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1.
Ambient electron heating rates along several magnetic field lines have been determined for subsequent studies of electron and ion temperatures. Use is made of the modified diffusion method for computing the heating of the ambient plasma, and the escape fluxes from both hemispheres are coupled by self-consistent upper boundary conditions supplied by interhemispheric fluxes degraded in energy along the magnetic field tubes. Heating rates and fluxes are presented for several low L-shells appropriate for noon solstice conditions when both hemispheres are illuminated. The opacity of the field tubes as a function of L is expected to go through a minimum due to the transition from large collective effects of coulomb small angle scattering and energy loss for high L-shells, to a domination by neutral scattering all along the field lines of low L-shells.  相似文献   

2.
The effect of a strong magnetic field on neutron stars or white dwarfs is calculated for Thomson scattering in a strong magnetic field with radiation damping. The Stokes's parameters for the scattered radiation are computed explicitly in terms of the state of polarization of the incident wave, the electrocyclotron frequency, the angle of incidence, and the angle of scattering. The criterion for the magnetic field to substantially affect the Stokes's parameters is that the photon frequency be less than the electrocyclotron frequency. The effects of classical radiation damping are explicitly taken into account by using the Abraham-Lorentz equation. The corresponding quantum mechanical treatment for Compton scattering in a relativistic electron gas is now under investigation.  相似文献   

3.
The dependence of geomagnetic activity during a recurrent magnetic storm on the solar-wind magnetic field and plasma parameters has been studied. According to variations of solar-wind magnetic field strength B, a recurrent magnetic storm is divided into two stages: the first proceeding during the peak of B, and the second proceeding after the return of B to quiet level. The Kp index vs solar-wind parameters scattering diagrams for stages I and II differ significantly. In particular, the random scattering for stage I is much larger than for stage II. It was found that for stage I the Kp index correlates with B, with the sign and value of northsouth field component Bz and with the magnitude ΔB of field fluctuations, the situation being similar to that during sporadic magnetic storms, though the scale of the event is smaller. For stage II, the Kp index does not correlate with B, but strongly correlates with ΔB and weaker—with Bz. So geomagnetic activity at stage II is supported mainly by solar-wind magnetic field fluctuations. The dependence of the Kp index on plasma parameters (concentration of protons n, bulk velocity v and temperature T) is weak for both stages.  相似文献   

4.
The problem of the effect of a strongly magnetic star on a surrounding accretion disc is considered. For stellar rotation periods greater than a critical value, a numerical solution is found for a steady disc with turbulent magnetic diffusion, including electron scattering opacity and radiation pressure. Inside the corotation radius, the extraction of disc angular momentum by magnetic coupling to the star becomes strong and this leads to enhanced viscous stress and dissipation. The resulting elevated temperature causes electron scattering opacity and radiation pressure to become significant further from the star than in the absence of its magnetic field. The disc ends as its height increases rapidly due to the large central pressure, its density decreases and magnetically induced viscous instability occurs.  相似文献   

5.
Heat transfer through weakly magnetized diffuse astrophysical plasmas excites whistlers. This leads to electron whistler resonant scattering, a reduction of the electron mean free path, and heat flux inhibition. However, only whistlers propagating at a finite angle to the magnetic field (off-axis) can scatter the heat flux carrying electrons. Thus the level of heat flux inhibition along the magnetic field lines depends on the presence of off-axis whistlers.   We obtain a solution of the Boltzmann equation with the whistler wave equation and show that if εthβe ≫ 10−4, where εth is the thermal collisional Knudsen number and βe is the ratio of the electron pressure to the magnetic energy density, then scattering of heat flux carrying electrons by off-axis whistlers, which are shown to propagate at about 65δ, is efficient enough to lead to heat flux inhibition along field lines. The inhibition so obtained is proportional to (εthβe)−1.  相似文献   

6.
The expressions are derived for thermal and electric conductivities as well as thermopower of a degenerate relativistic electron gas in the surface layers of neutron stars along the magnetic fieldB=4×1011–1014G for two scattering mechanisms of electrons, namely, for Coulomb scattering on ions in the ion-liquid regime and on high-temperature phonons in the solid regime. The results may be of use to study neutron star cooling rates, nuclear burning of the matter in the surface layers, diffusion of the magnetic field, etc.  相似文献   

7.
The Milne problem is solved numerically for a magnetized semi-infinite electron atmosphere in the case where the magnetic field is directed along the normal to the medium. The calculated angular distribution, degree of linear polarization, and positional angle of inclination of the plane of polarization of the emerging radiation are given in tables for a number of values of the Faraday rotation parameter and for degrees of intrinsic optical absorption, q=0, 0.2, and 0.4. It is assumed that the magnetic field B106 G, so that scattering in the optical range is purely Thomson scattering.  相似文献   

8.
Compton scattering of electromagnetic radiation in pulsar magnetospheres   总被引：2，自引：0，他引：2  
We have considered the spontaneous Compton scattering of radiation in the magnetic field by both a single ultra-relativistic electron and a system of electrons with the power-law energy distribution. The degree of radiation anisotropy was assumed arbitrary. Parameters of the scattering-generated radiation for the entire range of post-scattering photon energies are given in the paper for all possible scattering modes.  相似文献   

9.
It is proposed that the region containing fast particles, electrostatic and electromagnetic fields, around active galactic nuclei is responsible for generating electromagnetic emissions from -rays to radio waves. The electrons are accelerated by Langmuir turbulence originating through the process of Raman forward scattering (RFS). The radiation mechanism is stimulated Raman backward scattering (RBS) where the fast electron beam loses energy by scattering over spatially periodic magnetic field. The spatially periodic magnetic field results from the magnetic modulational instability of the Langmuir waves. This model accounts well for the large luminosities observed in active galactic nuclei over -rays to radio waves and in addition it relates physically the emission regions at different wavelengths.  相似文献   

10.
The on-going Parkes multibeam survey has been astoundingly successful (Manchesteret al. 2001), and its discovery of over 600 pulsars has opened up new avenues for probing the Galaxy’s electron content and magnetic field. Here we report on recent observations made with the Arecibo 305-m telescope, where 80 distant, high dispersion measure pulsars (of which 35 are from the multibeam survey) were studied at multiple frequency bands in the range 0.4–2.4 GHz, in order to determine their scattering properties, rotation measures and spectral indices. The results will be used to meet a variety of science goals; viz., creating an improved model of the electron density, mapping out the Galactic magnetic field, and modeling the pulsar population.  相似文献   

11.
The technique of electron reflectometry, a method for remote estimation of planetary magnetic fields, is expanded from its original use of mapping crustal magnetic fields at the Moon to achieving the same purpose at Mars, where the presence of a substantial atmosphere complicates matters considerably. The motion of solar wind electrons, incident on the martian atmosphere, is considered in detail, taking account of the following effects: the electrons' helical paths around the magnetic field lines to which they are bound, the magnetic mirror force they experience due to converging field lines in the vicinity of crustal magnetic anomalies, their acceleration/deceleration by electrostatic potentials, their interactions with thermal plasma, their drifts due to magnetic field line curvature and perpendicular electric fields and their scattering off, and loss of energy through a number of different processes to, atmospheric neutrals. A theoretical framework is thus developed for modeling electron pitch angle distributions expected when a spacecraft is on a magnetic field line which is connected to both the martian crust and the interplanetary magnetic field. This framework, along with measured pitch angle distributions from the Mars Global Surveyor (MGS) Magnetometer/Electron Reflectometer (MAG/ER) experiment, can be used to remotely measure crustal magnetic field magnitudes and atmospheric neutral densities at ∼180 km above the martian datum, as well as estimate average parallel electric fields between 200 and 400 km altitude. Detailed analysis and full results, concerning the crustal magnetic field and upper thermospheric density of Mars, are left to two companion papers.  相似文献   

12.
A general scheme is established to examine any magnetohydrodynamic (MHD) configuration for its acceleration potential including the effects of various types of plasma waves. The analysis is restricted to plasma waves in a magnetic field with electron cyclotron frequency less than, but comparable to, the electron plasma frequency (moderate field). The general role of electron plasma waves is examined in this paper independent of a specific MHD configuration or generating mechanism in the weak turbulence limit. The evolution of arbitrary wave spectra in a non-relativistic plasma is examined, and it is shown that the nonlinear, process of induced scattering on the polarization clouds of ions leads to the collapse of the waves to an almost one-dimensional spectrum directed along the magnetic field. The subsequent acceleration of non-relativistic and relativistic particles is considered. It is shown for non-relativistic particles that when the wave distribution has a negative slope the acceleration is retarded for lower velocities and enhanced for higher velocities compared to acceleration by an isotropic distribution of electron plasma waves in a magnetic field. This change in behavior is expected to affect the development of wave spectra and the subsequent acceleration spectrum.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

13.
A midly relativistic quantum-mechanical treatment of the Compton scattering cross-section in a strong magnetic field regime appropriate to observed electron temperature and field strengths in a neutron star magnetosphere is provided. The approximations used in the evaluation of the electron propagator are different from those employed previously and lead finally to simpler and more usable expressions for the cross-section.Various conceptual difficulties with the quantum cyclotron line mechanism are also discussed and the problem of the translational invariance of the Hamiltonian commonly used is addressed.  相似文献   

14.
We consider the transfer of radiation and calculate the force of its pressure in the electron gyroresonance line in the atmospheres of magnetic degenerate stars. We specify the atmospheric parameters for which an outflow of plasma is possible under radiation pressure in the cyclotron line. We show that the permittivity tensor of a mildly relativistic plasma in a strong magnetic field found by applying relativistic corrections to the cyclotron resonance condition and by taking into account the vacuum polarization and recoil effects during photon scattering should be used to obtain proper results. We have determined the real and imaginary parts of the refractive indices and the polarization coefficients for normal electromagnetic waves when scattering dominates over absorption. Relativistic effects, which change greatly the dispersion and resonant absorption of waves propagating almost perpendicular to the magnetic field, and vacuum polarization have been found to change qualitatively the gyroresonance radiation spectrum and pressure for a wide range of parameters of stellar magnetospheres.  相似文献   

15.
本文认为强磁场中的逆Compton散射可能是γ射线爆的主要辐射机制.其能谱是由源区质子产生的低频光子经强磁场中非热电子的Compton散射形成的.我们利用非相对论情形(B/B_(cr)≤1,hv_i/m_ec~2≤1)下强磁场中的Compton散射微分截面,导出了上述Compton散射的辐射谱公式,由此很好地拟合了典型γ射线爆GB811016的观测能谱.  相似文献   

16.
Studies of Compton scattering by relativistic electrons in a strong magnetic field have been restricted to either incident photon angles θ′ aligned along the magnetic field B or incident photon energies ω′ below the first pair creation threshold $\omega'_{PC}$ . When these restrictions are relaxed there is a resonance in Compton scattering associated with pair creation (PC), that is analogous to but independent of known resonances associated with gyromagnetic absorption (GA). As with the GA resonances, that may be labeled by the Landau quantum numbers of the relevant states, there is a sequence of PC resonances where the scattering cross section diverges. In this paper, the lowest divergence is studied for incident photon energies satisfying ω′2sin2 θ′/(2eB)?1, assuming that the scattering electron is in its ground (Landau) state. This lowest resonance affects only parallel-polarized photons.  相似文献   

17.
The radial structure of a thin accretion disc is calculated in the presence of a central dipole magnetic field aligned with the rotation axis. The problem is treated using a modified expression for the turbulent magnetic diffusion, which allows the angular momentum equation to be integrated analytically. The governing algebraic equations are solved iteratively between 1 and 104 stellar radii. An analytic approximation is provided that is valid near the disruption radius at about 100 stellar radii. At that point, which is approximately 60 per cent of the Alfvén radius and typically about 30 per cent of the corotation radius, the disc becomes viscously unstable. This instability results from the fact that both radiation pressure and opacity caused by electron scattering become important. This in turn is a consequence of the magnetic field which leads to an enhanced temperature in the inner parts. This is because the magnetic field gives rise to a strongly enhanced vertically integrated viscosity, so that the viscous torque can balance the magnetic torque.  相似文献   

18.
H. Frisch 《Solar physics》1996,164(1-2):49-66
Resonance polarization, which is created by the scattering of an anisotropic radiation field in regions of zero or weak magnetic fields, is strongly dependent on the frequency redistribution taking place during the scatterings. Here we discuss the frequency redistribution matrix relevant to resonance lines, concentrating on linear polarization. First we analyze in detail the redistribution matrix in a zero magnetic field given by the theory of Omont, Smith and Cooper (1972), revisited by Domke and Hubeny (1988). We explain that the linear polarization maxima which may appear in the wings of the Stokes Q profiles of strong resonances lines such as the Ca I 4227 Å line are coherent frequency redistribution effects. Various approximate forms of the frequency redistribution matrix are also examined. For resonance polarization in a weak magnetic field, we suggest a new expression for the redistribution matrix which can be used at all line frequencies, and is consistent with the condition that the Hanle effect acts only in the line core.  相似文献   

19.
It has been postulated that electron bremsstrahlung in a strong external magnetic field is the dominant radiation mechanism within the accretion plasma near the magnetic polar regions of binary X-ray sources. Earlier works on the cross section for such a process proved to be unsatisfactory.The present work uses the simple structure of the propagator obtained in a previous calculation for mildly relativistic electrons occupying no more than the first few Landau levels. Particular emphasis is put on the integration over the possible range of momentum transfer during a single collision with the ion. Typical behaviour for two linear polarization modes is illustrated for forward and backward electron scattering. It is found that the previously predicted behaviour at low frequencies for the two modes is only correct in the limit of weak field and large momentum transfer. At higher frequencies resonances are present irrespective of the polarization of the emitted radiation.  相似文献   

20.
Equipartition magnetic fields can dramatically affect the polarization of radiation emerging from accretion disc atmospheres in active galactic nuclei. We extend our previous work on this subject by exploring the interaction between Faraday rotation and absorption opacity in local, plane-parallel atmospheres with parameters appropriate for accretion discs. Faraday rotation in pure scattering atmospheres acts to depolarize the radiation field by rotating the polarization planes of photons after last scattering. Absorption opacity in an unmagnetized atmosphere can increase or decrease the polarization compared to the pure scattering case, depending on the thermal source function gradient. Combining both Faraday rotation and absorption opacity, we find the following results. If absorption opacity is much larger than scattering opacity throughout the atmosphere, then Faraday rotation generally has only a small effect on the emerging polarization because of the small electron column density along a photon mean free path. However, if the absorption opacity is not too large and it acts alone to increase the polarization, then the effects of Faraday rotation can be enhanced over those in a pure scattering atmosphere. Finally, while Faraday rotation often depolarizes the radiation field, it can in some cases increase the polarization when the thermal source function does not rise too steeply with optical depth. We confirm the correctness of the analytic calculation by Silant'ev of the high magnetic field limit of the pure scattering atmosphere, which we incorrectly disputed in our previous paper.  相似文献   

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