共查询到20条相似文献，搜索用时 31 毫秒
1.
Thermal conductivity due to Thomson scattering and free-free absorption of photons is numerically evaluated for a non-relativistic non-degenerate plasma in a magnetic field for a number of values ofb =B/kT 1000. In the case of pure scattering, simple fitting formulae are derived. Atb6, the magnetic field is shown to decrease (by about one order) the characteristic densities above which heat transfer is mainly determined by free-free transitions. 相似文献
2.
《Chinese Astronomy and Astrophysics》1983,7(1):61-65
In this paper, I discuss inverse Compton scattering in a strong magnetic field. Using the standard technique in quantum electrodynamics, the solution of Dirac's equation for an electron in a uniform magnetic field and the accurate propagator of electron in a magnetic field, I have calculated the scattering matrix elements in the coordinate representation, the transition probabilities, and found the general formulae for the energy distribution of the scattered photons, and the differential and total scattering cross-sections. 相似文献
3.
R. K. Manchanda 《Journal of Astrophysics and Astronomy》2002,23(3-4):197-212
The attempts at unified model fitting to explain the spectral variations in Cyg X-3 suggest equally probable fits with a combination
of an absorbed blackbody and a separately absorbed power law with an exponential cut-off or a composite of absorbed free-free
emission with a power law hard X-ray component apart from the iron emission line. These seemingly ordinary but ad hoc mixtures
of simple X-ray emission mechanisms have a profound implication about the geometry of the X-ray source. While the first set
suggests a black-hole nature of the compact object, the second combination is consistent with a neutron star binary picture.
The spectral variability at hard X-ray energies above 30 keV can provide crucial input for the unified picture. In this paper,
we present spectral observations of Cyg X-3, made in our on-going survey of galactic and extragalactic X-ray sources in the
20–200 keV energy region, using Large Area Scintillation counter Experiment. The data show a clear power-law photon spectrum
of the form dN/dE ∼ E−2.8 in the 20 to 130 keV energy range. A comparison with earlier data suggests that the total number of X-ray photons in the
entire 2–500 keV energy band is conserved at all time for a given luminosity level irrespective of the state. We propose that
this behaviour can be explained by a simple geometry in which a thermal X-ray source is embedded in a hot plasma formed by
winds from the accretion disk within a cold shell. The high/soft and low/hard X-ray states of the source are simply the manifestation
of the extent of the surrounding scattering medium in which the seed photons are Comptonized and hot plasma can be maintained
by either the X-ray driven winds or the magneto-centrifugal winds. 相似文献
4.
We present computed radiation spectra for the boundary layer (BL) of the accretion disk that is formed near the surface of a neutron star. Both free-free processes and Comptonization were taken into account. Our computations are based on the hydrodynamic solution obtained by Popham and Sunyaev (2001) for the BL structure. The computed spectra are highly diluted compared to the Planck spectra of the same surface temperature. They are complex in shape; in particular, an intense Wien emission component is formed in their high-energy region at high accretion rates. In general, the computed spectra are harder than those observed in actual X-ray sources. This is the result of a very high temperature found by Popham and Sunyaev (2001) for the BL. We show that such temperatures could result from an oversimplified treatment of radiative transfer in their paper, which completely ignored the frequency dependence of the matter opacity and radiation intensity. Our computations indicate that at moderate accretion rates, a proper treatment of radiative transfer with allowance for Comptonization leads to appreciably lower plasma temperatures and to softer radiation spectra. 相似文献
5.
We study the behavior of the solar plasma over the photosphere in the zone of contact of oppositely directed magnetic fields.
A special technique of numerical simulation is used, which allows passing to the class of generalized functions as soon as
the solution loses smoothness. An initial-value problem is solved for the self-consistent nonlinear system of equations of
collisional magneto-gas-dynamics under the assumption that the distribution of physical quantities is two-dimensional and
the plasma has an initial temperature of 50 000 degrees. It is assumed that the magnetic field lines are straight, the physical
quantities are constant along them, and the resulting fluid velocity is perpendicular to the magnetic field. It is shown that
a pinch effect develops under such conditions, which gives rise to much more diverse effects in a natural ambient medium than
in a laboratory plasma. The pinch effect produces narrow, variously directed jets of matter (including those going beyond
the zone of contact of the fields), forms cross-shaped patterns in the distribution of the magnetic field, velocity and density,
and gives rise to specific temperature nonuniformities. In the center of the contact zone, the plasma temperature increases
(we terminate the computations when it doubles). The jet velocity can exceed 20 km/s. 相似文献
6.
A.D.M. Walker 《Planetary and Space Science》1981,29(10):1119-1133
The Kelvin-Helmholtz instability on the magnetopause has frequently been invoked as a mechanism for driving geomagnetic pulsations in the Pc3–Pc5 range, as well as to explain the occurrence of surface waves on the magnetopause observed by satellites. Most theories of the instability represent the magnetopause by a sharp boundary with velocity shear. In this paper a linear theory is developed which takes into account the finite thickness of the low-latitude boundary layer on the magnetopause. The theory is in a form suitable for numerical computation and can take into account the effect of gradients in the plasma pressure, magnetic field magnitude and direction, and density. Computations show that the instability is suppressed at wavelengths short compared with the scale width of the boundary. There is thus a wavelength for which the growth rate is maximum. Extensive computations have been carried out and they show that growth can take place for a very wide range of conditions. The computations confirm earlier results snowing that maximum growth occurs for a wave vector which is perpendicular to the magnetic field. For typical solar wind conditions the theory predicts wavelengths on the magnetopause of the order of 10 times the thickness of the low-latitude boundary layer and periods in the Pc3–Pc5 range. The possible non-linear development of the instability is discussed qualitatively. The predicted results are consistent with satellite observations of pulsations. 相似文献
7.
Z. Medin D. Lai A. Y. Potekhin 《Monthly notices of the Royal Astronomical Society》2008,383(1):161-172
Recent observations of thermally emitting isolated neutron stars revealed spectral features that could be interpreted as radiative transitions of He in a magnetized neutron star atmosphere. We present Hartree–Fock calculations of the polarization-dependent photoionization cross-sections of the He atom in strong magnetic fields ranging from 1012 to 1014 G. Convenient fitting formulae for the cross-sections are given along with the related oscillator strengths for various bound–bound transitions. The effects of finite nucleus mass on the radiative absorption cross-sections are examined using perturbation theory. 相似文献
8.
On the basis of exact computations of the extinction efficiencies of spheroidal absorbing particles, numerical calculations of the extinction curves have been made for a distribution of particle sizes. The results are presented and compared with the observed interstellar extinction. For the sake of comparison, results for the nonabsorbing particles are also given. 相似文献
9.
Y. E. Lyubarsky 《Monthly notices of the Royal Astronomical Society》2002,332(1):199-204
Radiation transfer in a scattering medium in a superstrong magnetic field is considered. Because cross-sections depend on frequency, photons with different energies escape layers with different temperatures and therefore the spectrum of the outgoing radiation differs significantly from the equilibrium blackbody or Bose–Einstein spectrum. It is shown that the emergent spectrum (the photon flux per unit energy band) is flat at low energies. Applications of the result to soft gamma repeaters (SGRs) are discussed. Even though the spectrum is strongly distorted when the radiation propagates through the magnetosphere, a flat segment may be observed in the outgoing spectrum if the surface magnetic field of the neutron star is not too high, B <1015 G . 相似文献
10.
We consider the electron—positron plasma generation processes in the magnetospheres of magnetars—neutron stars with strong surface magnetic fields, B ? 1014–1015 G. We show that the photon splitting in a magnetic field, which is effective at large field strengths, does not lead to the suppression of plasma multiplication, but manifests itself in a high polarization of γ-ray photons. A high magnetic field strength does not give rise to the second generation of particles produced by synchrotron photons. However, the density of the first-generation particles produced by curvature photons in the magnetospheres of magnetars can exceed the density of the same particles in the magnetospheres of ordinary radio pulsars. The plasma generation inefficiency can be attributed only to slow magnetar rotation, which causes the energy range of the produced particles to narrow. We have found a boundary in the \(P - \dot P\) diagram that defines the plasma generation threshold in a magnetar magnetosphere. 相似文献
11.
We show results of numerical simulations of a three component plasma consisting of electrons, ions and dust with external
gravitation and radiation fields. We perform simulation runs, starting from an analytic halo equilibrium, balancing pressure,
gravitational, and radiative forces. Within these the equilibrium is perturbed by the radiation of a typical OB-star association.
The perturbation has a total energy input of 107
L
⊙ and a duration of 30 Myrs. After switching off the perturbation, the simulations are continued to further investigate the
dynamics induced. We start with a self consistent one-fluid MHD model without background magnetic field and show for an asymmetric
case that the system approaches a new equilibrium after switching on the perturbation. Later it relaxes into the starting
configuration again, when the additional radiation is turned off. We then show, first by including a disk-parallel magnetic
field and then by redoing the simulations with a full three-fluid code, the influence of magnetic fields and species separation
on the plasma dynamics. With our computations we demonstrate that these features can be important for the explanation of the
structures of galactic halos and large scale mass flows.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
R. Mewe 《Solar physics》1972,22(2):459-491
The fluxes of about 230 spectral lines in the range 1–60 Å from coronal ions of C, N, O, Ne, Na, Mg, Al, Si, S, Ar, K, Ca, Ti, Cr, Mn, Fe, and Ni are computed for a range of electron temperature from 105 to 109 K. The relative ion abundances are derived from Jordan's ionization equilibrium calculations. The continuum emission is derived from computations of Landini and Monsignori Fossi with a correction for the free-free emission. 相似文献
13.
We describe how a local plasma structure can be changed by a transverse shear flow using numerical simulation to investigate the disturbance process near the magnetopause. The results show that magnetic field lines are bent by transverse shear flow disturbance near the current sheet region. There are multiple bipolar structures of the normal magnetic field in the numerical simulation. We term this new feature as K-point magnetic reconnection, realistic for discussing space observations. 相似文献
14.
A first attempt is made to study the continuous spectrum of linear ideal MHD for 2D solar loops and to understand how 2D effects change the continuum eigenfrequencies and continuum eigenfunctions. The continuous spectrum is computed for 2D solar loops with purely poloidal magnetic fields and it is investigated how non-circularity of the cross-sections of the poloidal magnetic surfaces and variations of density along the poloidal magnetic field lines change the continuous spectrum and induce poloidal wave number coupling in the eigenfunctions. Approximate analytical results and numerical results are obtained for the eigenfrequencies and the eigenfunctions and the poloidal wave number coupling is clearly illustrated. It is found that the continuum frequencies are substantially increased, that the ranges of the continuum frequencies are considerably enlarged and that the derivatives of the continuum frequencies normal to the magnetic surfaces are substantially increased. The eigenfunctions are strongly influenced by poloidal wave number coupling. Implications of these findings for the heating mechanisms of resonant absorption and phase mixing are briefly considered.Research Assistant of the Belgian National Fund for Scientific Research. 相似文献
15.
The Hohlov-Zabolotskaja equation with an additional boundary condition is shown to describe long nonlinear small-amplitude fast sausage surface waves in a magnetic slab embedded in magnetic environment. It is proved that the obtained boundary problem has no solutions in the form of solitary waves. Approximate solution in the form of nonlinear stationary wave is found with the use of expansion in the power series of small amplitude. Second harmonic generation by a sinusoidal wave is studied. The law of energy conservation is obtained. Results of numerical computations are presented. They show that a sinusoidal disturbance does not overturn. The possibility of transmission of wave energy into corona along a magnetic slab is discussed in connection with these results. 相似文献
16.
G. A. Doschek 《Solar physics》1983,86(1-2):49-58
17.
A. Nindos C. E. Alissandrakis G. B. Gelfreikh M. R. Kundu K. P. Dere A. N. Korzhavin V. M. Bogod 《Solar physics》1996,166(1):55-87
We present multi-frequency observations and model computations of the microwave emission of a solar active region. The radio observations were obtained with the RATAN-600 at several wavelengths between 0.8 and 31.6 cm and with the VLA at 6 and 20 cm. The active region was also observed in the EUV O Iv lines by the HRTS instrument aboard the Space Shuttle Spacelab-2 mission. These lines are formed in the chromosphere-corona transition region and their intensity ratio is sensitive to pressure. Photospheric magnetograms provided both the longitudinal and the transverse component of the magnetic field. The microwave observations were checked against model computations taking into account both the free-free and the gyro-resonance emission mechanisms and using the pressure data from the O IV lines. The magnetic field was computed through constant- force-free extrapolations of the longitudinal photospheric field. We computed both the flux from 2 to 20 cm and the spatial structure of the microwave emission at 6 and 20 cm. The comparison of the computed and observed flux spectra allowed us to estimate the magnetic field strength at the base of the transition region and in the low corona, as well as the values of the conductive flux and the height of the base of the transition region. The model maps at 6 cm and 20 cm showed that was not constant above the active region; the same conclusion was reached on the basis of the photospheric observations. The use of pressure measurements allowed us to identify microwave structures which were determined by pressure enhancements. At 6 cm the computations confirmed the fact that the magnetic field is the principal factor that determines the structure of sunspot-associated sources and showed that the effect of pressure variations was small. Pressure variations were more important at 20 cm, where the peak of the emission was associated with the sunspot and a diffuse component was associated with the plage which had an average pressure higher by a factor of 1.54 than the sunspot. 相似文献
18.
F. W. Stecker 《Astrophysics and Space Science》1973,20(1):47-57
The production of ultrahigh energy photons, electrons and neutrinos as the decay products of pions produced in photomeson interactions between cosmic-ray nucleons and the blackbody microwave background is discussed in terms of the resultant energy spectra of these particles. Simple asymptotic formulas are given for calculating the ultrahigh energy photon spectrum predicted for the universal cosmic-ray hypothesis and the resulting spectra are compared with those obtained previously by numerical means using a different propagation equation for the photons. Approximate analytic solutions for the photon spectra are given in terms of simple power-law energy functions and slowly varying logarithmic functions. These can be used to estimate ultrahigh energy photon fluxes for various astrophysical parameters. The generic relation between the various secondary components is then discussed in terms of their astrophysical implications which are summarized in the conclusion. 相似文献
19.
本文在考虑磁光效应条件下,根据对斯托克斯参数转移方程组求得的数值解,计算了单极太阳黑子的线偏振讯号的单色像,并与美国马歇尔空间飞行中心的观测资料进行了对比,结果表明,径向黑子磁场模型给出与观测相似的单色像,而旋涡形模型导致与观测有显著差异的图像。因此可以认为径向模型更接近于实际情况。 相似文献
20.
Gianfranco De Zotti 《Astrophysics and Space Science》1975,33(2):359-367
A non-relativistic calculation of the free-free opacity is made in detail for the conditions of intermediate and strong electron degeneracy. Corrections to the Born approximation are included and the ion correlations as well as the electron screening of the nuclear charge are taken into account. The free-free opacity is compared with the conductive one. It is shown that it must be taken into account when the degeneracy is not too strong, that is in the temperature-density regime where the plasma frequency ω p satisfies the condition ω p ? 2.5kT. 相似文献