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1.
The propagation of axially symmetric magnetoelastic waves near the equatorial plane of the crust of a neutron star embedded
in a transverse magnetic field is examined. The crust is treated as a solid-state plasma and waves are excited in it in the
form of a transverse magnetic field applied to the inner boundary of the star’s crust. The time dependent equation is solved
in a linear approximation assuming that the perturbing magnetic field is small compared to the unperturbed field. A simple,
exact solution in the form of linear gaussian beams is obtained without additional conditions being imposed on the dissipation,
dispersion, and narrowness of the beam, provided only that the velocity cn of these waves depends weakly on position. This last condition is satisfied for the plasma in the crust of a neutron star.
As it propagates to the star’s surface, the radius of the beam remains constant. The electric currents generated by the wave
beam on the star’s surface are also calculated.
__________
Translated from Astrofizika, Vol. 50, No. 4, pp. 547–556 (November 2007). 相似文献
2.
The propagation of axisymmetric magnetohydrodynamic waves near the equatorial plane of the crust of a neutron star that is in a transverse magnetic field is considered. These waves are excited by a spatially limited excitation in the form of a transverse magnetic field applied to the inner boundary of the neutron star's crust. The magnetic fields and electric currents excited at the stellar surface by this wave beam are determined. 相似文献
3.
Bahodir B. Ahmedov 《Astrophysics and Space Science》2011,331(2):565-573
The general-relativistic Ohm’s law for a two-component plasma which includes the gravitomagnetic force terms even in the case
of quasi-neutrality has been derived. The equations that describe the electromagnetic processes in a plasma surrounding a
neutron star are obtained by using the general relativistic form of Maxwell equations in a geometry of slow rotating gravitational
object. In addition to the general-relativistic effect first discussed by Khanna and Camenzind (Astron. Astrophys. 307:665,
1996) we predict a mechanism of the generation of azimuthal current under the general relativistic effect of dragging of inertial
frames on radial current in a plasma around neutron star. The azimuthal current being proportional to the angular velocity
ω of the dragging of inertial frames can give valuable contribution on the evolution of the stellar magnetic field if ω exceeds 2.7×1017(n/σ) s−1 (n is the number density of the charged particles, σ is the conductivity of plasma). Thus in general relativity a rotating neutron star, embedded in plasma, can in principle
generate axial-symmetric magnetic fields even in axisymmetry. However, classical Cowling’s antidynamo theorem, according to
which a stationary axial-symmetric magnetic field can not be sustained against ohmic diffusion, has to be hold in the general-relativistic
case for the typical plasma being responsible for the rotating neutron star. 相似文献
4.
The recent discovery of high frequency oscillations during giant flares from the Soft Gamma Repeaters SGR 1806-20 and SGR
1900+14 may be the first direct detection of vibrations in a neutron star crust. If this interpretation is correct it offers
a novel means of testing the neutron star equation of state, crustal breaking strain, and magnetic field configuration. We
review the observational data on the magnetar oscillations, including new timing analysis of the SGR 1806-20 giant flare using
data from the Ramaty High Energy Solar Spectroscopic Imager and the Rossi X-ray Timing Explorer. We discuss the implications for the study of neutron star structure and crust thickness, and outline areas for future investigation.
相似文献
5.
Ya. N. Istomin A. P. Smirnov D. A. Pak 《Monthly notices of the Royal Astronomical Society》2005,356(3):1149-1154
It is shown that the radius of curvature of magnetic field lines in the polar region of a rotating magnetized neutron star can be significantly less than the usual radius of curvature of the dipole magnetic field. The magnetic field in the polar cap is distorted by toroidal electric currents flowing in the neutron star crust. These currents close up the magnetospheric currents driven by the electron–positron plasma generation process in the pulsar magnetosphere. Owing to the decrease in the radius of curvature, electron–positron plasma generation becomes possible even for slowly rotating neutron stars, with PB −2/3 12 < 10 s , where P is the period of star rotation and B 12 = B /1012 G is the magnitude of the magnetic field on the star surface. 相似文献
6.
Using a well-known method for calculating the propagation of waves in an inhomogeneous medium, we have managed to reduce the
problem of wave propagation in pulsar magnetospheres to a system of two ordinary differential equations that allow the polarization
characteristics of the radio emission to be quantitatively described for any magnetic field structure and an arbitrary density
profile of the outflowing plasma. We confirm that for ordinary pulsars (period P ∼ 1 s, magnetic field B
0 ∼ 1012 G, particle production multiplicity parameter λ ∼ 104), the polarization is formed inside the light cylinder at a distance of the order of a thousand neutron star radii. For reasonable
magnetic field strengths and plasma densities on the emission propagation path, the degree of circular polarization is found
to be ∼5–20%, in good agreement with observations. 相似文献
7.
Z. F. Gao N. Wang D. L. Song J. P. Yuan C.-K. Chou 《Astrophysics and Space Science》2011,334(2):281-292
In this paper, an approximate method of calculating the Fermi energy of electrons (E
F
(e)) in a high-intensity magnetic field, based on the analysis of the distribution of a neutron star magnetic field, has been
proposed. In the interior of a neutron star, different forms of intense magnetic field could exist simultaneously and a high
electron Fermi energy could be generated by the release of magnetic field energy. The calculation results show that: E
F
(e) is related to density ρ, the mean electron number per baryon Y
e
and magnetic field strength B. 相似文献
8.
Pulsars are presently believed to be rotating neutron stars with frozen-in magnetic fields. Because of the high density of neutron stars, general relativistic effects are important since they effect both the structure and stability of such stars. Besides this, the magnetic field outside the star is also affected. Instead of falling of asr
(2+l) as in flat space, it is shown that each magnetic multipole varies as a hypergeometric function of radius. A closed form of these hypergeometric functions is given in terms of Legendre functions of the second kind. If the mass of a neutron star exceeds about 2.4m
, the star becomes unstable and coliapses. For a quasistatically collapsing body, it is shown that the magnetic field seen by a distant observer vanishes as the radius approaches the gravitational radius.This work was supported in part by the Air Force Office of Scientific Research, Office of Aerospace Research under AFOSR Grant 70-1866. 相似文献
9.
The propagation of axisymmetric magnetohydrodynamic waves near the equatorial plane of the crust of a neutron star in a transverse magnetic field is considered. The magnetic field is perpendicular to the equatorial plane. The magnetic fields and electric currents excited by this wave beam at the stellar surface are determined. 相似文献
10.
U. Geppert 《Astrophysics and Space Science》1990,168(2):253-261
The influence of magnetic field and rotation on the occurrence of convective instabilities in the liquid layer of neutron star envelopes has been investigated. The critical wavelength
c
, which denotes the boundary between stable and unstable behaviour of convective disturbances, is calculated for a neutron star model as a function of magnetic field and rotation. It is shown that the strength of the magnetic fields of neutron stars strongly suppresses the onset of convection, whereas the limiting effect of rotation acts only if the magnetic field vanishes. 相似文献
11.
Kostas Glampedakis Lars Samuelsson Nils Andersson 《Astrophysics and Space Science》2007,308(1-4):607-611
The presence of a magnetic field in a neutron star interior results in a dynamical coupling between the fluid core and the
elastic crust. We consider a simple toy-model where this coupling is taken into account and compute the system’s mode oscillations.
Our results suggest that the notion of pure torsional crust modes is not useful for the coupled system, instead all modes
excite Alfvén waves in the core. However, we also show that among a rich spectrum of global MHD modes the ones most likely
to be excited by a fractured crust are those for which the crust and the core oscillate in concert. For our simple model,
the frequencies of these modes are similar to the “pure crustal” frequencies. We advocate the significant implications of
these results for the attempted theoretical interpretation of QPOs during magnetar flares in terms of neutron star oscillations.
相似文献
12.
The propagation of nonlinear three-dimensional waves in the form of gaussian beams in pulsars is examined. The defining equations
for the wave motion of a plasma with high particle velocities, high electrical conductivity, high wave frequency, and high
magnetic fields are the standard equations of magnetogas dynamics. Nonlinear, time-dependent equations are derived for relatively
small perturbations of the medium and the orders of magnitude of the parameters of motion such that all the terms in the time-dependent
equation are of the same order are written down. Various directions of the unperturbed magnetic field and of the wave propagation
which may arise during plasma motion in quasars are considered. In a number of cases a closed analytic solution can be constructed
for the propagation of axially symmetric gaussian beams.
__________
Translated from Astrofizika, Vol. 49, No. 3, pp. 409–417 (August 2006). 相似文献
13.
A consistent account of plasma turbulence in magnetohydrodynamics equations describing transport processes across the magnetic field is presented. The structure of the perpendicular shock wave generated in the solar atmosphere, as a result of either local disturbance of the magnetic field or dense plasma cloud motion with a frozen-in magnetic field, has been investigated. The region of parameters in the solar atmosphere at which the electron-ion relative drift velocity u exceeds the electron thermal velocity V
eand generation of radio emission becomes possible, has been determined. The plasma turbulence inside the front has been shown, under conditions of solar corona, not to cause the oscillation structure of shock front to break down. Under chromospheric conditions, the shock profile is aperiodical. Then, the condition u > Vecan be satisfied and shock waves having an Alfvén Mach number M which exceeds the critical value M
c 3.3 for aperiodical shock waves can exist (Eselevich et al., 1971a). Arguments are given in favour of the fact that perpendicular shock waves are generated in the Sun's atmosphere when dense plasma clouds, with a frozen-in magnetic field, are expanded. 相似文献
14.
Natural, low-frequency, hydromagnetic oscillations of an isolated, nonrotating neutron star, which are localized in the peripheral
crust, the structure of which is determined by the electron-nuclear plasma (the Ae phase), are studied. The plasma medium
of the outer crust is treated as a homogeneous, infinitely conducting, incompressible continuum, the motions of which are
determined by the equations of magnetohydrodynamics. In the approximation of a constant magnetic field inside the crust (the
magnetic field outside the star is assumed to have a dipole structure), the spectrum of normal poloidal and toroidal hydromagnetic
oscillations, due to presumed residual fluctuations of flow and their associated fluctuations in magnetic field strength,
is calculated. Numerical estimates given for the periods of MHD oscillations fall in the range of periods of radio pulsar
emission, indicating a close connection between the residual hydromagnetic oscillations and the electromagnetic activity of
neutron stars.
Translated from Astrofizika, Vol. 40, No. 1, pp. 77–86, January–March, 1997. 相似文献
15.
Dipankar Bhattacharya 《Journal of Astrophysics and Astronomy》1995,16(2):217-232
Observational evidence, and theoretical models of the magnetic field evolution of neutron stars is discussed. Observational
data indicates that the magnetic field of a neutron star decays significantly only if it has been a member of a close interacting
binary. Theoretically, the magnetic field evolution has been related to the processing of a neutron star in a binary system
through the spin evolution of the neutron star, and also through the accretion of matter on the neutron star surface. I describe
two specific models, one in which magnetic flux is expelled from the superconducting core during spin-down, via a copuling
between Abrikosov fluxoids and Onsager-Feynman vortices; and another in which the compression and heating of the stellar crust
by the accreted mass drastically reduces the ohmic decay time scale of a magnetic field configuration confined entirely to
the crust. General remarks about the behaviour of the crustal field under ohmic diffusion are also made. 相似文献
16.
Alexander Y. Potekhin Gilles Chabrier Dmitry G. Yakovlev 《Astrophysics and Space Science》2007,308(1-4):353-361
Strong (B?109 G) and superstrong (B?1014 G) magnetic fields profoundly affect many thermodynamic and kinetic characteristics of dense plasmas in neutron star envelopes. In particular, they produce strongly anisotropic thermal conductivity in the neutron star crust and modify the equation of state and radiative opacities in the atmosphere, which are major ingredients of the cooling theory and spectral atmosphere models. As a result, both the radiation spectrum and the thermal luminosity of a neutron star can be affected by the magnetic field. We briefly review these effects and demonstrate the influence of magnetic field strength on the thermal structure of an isolated neutron star, putting emphasis on the differences brought about by the superstrong fields and high temperatures of magnetars. For the latter objects, it is important to take proper account of a combined effect of the magnetic field on thermal conduction and neutrino emission at densities ρ?1010 g?cm?3. We show that the neutrino emission puts a B-dependent upper limit on the effective surface temperature of a cooling neutron star. 相似文献
17.
V. K. Khersonskij 《Astrophysics and Space Science》1984,98(2):255-268
A two-dimensional potential energy surface of an H
2
+
molecular ion is calculated for the case of the strong magnetic field of the neutron starB=1011–1013 G. It is shown that the dependence of the potential energy from the angle between the magnetic field direction and the internuclear axis becomes very sharp as the magnetic field increases. The obtained potential energy surfaces can be used for studying the vibrational-rotational structure of the H
2
+
spectrum in a strong magnetic field and the development of the observational methods for the determination of the magnetic field of a neutron star. 相似文献
18.
Existence of compressive relativistic solitons is established in an arbitrary ξ-direction, inclining at an angle to the direction of the weak magnetic field (ω
pi
≫ω
Bi
) in this plasma compound with ions, relativistic electrons and relativistic electron beams. It is observed that the absolute
linear growth of amplitudes of compressive solitons is due to inactive role of the weak magnetic field and the initial streaming
speeds of relativistic electrons, electron beams, and Q
b
(ion mass to electron beam mass). Besides, the small initial streaming of electrons is found to be responsible to generate
relatively high amplitude compressive solitons. The non-relativistic ions in the background plasma, but in absence of electron-beam
drift and in presence of weak magnetic field are the causing effect of interest for the smooth growth of soliton amplitudes
in this model of plasma. 相似文献
19.
We adopt that in the interior of neutron stars both the proton and neutron superfluids are in the vortex state. Thus, in the superconducting core the magnetic field is expected to be organized in the form of quantized fluxoids. It is shown that fluxoids are buoyant. This gives rise to a rapid (5×104 yr) expulsion of the magnetic field out of the superconducting core to the subcrustal region, and a subsequent decay within the outer crust. The effect considered may be the physical reason why the characteristic decay-time of pulsar magnetic fields (106 yr) corresponds to the ohmic dissipation time within the neutron star crust. The intersection of two types of vortex lines with each other and its possible consequence for pulsars is briefly discussed. 相似文献
20.
本文计算和讨论了强磁场下由冷的催化物质组成的中子星外壳的组份和状态方程。文中考虑了晶格能和强磁场下均匀电子气体的交换能的贡献.得出结论:(1)强磁场使低密度区的状态方程变软;(2)强磁场对高密度区的状态方程几乎没有影响;(3)核质量公式对外壳的组份影响较明显. 相似文献