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

Here we present the results of a numerical study of the main reactions that determine the methyl formate abundance under conditions of a low-mass protostellar object with both normal and enhanced cosmic-ray ionization rates. The estimations of the contribution that dust chemistry has on the gas-phase methyl formate abundance are made. The impact of the transition from the prestellar to protostellar phases on the methyl-formate chemistry is studied as well.

The results of a study of the short gamma-ray burst GRB 231115A in the X-ray and gamma-ray ranges are presented, based on data from the INTEGRAL and Fermi space observatories. The source of the burst is localized by the IBIS/ISGRI telescope of INTEGRAL observatory with an accuracy of ({leq}1.!!^{prime}5), it is located in the Cigar Galaxy (M 82). Early follow-up observations of the burst localization region were carried out in the optical range with the 36-cm telescope of the ISON-Kitab observatory and the 70-cm telescope AS-32 of the Abastumani Astrophysical Observatory. The optical emission has not been detected. The proximity of the host galaxy ((D_{L}simeq 3.5) Mpc) significantly limits energetics of the event ((E_{textrm{iso}} sim 10^{45}) erg) and allows us to interpret the burst as a giant flare of a previously unknown soft gamma repeater (SGR) which is an extreme manifestation of the activity of a highly magnetized neutron star (magnetar). This conclusion is confirmed by the energy spectrum atypically hard for cosmological gamma-ray bursts, as well as the absence of optical afterglow and gravitational wave signal, which should have been detected in the LIGO/Virgo/KAGRA experiments if the burst was caused by a merger of binary neutron stars. The location of the burst in the (E_{p,i}{-}E_{textrm{iso}}) and (T_{90,i}{-}EH) diagrams also suggests that GRB 231115A was a magnetar giant flare. This is the first well-localized giant flare of an extragalactic SGR.

We present the results of the infrared photometric observations in the (JHKLM) bands and infrared spectroscopic observations in the range 1–2.5 (mu)m for the carbon Mira star T Dra performed from 2019 to 2023. An analysis of the photometric observations shows the presence of both pulsational brightness fluctuations with an amplitude falling from (1.2^{m}) in the (J) band to (0.84^{m}) in the (L) and (M) bands and a linear trend in the mean brightness with a value of (0.0007^{m}/d) in the (J) band. In the infrared spectrum of T Dra we have identified the absorption bands of C({}_{2})H({}_{2}), HCN, CN, CO, and C({}_{2}) molecules. The depth of the absorption band at 1.53 (mu)m has been found to depend on the star’s brightness. We show that the CO (lambda 2.29) (mu)m bands have a high contrast, suggesting their formation not in the stellar atmosphere but in the circumstellar dust envelope. We present the spectral energy distribution of T Dra in a wide spectral range from which the bolometric fluxes at maximum and minimum brightness have been estimated: (4.8times 10^{-10}) and (2.5times 10^{-10}) W m({}^{-2}), respectively. For the distance to T Dra of 944 pc they correspond to the star’s luminosity at maximum brightness (L_{textrm{max}}approx 13,300;L_{odot}) and at minimum brightness (L_{textrm{min}}approx 6900;L_{odot}). We have modeled the radiative transfer in the circumstellar envelope of T Dra and estimated the parameters of the star and the envelope: (T_{textrm{eff}}=2400) K, (R_{*}=670R_{odot}), (R_{textrm{in}}=5{-}6) AU, (R_{textrm{out}}sim 50,000) AU, (tau_{V}=3.5), (M_{textrm{dust}}=4{-}8times 10^{-5};M_{odot}), and (dM/dtsim 1.5times 10^{-6}) (M_{odot}) yr({}^{-1}).

We present the results of our study of the influence of stellar activity on the efficiency of the plasma radio emission generation mechanism and the properties of this emission in the atmospheres of exoplanets with a weak magnetic field. The plasma generation mechanism can be efficiently realized in the case where the Langmuir frequency exceeds the electron gyrofrequency, and the electron cyclotron maser is inefficient. This mechanism, which depends significantly on plasma parameters, suggests the generation of plasma (quasi-static) waves by energetic electrons followed by their conversion into electromagnetic radiation. The stellar wind, depending on its intensity, can modify significantly the plasmasphere of an exoplanet and change its parameters. Using the interaction of the exoplanet HD 189733b with a stellar wind of various intensities from the central star as an example, we show that the plasma mechanism can be realized at any stellar wind intensity, only the requirements for the parameters of the plasma mechanism change. In particular, the plasma wave energy density needed to generate a radio flux accessible to detection by modern radio-astronomical means changes, and its frequency range changes. The latter will allow the detected radio emission to be used as an indicator of the activity of the parent star.

The flute instability at the inner edge of a thin diamagnetic accretion disk is analyzed. The magnetic field configuration model from Aly (1980) is used. We have analyzed a modified dispersion relation for the flute instability that takes into account the Keplerian disk rotation. We have derived the inner radius of the accretion disk within our analysis of the flute instability. We show that the inner radius does not differ from the Alfvén radius for spherical accretion to within a dimensionless coefficient, with the proportionality coefficient depending only on the turbulence alpha parameter and the relative disk thickness ((h/r)).

Superbursts of neutron stars are rare but powerful events explained by the explosive burning of carbon in the deep layers of the outer envelope of the star. In this paper we perform a simulation of superbursts and propose a simple method for describing the neutrino stage of their cooling, as well as a method for describing the evolution of the burst energy on a scale of several months. We note a universal relation for the temperature distribution in the burnt layer at its neutrino cooling stage, as well as the unification of bolometric light curves and neutrino heat loss rates for deep and powerful bursts. We point out the possibility of long-term retention of the burst energy in the star’s envelope. The results can be useful for interpretation of superburst observations.

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.