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1.
A. M. Cherepashchuk V. F. Esipov A. V. Dodin V. V. Davydov A. A. Belinskii 《Astronomy Reports》2018,62(11):747-763
Spectroscopic monitoring of SS 433 was performed during the 11 years between 2007 and 2017. Shifts of the moving Hα emission lines are analyzed and corresponding radial velocity curves plotted. All published spectroscopic data on SS 433 are used to search for secular variations of the parameters of the kinematic model. Deviations of the model parameters from their mean values are observed during relatively short time intervals (several years), but no secular changes have been detected. The presence of a component varying periodically with the orbital period is confirmed for the velocity variations for the matter in the relativistic jets, possibly indicating that the orbit of SS 433 is slightly elliptical. The stability of the parameters of the kinematic model testifies that a model with a slaved accretion disk that follows the precession of the optical star’s rotation axis is very suitable for the supercritical accretion disk in the SS 433 system. 相似文献
2.
It is shown that small glitches in the rotation period of the pulsar B1822-09 can be explained by changes in the shape of the neutron star when the shape becomes inconsistent with the rotation axis, i.e., when the symmetry axis does not coincide with the instantaneous rotation axis. Due to variations of the angle between the rotation axis and the instantaneous dipole axis due to the decreasing momentum, the angle α between the rotation axis and the symmetry axis differs from zero. As a result of mechanical stress that develops in the neutron-star crust, this angle reaches its maximum value α ≈ 2 × 10?4, then returns to zero. This change in the shape of the neutron star is observed as a slow glitch in the frequency of the pulsar’s rotation. 相似文献
3.
Between 1994 and 2006, we obtained uniform spectroscopic observations of SS 433 in the region of Hα. We determined Doppler shifts of the moving emission lines, Hα + and Hα ?, and studied various irregularities in the profiles for the moving emission lines. The total number of Doppler shifts measured in these 13 years is 488 for Hα ? and 389 for Hα +. We have also used published data to study possible long-term variations of the SS 433 system, based on 755 Doppler shifts for Hα ? and 630 for Hα + obtained over 28 years. We have derived improved kinematic model parameters for the precessing relativistic jets of S S 433 using five-and eight-parameter models. On average, the precession period was stable during the 28 years of observations (60 precession cycles), at 162.250d ± 0.003d. Phase jumps of the precession period and random variations of its length with amplitudes of ≈6% and ≈1%, respectively, were observed, but no secular changes in the precession period were detected. The nutation period, P nut = 6.2876d ± 0.00035d, and its phase were stable during 28 years (more than 1600 nutation cycles). We find no secular variations of the nutation cycle. The ejection speed of the relativistic jets, v, was, on average, constant during the 28 years, β = v/c = 0.2561 ± 0.0157. No secular variation of β is detected. In general, S S 433 demonstrates remarkably stable long-term characteristics of its precession and nutation, as well as of the central “engine” near the relativistic object that collimates the plasma in the jets and accelerates it to v = 0.2561c. Our results support a model with a “slaved” accretion disk in S S 433, which follows the precession of the optical star’s rotation axis. 相似文献
4.
It is shown that the observed width of the emission profile W 10 and the maximum derivative C of the polarization position angle for the mean profile of a pulsar can be used to calculate the ratio n of the emission-cone radius ?? to the minimum distance between the line of sight and the center of this cone fairly accurately. Estimates of n obtained earlier by eye based on the shape of the emission profiles are close to these more accurate values for pulsars from a catalog at a frequency near 1 GHz. Values of n are calculated for several dozen pulsars using data at 10 and 20 cm. In the standard model, the ratio of n at two frequencies is equal to the ratio of the squares of the distances from the center of the neutron star to the emission levels at the two frequencies. Statistical dependences of the profile width on the pulsar period for these wavelengths and a model assuming emission at the local plasma frequency are used to determine the absolute values of these distances. These estimates display good consistency and yield distances to the emission levels of the order of several tens of neutron-star radii. The calculations take into account possible variation of the dimensions of the polar cap associated with the inclination of the emission cone to the rotational axis of the pulsar; i.e., the influence of the angle ?? between the magnetic moment and rotational axis of the neutron star. Values of ?? calculated earlier for the pulsar sample considered are used for this analysis. 相似文献
5.
Observations of the X-ray pulsar 4U 2206+54 obtrained over 15 years show that its period, which is now 5555 ± 9 s, is increasing dramatically. This behavior is difficult to explain using traditional scenarios for the spin evolution of compact stars. The observed spin-down rate of the neutron star in 4U 2206+54 is in good agreement with the value expected in a magnetic-accretion scenario, taking into account that, under certain conditions, the magnetic field of the accretion stream can affect the geometry and type of flow. The neutron star in this case accretes material from a dense gaseous slab with small angular momentum, which is kept in equilibrium by the magnetic field of the flow itself. A magnetic-accretion scenario can be realized in 4U 2206+54 if the magnetic-field strength at the surface of the optical counterpart to the neutron star is higher than 70 G. The magnetic field at the surface of the neutron star is 4 × 1012 G in this scenario, in agreement with estimates based on an analysis of X-ray spectra of the pulsar. 相似文献
6.
The spin evolution of X-ray pulsars in high-mass X-ray binaries is discussed under various assumptions about the geometry and physical parameters of the accretion flow. The torque applied to the neutron star by the accretion flow and the equilibrium periods of the pulsars are estimated. It is shown that the observed spin evolution of the pulsars can be explained in a scenario in which the neutron star accretes material from a magnetized stellar wind. 相似文献
7.
I. F. Malov 《Astronomy Reports》2014,58(3):139-144
Previously developed methods for estimating the angle β between the spin axis of a neutron star and its magnetic moment together with observational data for anomalous X-ray pulsars (AXPs) indicate that these objects are nearly aligned rotators, and that the drift model can be applied to them. The magnetospheres of aligned rotators are appreciably more extended than in pulsars with large values of β. With such extents for the magnetosphere, the conditions for the generation of transverse waves via the cyclotron instability are satisfied. The expected spectrum of the resulting radiation is very steep (its spectral index is α > 3), consistent with the observed radio spectra of known AXPs (α > 2). A large magnetosphere also favors the appearance of appreciable pitch angles for relativistic electrons, and therefore the generation of synchrotron emission. The maximum of this emission falls in the microwave range. This mechanism provides appreciable fluxes at frequencies of tens of gigahertz and can explain the observed enhanced AXP radiation in this range. 相似文献
8.
We explore the possibility of explaining Anomalous X-ray Pulsars (AXPs) and Soft Gammaray Repeaters (SGRs) in a scenario with fall-back magnetic accretion onto a young isolated neutron star. The X-ray emission of the pulsar in this case originates due to the accretion of matter onto the surface of the neutron star from a magnetic slab surrounding its magnetosphere. The spin-down rate of the neutron star expected in this picture is close to the observed value. We show that such neutron stars are relatively young and are going through the transition from the propeller state to the accretor state. The pulsar’s activity in gamma-rays is connected with its relative youth, and is enabled by energy stored in a non-equilibrium layer located in the crust of the low-mass neutron star. This energy can be released due to the mixing of matter in the neutron star crust with super heavy nuclei approaching its surface and becoming unstable. The fission of nuclei in the low-density region initiates chain reactions leading to a nuclear explosion. Outbursts are probably triggered by instability developing in the region where the matter accreted by the neutron star accumulates in the magnetic polar regions. 相似文献
9.
10.
Self-consistent modeling of a protostar and protostellar disk is carried out for early stages of their evolution. The accretion rate at distances of sevral astronomical units from the protostar is appreciably variable, which is reflected in the protostar’s luminosity. The amplitude of the variations in the accretion rate and luminosity grows together with the sampling period, as a consequence of the nature of gravitationally unstable protostellar disks. A comparison of model luminosity variations with those derived from observations of nearby sites of star formation shows that the model variations are appreciably lower than the observed values for sampling periods of less than 10 years, indicating the presence of additional sources of variability on small dynamical distances from the protostar. 相似文献
11.
The accretion of neutral gas (hydrogen and helium) onto a neutron star is studied. The gas is gravitationally captured into the magnetosphere of the star, where it is ionized by thermal radiation from the stellar surface and accelerated by the electric field at the light cylinder and in a tube of open magnetic lines. Particles accelerated at light cylinder generate gamma-ray, some particles move to the star and heat its polar regions, resulting in the emission of X-rays. Our calculations of the model parameters of the X-ray and gamma-ray radiation indicate that the radiation intensities should be sufficient to be observed. 相似文献
12.
It is shown that cyclotron radiation by electrons near the surface of a neutron star with a magnetic field of ～1012 G can easily provide the observed quiescent radiation of magnetars (Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters). Pulsed emission is generated by the synchrotron mechanism at the periphery of the magnetosphere. Short-time-scale cataclysms on the neutron star could lead to flares of gamma-ray radiation with powers exceeding the power of the X-ray emission by a factor of 2γ2, where γ is the Lorentz factor of the radiating particles. It is shown that an electron cyclotron line with an energy of roughly 1 MeV should be generated in the magnetar model. The detection of this line would serve as confirmation of the correctness of this model. 相似文献
13.
We have analyzed a many-year homogeneous series of spectroscopic data for the star T Tau N. Our optical observations of hydrogen
lines and the Hand K lines of CaII have revealed periodic variations of the emission spectrum with a period of 33 ± 1.5 days.
The detected period is also observed in IUE spectrograms in the ultraviolet. Variations of the polarization of the star’s
light also agree with the derived period. Our results suggest the possible presence of a comet-like extended object orbiting
T Tau N. 相似文献
14.
N. A. Kudryashova 《Astronomy Reports》2004,48(2):108-111
We have computed the dynamical evolution of homogeneous, spherical gaseous condensations in the atmosphere of a Wolf-Rayet star. The physical conditions in the condensations vary substantially in the course of their motion in the stellar wind, which should result in variations in the observed spectrum of the star. The condensations also move at velocities of up to 1000 km/s relative to the surrounding stellar wind. Variations of the physical conditions in these condensations should be taken into account in models of the stellar winds of Wolf-Rayet stars. 相似文献
15.
Astronomy Reports - Regular variations of the pulse period of Her X-1 with X-ray flux observed by Fermi/GBM are examined. We argue that these regular variations result from free precession of the... 相似文献
16.
Known models proposed to explain the high space velocities of pulsars based on asymmetry of the transport coefficients of different sorts of neutrinos or electromagnetic radiation can be efficient only in the presence of high magnetic fields (to 1016 G) or short rotation periods for the neutron stars (of the order of 1 ms). This current study shows that the observed velocities are not correlated with either the pulsar periods or their surface magnetic fields. The initial rotation periods are estimated in a model for the magnetedipolar deceleration of their spin, aßsuming that the pulsar ages are equal to their kinematic ages. The initial period distribution is bimodal, with peaks at 5 ms and 0.5 s, and similar to the current distribution of periods. It is shown that asymmetry of the pulsar electromagnetic radiation is insufficient to give rise to additional acceleration of pulsars during their evolution after the supernova explosion that gave birth to them. The observations testify to deceleration of the motion, most likely due to the influence of the interstellar medium and interactions with nearby objects. The time scale for the exponential decrease in the magnetic field τD and in the angle between the rotation axis and magnetic moment τß are estimated, yielding τβ = 1.4 million years. The derived dependence of the transverse velocity of a pulsar on the angle between the line of sight and the rotation axis of the neutron star corresponds to the expected dependence for acceleration mechanisms associated with asymmetry of the radiation emitted by the two poles of the star. 相似文献
17.
We apply a population synthesis technique to study the formation and evolution of low-mass X-ray binaries with black holes, observed as X-ray novae, from hierarchical triple systems. A scenario is suggested in which an inner close binary system evolves into an X-ray system with a large mass ratio. The high rate of accretion onto the neutron star leads to a common envelope stage, which may result in the formation of a Thorne-Zytkow (TZ) object. During its evolution, the envelope of the TZ object expands, encompassing the third star. The recurrent common-envelope stage decreases the size of the orbit of the third star, leading to the formation of a lowmass X-ray nova with a black hole. The dynamical stability of triple systems automatically ensures that only lowmass X-ray novae form. We also consider the possible formation of an X-ray nova from a binary in the case of asymmetrical core collapse during a supernova explosion. 相似文献
18.
The question of why the observed periods of anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) cluster in the range 2–12 s is discussed. The possibility that AXPs and SGRs are the descendants of high-mass X-ray binaries that have disintegrated in core-collapse supernova explosions is investigated. The spin periods of neutron stars in high-mass X-ray binaries evolve towards the equilibrium period, which is a few seconds, on average. After the explosion of its massive companion, the neutron star becomes embedded in a dense gaseous envelope, and accretion from this envelope leads to the formation of a residual magnetically levitating disk. It is shown that the expected mass of the disk in this case is 10?7–10?8 M⊙, which is sufficient to support accretion at the rate 1014–1015 g/s over a few thousand years. During this period, the star manifests itself as an isolated X-ray pulsar with a number of parameters similar to those of AXPs and SGRs. The periods of such pulsars can cluster if the lifetime of the residual disk does not exceed the spin-down timescale of the neutron star. 相似文献
19.
I. V. Baikov V. M. Suslin V. M. Chechetkin V. Bychkov L. Stenflo 《Astronomy Reports》2007,51(4):274-281
We propose a new mechanism for type II supernova explosions. An important element of the model is large-scale convection that arises due to non-equilibrium neutronization of the matter in the central region of the proto-neutron star. Our analytical estimates and numerical simulations of the convection rate are in good mutual agreement. Large-scale convection leads to the rapid transport of neutrinos from the center of the star to the bounce shock formed during the pause in the collapse of the stellar matter in the proto-neutron star. The mean neutrino energy is 30–50 MeV. We analyze the dependence of the mean neutrino energy on the size of the convection cells—“bubbles.” Our computations of the interaction between the neutrinos and the shock show that the velocity of the shock along the rotational axis of the star exceeds the escape velocity. Thus, explosion of the envelope and a supernova with a very asymmetrical envelope structure become possible, leading to the formation of a neutron star. 相似文献
20.
Refined analytical expressions for the frequencies corresponding to the Chandler motion of the pole and the diurnal rotation of the deformable Earth are derived. Numerical estimates of the period and amplitude of the polar oscillations are presented. The trajectory of the Chandler polar motion derived via numerical modeling is in qualitative and quantitative agreement with experimental data from the International Earth Rotation Service (IERS). An evolutionary model describing slow variations in the Earth’s rotation parameters under the action of the dissipative moments of the tidal gravitational forces on time scales considerably longer than the precession period of the Earth’s axis is constructed. The axis of the Earth’s figure tends to approach the angular momentum vector of the proper rotation. 相似文献