the neutrino, is added. Moreover, this emission turns out to be dominant, and since only black holes with masses ({lesssim}10^{15}) g have evaporated significantly by the present time ((t_{0}=13.8) Gyr), the neutrino component dominates in the overall emission spectrum of PBHs. In this paper we present new estimates of the spectra of neutrinos emitted by PBHs of various masses, focusing attention on the low-energy ((mathbf{E}_{textrm{kin}}in[0.01{-}1]) eV) emission for the first time. As a result of our calculations, we have shown that black holes in the range of masses ([10^{9}{-}10^{11}]) g emit neutrinos with an intensity exceeding the background fluxes from known astrophysical sources in the low-energy range, while in the high-energy range the emission will be under the background without coming into conflict with observational constraints. These results open up new opportunities for the potential observation of emission from PBHs and can stimulate the development of neutrino detection technologies in the low-energy range. The observation of neutrinos in this range is one of the few possibilities to confirm the existence of Hawking radiation.

We have analyzed the time series of coordinates for 5468 radio sources obtained from geodetic VLBI observations in 1993–2024. We have identified 49 objects whose coordinates change within the range from 6 to 143 mas. We have revealed several types of astrometric instability probably associated with different astrophysical processes in active galactic nuclei. In some cases, the coordinates change rapidly over a relatively short time interval (1–3 years). These peculiarities should be taken into account while compiling the next fundamental astrometric ICRF catalogue.

We propose alternative processes of generation of positrons producing 511 keV annihilation line in the Galactic bulge by cosmic rays. Since relativistic cosmic rays produce both positrons and gamma rays and the flux of the latter is limited by observations, we consider sub-relativistic particles. Particles with energies below the threshold of charged pions production can generate positrons in two processes: direct pair production in electromagnetic interactions (ultraperipheral collisions) and by production of unstable isotopes by spallation and proton capture. Cross-sections of these processes are very small at non-relativistic energies and rapidly increase with particles velocities. Optimal protons velocities are about (0.1{-}0.3) of luminal velocity. In this velocity range, the cross-sections are high enough while gamma rays production is low. Thus, to produce positrons a special class of cosmic ray sources is necessary. These sources should produce large amount of sub-relativistic particles in the specified velocity range. We consider fast blue optical transients and stellar tidal disruptions by central black hole as these type of sources. Characteristic outflow velocities in these objects are of order of tenth of luminal velocity. If acceleration of relativistic particles in these outflows is low enough, they can produce the required amount of positrons. We also show that energy produced by stellar tidal disruptions events is large enough to produce the required amount of positrons.

We have analyzed the change in the period of the ultracompact binary system ZTF J213056.71+442046.5, a source of potentially detectable mHz gravitational waves for planned space laser interferometers. The photometric data cover a time interval of almost 6.5 years and include our own observations carried out with the RC600 telescope at the Caucasus Mountain Observatory of the Sternberg Astronomical Institute of the Moscow State University and data from the ZTF sky survey. The (O-C) diagram can be described by quadratic light elements that correspond to a rate of period decrease (dP/dt=(-2.66pm 0.62)times 10^{-12}) s s({}^{-1}). This value leads to an almost twofold increase in the expected signal-to-noise ratio for the observations of gravitational waves from this binary system with space laser interferometers.

By combining data from several X-ray telescopes (Swift/XRT, NICER, Chandra) we reconstructed a profile of the 2019 outburst of accreting X-ray pulsar 4U 1901+03 from its peak down to the return to the ‘‘low’’ state. Softening of the X-ray spectrum and disappearance of the pulsations at a later stages of the outburst tentatively indicates that the source transitioned to the ‘‘propeller’’ state at luminosity about (10^{36}) erg s({}^{-1}), which corresponds to a magnetic field strength of (Blesssim 10^{12}) G at the neutron star surface. We also investigated the fast X-ray variability that was observed during the peak of 2003 outburst. The shape of the power spectrum could be described with a broken power law, with a break frequency of 7.5 Hz. Assuming that this frequency corresponds to a viscous frequency at a magnetospheric boundary we estimated magnetic field strength as (Bapprox 7times 10^{11}) G, which is similar to the estimate obtained from observed transition to the ‘‘propeller’’ regime.

Observational manifestations of disturbances in a protoplanetary disk caused by a collision with a massive planet are studied. It is assumed that the planet moves along a parabolic trajectory that intersects the disk plane near the star. Gas-dynamic simulation is performed using the finite volume method on a long time scale. On its basis, images of the disk observed from the pole and edge-on are constructed in the infrared and submillimeter ranges. A wide range of planet orbit parameters is considered. The approach of the planet was considered both prograde and retrograde with the respect to the disk rotation. Calculations have shown that in the images of the disk seen pole-on, two spiral arms can be observed in case of the prograde fall, and one with retrograde case. In the case of observations of a disk whose plane is inclined at a small angle to the line of sight, distortions of the disk plane can be noticeable. In addition, a gas tail is extended from the disk in the direction of the planet’s motion, which can also be identified in observations.

We present new results of our photometric and spectroscopic monitoring of the WTTS star V715 Per that is located in the young cluster IC 348 and exhibits a complex pattern of variability. We show that the variability of the H(alpha) line equivalent width is modulated with the rotation period of the star and is in antiphase with its brightness variations. This serves as a confirmation of the previously proposed model for the photometric variability of V715 Per based on variable circumstellar extinction in the inner disk at the corotation radius. According to our estimates, the radical change in the pattern of variability occurred after 2010 is attributable with a high probability to changes in the rate of accretion in the system. Our new photometric data have shown the end of the long fading of the star observed in the period 2017–2023 and caused by the occultation of an extended dusty structure in the outer disk. The refined period of the low-amplitude variability component is (5.22^{textrm{d}}) and showed stability over the entire series of observations