A weak outburst of the millisecond X-ray pulsar SAX J1808.4-3658 in October 1996 as detected from RXTE slew data     

M. G. Revnivtsev 《Astronomy Letters》2003,29(6):383-386

Analysis of the RXTE slew data in October 1996 revealed a weak X-ray burst from the millisecond pulsar SAX J 1808.4-3658. The 3–20-keV energy spectrum of the source can be described by a power law with an index of 2.0 and a(3-to 20 keV) luminosity of ～1.4×10³⁵ erg s^?1 (the distance to the source was taken to be 2.5 kpc). Because of the short exposure time, we failed to detect weak pulsations at a frequency of 401 Hz in the source. The (2σ) upper limit of the pulse fraction is ～13%.  相似文献   

CO-Observations of post-starburst galaxies     

Marco Barden  Linda J. Tacconi  Matthew D. Lehnert  Dimitra Rigopoulou 《Astrophysics and Space Science》2001,277(1):95-95

  相似文献   

Evolution of short period meteoroid streams     

P. B. Babadzhanov  Yu. V. Obrubov 《Celestial Mechanics and Dynamical Astronomy》1992,54(1-3):111-127

The dynamical evolution of meteoroid streams associated with cornets Encke, Halley, Machholz 1986 VIII and asteroid Phaethon is discussed. It is shown that the planetary perturbations can greatly increase the streams thickness and each stream may produce several couples of meteor showers active in different seasons of the year. The theoretical and observed data are in a satisfactory accordance.  相似文献   

Dissipative-acoustic instability in accretion disks at a nonlinear stage     

A. V. Khoperskov  S. S. Khrapov  E. A. Nedugova 《Astronomy Letters》2003,29(4):246-257

Nonstationary hydrodynamic models of a viscous accretion disk around a central compact object were constructed. Two different numerical methods (TVD and SPH) are used to study the dynamics of dissipatively unstable acoustic perturbations at the nonlinear stage in terms of the standard α-disk model. The standard disk accretion in the Shakura-Sunyaev model is unstable against acoustic waves for various parameters of the system. If the α parameter, which specifies the level of turbulent viscosity, exceeds α?0.03, then a complex nonstationary system of small-scale weak shock waves is formed. The growth rate of the perturbations is higher in the central disk region. For α?0.2, the relative shock amplitude can exceed 50% of the equilibrium disk parameters. The reflection of waves from the disk boundaries and their nonlinear interaction are important factors that can produce unsteady accretion. The luminosity of such a disk undergoes quasi-periodic oscillations at a level of several percent (?5%) of the equilibrium level.  相似文献   

Exchange and correlation interactions in electron-positron plasma     

A. V. Yudin  D. K. Nadyozhin 《Astronomy Letters》2003,29(3):158-162

The effect of particle-particle interaction on the adiabatic index γ for an electron-positron plasma is considered. An improved method for numerically calculating the Hartree-Fock exchange integral is presented and its relativistic asymptotics is determined. An approximation formula is derived for the correlation part of the interaction in the low-density limit. This formula includes degeneracy and the positron component.  相似文献   

Some integrable cases of the two-body problem with mass depending both on time and distance     

J. A. Docobo 《Astronomy Letters》2003,29(5):344-347

an extension of the Gylden-Meshcherskii problem when the mass depends both on time and distance between two bodies is considered. certain mass loss laws as well as the Meshcherskii position vector and time transformation are used to convert the problem into the cases with equations of motion arising from integrable potentials.  相似文献   

Spine–sheath polarization structures in four active galactic nuclei jets     

A. B. Pushkarev  D. C. Gabuzda  Yu. N. Vetukhnovskaya  V. E. Yakimov 《Monthly notices of the Royal Astronomical Society》2005,356(3):859-871

We present the results of multifrequency (15 + 8 + 5 GHz) polarization Very Long Baseline Array (VLBA) observations of the three BL Lacertae objects 0745+241, 1418+546 and 1652+398 together with 5-GHz VLBI Space Observatory Programme (VSOP) observations of 1418+546 and 1.6- and 5-GHz VSOP observations of the blazar 1055+018. The jets of all these sources have polarization structure transverse to the jet axis, with the polarization E vectors aligned with the jet along the jet spine and 'sheaths' of orthogonal E vectors at one or both edges of the jet. The presence of polarization aligned with the jet near the 'spine' may indicate that the jets are associated with helical B fields that propogate outward with the jet flow; the presence of orthogonal polarization near the edges of the jet may likewise be a consequence of a helical jet B field, or may be owing to an interaction with the ambient medium on parsec scales. We have tentatively detected interknot polarization in 1055+018 with E aligned with the local jet direction, consistent with the possibility that the jet of this source is associated with a helical B field.  相似文献   

Faint galaxies: merging model of E/SO galaxies     

Wen Xu  Yunqiang Yu 《Astrophysics and Space Science》1995,226(2):309-328

We study a model of mergers affecting only the progenitors of present E/SO. We adopt the standard scenarios of star formation as prescribed by Guiderdoni & Rocca-Volmerange. The merging process is parametrized under the assumptions of(1) self-similarity of the Schechter MF and(2) mass conservation. Nine models are discussed. The predictions are compared with counts ofB _J ,U ⁺,F ⁺,N ⁺ bands. E/SO mergers account for the excess of the faintest blue galaxies without causing excess in redder bands. However, as we no longer have enough mergers at brighter magnitudes, a plain E/SO merging model fits less tightly for the redshift and the colour distributions. Detection effect, a steeper slope of LF may be ways to improve. Our models predict acceptable merger frequencies atz = 0.5 although some models predict more interacting galaxies than observation atz = 0.  相似文献   

A kinetic model of gas flow in a porous cometary mantle     

Yu. V. Skorov  H. Rickman   《Planetary and Space Science》1995,43(12)

A numerical study of gas flow through a porous cometary mantle is presented. A kinetic model based on the well-known Test Particle Monte Carlo Method for the solution of rarefied gas dynamics problems is proposed. The physical model consists of two spatial plane regions: the condensed ice phase and a porous dust mantle. The structure of the porous dust layer is described as a bundle of cylindrical inclined channels not crossing each other. A vertical temperature gradient may exist across the dust mantle. The aim is to investigate how the characteristics of molecular flow depend on the capillary length, inclination angle, and temperature gradient. Examples illustrating a significant deviation of some results from equilibrium values are shown. In particular, the gas velocity distribution at both ends of the pore is strongly non-Maxwellian if there is an important temperature contrast across the pore. The emergent gas flow rate is found to vary with the pore length/radius ratio in excellent agreement with Clausing's empirical formula. The degree of collimation of the flow is quantitatively studied as a function of the length/radius ratio, and consequences for the jet force of outgassing through a dust mantle or, indeed, a rough surface are estimated.  相似文献   

Computer simulation of the particle acceleration in pulsar magnetospheres     

Yu. A. Rylov 《Astrophysics and Space Science》1987,132(2):353-386

In the spherically-symmetric case, a computer simulation of the electron acceleration inside the outflow channel of the pulsar magnetosphere is produced. The stationary motion of electrons is shown to be unstable in the case of > _c, where is a parameter describing inhomogeneity of the background charge, and _c is its critical value. The arising non-stationary motion of electrons leads to a formation of electron bunches, which move chaotically. The mean electron energy appears to be much greater at the non-stationary motion, than at the stationary one. The time-averaged parameters of the non-stationary electron flow and their dependence upon have been investigated. Distributions of the mean values of parameters (charge density, electron velocity, electric field energy density, pressure, and internal energy of the gas composed of the electron bunches) over the magnetosphere altitude have been investigated. The mean spectra of the charge density have been obtained. The results of numerical investigation of the spherically-symmetric model are used for estimation of the electron energy and of the electron flux in the case of the more realistic model. The radioemission loss is estimated, and is shown to be large enough for explaining the radiopulsar phenomenon as a thermal radioemission of the pulsar magnetosphere. In particular, such common properties of the pulsar radioemission as the high bright temperature, the sharp radioemission directivity, and the characteristic turn-over of the radioemission spectrum at the frequency of the order 10⁸ Hz are found a natural explanation in frames of this model.  相似文献