共查询到20条相似文献，搜索用时 484 毫秒
1.
本文讨论的是中子星自洽的有限磁层大气模型,先用试探解方法得到一个解析解,它给出有限磁层大气的分布轮廓,然后用能量最小原理讨论了其特性,取得了有意义的结果。同时,通过对其等离子体与真空交界面的研究,得出其交界面也是稳定的。最后,我们对模型的发展作了展望,指出赤道区的超共转,可能与子脉冲漂移有关,从这个模型出发,我们将可能最终建立一个自洽的有辐射的模型。 相似文献
2.
V. S. Morozova B. J. Ahmedov A. A. Abdujabbarov A. I. Mamadjanov 《Astrophysics and Space Science》2010,330(2):257-266
Plasma magnetosphere surrounding rotating magnetized neutron star in the braneworld has been studied. For the simplicity of calculations Goldreich-Julian charge density is analyzed for the aligned neutron star with zero inclination between magnetic field and rotation axis. From the system of Maxwell equations in spacetime of slowly rotating star in braneworld, second-order differential equation for electrostatic potential is derived. Analytical solution of this equation indicates the general relativistic modification of an accelerating electric field and charge density along the open field lines by brane tension. The implication of this effect to the magnetospheric energy loss problem is underlined. It was found that for initially zero potential and field on the surface of a neutron star, the amplitude of the plasma mode created by Goldreich-Julian charge density will increase in the presence of the negative brane charge. Finally we derive the equations of motion of test particles in magnetosphere of slowly rotating star in the braneworld. Then we analyze particle motion in the polar cap and show that brane tension can significantly change conditions for particle acceleration in the polar cap region of the neutron star. 相似文献
3.
Observed hot spots on neutron stars are often associated with polar caps heated by the backflow of energetic electrons or positrons from accelerators on bundles of open magnetic field lines. Three effects are discussed that may be relevant to formation of hot spots and their areas. (1) The area of a polar cap is proportional to the ratio of the star’s surface dipole field to the local field at the polar cap. Because the field is coupled to the evolving spin of the superfluid core of the star, this ratio can depend on the stellar spin and its history. (2) The hot emission area may appear smaller to a distant observer when emitted X-rays propagate through electron-positron plasma created in the magnetosphere. The X-rays then change their energy spectrum because of cyclotron resonant scattering by pairs. (3) Hot spots may form on the star’s surface as a result of crust motions that are driven by the pull of core flux tubes pinned to the crust. Such motions twist the footprints of closed magnetic loops of the magnetosphere and induce an electric current in the loop, which will heat those footprints. 相似文献
4.
Yu. A. Rylov 《Astrophysics and Space Science》1981,75(2):423-436
The case of an aligned rotator magnetosphere is considered. Provided the ions ejection from the neutron stellar surface is absent, the pulsar magnetosphere consists of two polar electron caps. The upper parts of the caps are unstable. Electrons precipitate from these parts, fall onto the star and are accelerated to Lorentz-factor 106–107. Electrons radiate -quanta in the direction of the star. These -quanta are converted into electron-positron pairs. The region of size, about 10 stellar radii, around the star appears to be filled with electron-positron plasma. The inflow of electron-positron plasma interacts with the electron gas of the polar cap. For this reason longitudinal plasma vibrations arise, and bunched outflows of electron-positron plasma appear. 相似文献
5.
I. A. Smith F. C. Michel P. D. Thacker 《Monthly notices of the Royal Astronomical Society》2001,322(2):209-217
We present detailed numerical simulations of the magnetosphere of an isolated neutron star in which the spin and magnetic dipole axes of the star are aligned. We demonstrate that stable charge distributions are always found, rather than particle outflows. A stable magnetosphere consists of a dome above the polar cap containing plasma of one charge and an equatorial belt containing plasma of the other sign: E · B =0 inside both of these. These are separated by a vacuum gap in which E · B ≠0 ( ρ =0 instead). We show that the charge distribution used in the 'standard' Goldreich–Julian pulsar model is inherently unstable: it collapses to a stable configuration that is very similar to the others illustrated here. An instructive video of this collapse is available at http://spacsun.rice.edu/~ian/. For typical pulsars, the stable solution has no particles near to the light cylinder, and if there were any there then their loss from the system would not lead to a replacement from the star (in contradiction to the explicit assumption used in the Goldreich–Julian model). We discuss the generic effects of pair creation, in particular as an additional source of ionization in the vacuum gap. The overall effect is simply to reduce the value of E · B in the vacuum gap so that the pair-production rate drops towards zero. A dome, disc and gap geometry is still the resulting solution. In conclusion, we confirm previous studies that the aligned rotator cannot make an active pulsar. 相似文献
6.
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
7.
The model of a magnetized rotating neutron star with an electric current in the region of its fluid polar magnetic caps is considered. The presence of an electric current leads to differential rotation of the magnetic caps. The rotation structure is determined by the electric current density distribution over the surface. In the simplest axisymmetric configuration, the current flows in one direction near the polar cap center and in the opposite direction in the outer ring (the total current is zero for the neutron star charge conservation). In this case, two rings with opposite directions of rotation appear on the neutron star surface, with the inner ring always lagging behind the star’s main rotation. The differential rotation velocity is directly proportional to the electric current density gradient along the polar cap radius. At a width of the region of change in the electric current from 1 to 102 cm and a period ～1 s and a magnetic field B ～ 1012 G typical of radio pulsars, the linear differential rotation velocity is ～10?2–10?4 cm s?1 (corresponding to a revolution time of ～0.1–10 yr). 相似文献
8.
F. C. Michel 《Astrophysics and Space Science》1980,72(1):175-181
We conclude that the magnetospheric structure around an aligned rotating magnetized neutron star, in the case of a completely charge-separated plasma, consists of a dome of charge about the polar caps and an equatorial disk of opposite charge which, together, entirely envelope the surface but do not fill the magnetosphere. Although the aligned rotator is a standard model for analyzing pulsar emission, the magnetosphere we obtain need not emit particles and need not generate a stellar wind, contrary to previous expectations. Pair production only seems to modify the detailed shape of the dome and disk, such modification serving to shut off further pair production. Such a magnetohydrodynamically inactive object may have difficulty simulating pulsar emission.Research support in part by the National Science Foundation under grant AST 77-22675. 相似文献
9.
Ernazar B. Abdikamalov Bobomurat J. Ahmedov John C. Miller 《Monthly notices of the Royal Astronomical Society》2009,395(1):443-461
Just as a rotating magnetized neutron star has material pulled away from its surface to populate a magnetosphere, a similar process can occur as a result of neutron-star pulsations rather than rotation. This is of interest in connection with the overall study of neutron star oscillation modes but with a particular focus on the situation for magnetars. Following a previous Newtonian analysis of the production of a force-free magnetosphere in this way Timokhin et al., we present here a corresponding general-relativistic analysis. We give a derivation of the general relativistic Maxwell equations for small-amplitude arbitrary oscillations of a non-rotating neutron star with a generic magnetic field and show that these can be solved analytically under the assumption of low current density in the magnetosphere. We apply our formalism to toroidal oscillations of a neutron star with a dipole magnetic field and find that the low current density approximation is valid for at least half of the oscillation modes, similarly to the Newtonian case. Using an improved formula for the determination of the last closed field line, we calculate the energy losses resulting from toroidal stellar oscillations for all of the modes for which the size of the polar cap is small. We find that general relativistic effects lead to shrinking of the size of the polar cap and an increase in the energy density of the outflowing plasma. These effects act in opposite directions but the net result is that the energy loss from the neutron star is significantly smaller than suggested by the Newtonian treatment. 相似文献
10.
We consider a system consisting of a neutron star surrounded by a disc of dense degenerate matter, and study the sequence of events following the impact of comets on to the disc. The direct signature of the impact event is a short burst of high-energy radiation (X-rays to UV, depending on the impact location) emitted from the bubble of hot gas created at the impact site. We assume that the bubble is confined by the magnetic field of the central neutron star. Part of the bubble matter may be channelled along magnetic field lines and rain down on the polar caps. The surface density at the neutron star surface may be sufficient to initiate a runaway thermonuclear reaction. These X-rays or the direct effect of the transferred plasma crossing charge-depleted regions in the outer magnetosphere may re-ignite an otherwise dead pulsar. 相似文献
11.
Yu. A. Rylov 《Astrophysics and Space Science》1977,51(1):59-75
Numerical calculations of the electron cap shape of a rapidly rotating neutron star with a strong magnetic field have been provided. It is supposed that the magnetic dipole axis is aligned, and ejection of positive charged particles from the star's surface absent. The total charge of the star has been calculated. Estimation of the character of charged-particle motion in the electromagnetic field of the star has been obtained. It is shown that two streams of charged particles escape from the star surface. The electron stream moves along the magnetic axis. The electron stream is enveloped by proton-positron stream, which is generated by returning hard electrons accelerated by electromagnetic field of the star. 相似文献
12.
Since their discovery in Voyager images, the origin of the bright polar caps of Ganymede has intrigued investigators. Some models attributed the polar cap formation to thermal migration of water vapor to higher latitudes, while other models implicated plasma bombardment in brightening ice. Only with the arrival of Galileo at Jupiter was it apparent that Ganymede possesses a strong internal magnetic field, which blocks most of the plasma from bombarding the satellite's equatorial region while funneling plasma onto the polar regions. This discovery provides a plausible explanation for the polar caps as related to differences in plasma-induced brightening in the polar and the equatorial regions. In this context, we analyze global color and high resolution images of Ganymede obtained by Galileo, finding a very close correspondence between the observed polar cap boundary and the open/closed field lines boundary obtained from new modeling of the magnetic field environment. This establishes a clear link between plasma bombardment and polar cap brightening. High resolution images show that bright polar terrain is segregated into bright and dark patches, suggesting sputter-induced redistribution and subsequent cold trapping of water molecules. Minor differences between the location of the open/closed field lines boundary and the observed polar cap boundary may be due to interaction of Ganymede with Jupiter's magnetosphere, and our neglect of higher-order terms in modeling Ganymede's internal field. We postulate that leading-trailing brightness differences in Ganymede's low-latitude surface are due to enhanced plasma flux onto the leading hemisphere, rather than darkening of the trailing hemisphere. In contrast to Ganymede, the entire surface of Europa is bombarded by jovian plasma, suggesting that sputter-induced redistribution of water molecules is a viable means of brightening that satellite's surface. 相似文献
13.
The connection between the radio emission from “lightnings” produced by the absorption of high-energy photons from the cosmic
gamma-ray background in a neutron star magnetosphere and radio bursts from rotating ratio transients (RRATs) is investigated.
The lightning length reaches 1000 km; the lightning radius is 100 m and is comparable to the polar cap radius. If a closed
magnetosphere is filled with a dense plasma, then lightnings are efficiently formed only in the region of open magnetic field
lines. For the radio emission from a separate lightning to be observed, the polar cap of the neutron star must be directed
toward the observer and, at the same time, the lightning must be formed. The maximum burst rate is related to the time of
the plasma outflow from the polar cap region. The typical interval between two consecutive bursts is ∼100 s. The width of
a single radio burst can be determined both by the width of the emission cone formed by the lightning emitting regions at
some height above the neutron star surface and by a finite lightning lifetime. The width of the phase distribution for radio
bursts from RRATs, along with the integrated pulse width, is determined by the width of the bundle of open magnetic field
lines at the formation height of the radio emission. The results obtained are consistent with the currently available data
and are indicative of a close connection between RRATs, intermittent pulsars, and extreme nullers. 相似文献
14.
Gravitational lensing properties and the influence of the electric charge on the light curves of a slowly rotating neutron star whose exterior is described by the Reissner-Nordström metric are considered. The polar cap emission model is assumed. No effect of the magnetosphere except for its possible contribution to the total charge is taken into account. In general, the lensing effect is reduced by the charge and the light curves become more similar to those typical in flat space rather than to the Schwarzschild spacetime. 相似文献
15.
Within the framework of the partially screened inner acceleration region the relationship between the X-ray luminosity and
the circulational periodicity of drifting subpulses is derived. This relationship is quite well satisfied in pulsars for which
an appropriate radio and X-ray measurements exist. A special case of PSR B0943+10 is presented and discussed. The problem
of formation of a partially screened inner acceleration region for all pulsars with drifting subpulses is also considered.
It is argued that an efficient inner acceleration region just above the polar cap can be formed in a very strong and curved
non-dipolar surface magnetic field.
We acknowledge the support of the Polish State Committee for scientific research under Grant P03D 029 26. G.M. was partially
supported by Georgian NSF grant ST06/4-096. 相似文献
16.
A. N. Timokhin 《Astrophysics and Space Science》2007,308(1-4):345-351
Pulsar “standard model”, that considers a pulsar as a rotating magnetized conducting sphere surrounded by plasma, is generalized
to the case of oscillating star. We developed an algorithm for calculation of the Goldreich-Julian charge density for this
case. We consider distortion of the accelerating zone in the polar cap of pulsar by neutron star oscillations. It is shown
that for oscillation modes with high harmonic numbers (l,m) changes in the Goldreich-Julian charge density caused by pulsations of neutron star could lead to significant altering of
an accelerating electric field in the polar cap of pulsar. In the moderately optimistic scenario, that assumes excitation
of the neutron star oscillations by glitches, it could be possible to detect altering of the pulsar radioemission due to modulation
of the accelerating field.
This work was partially supported by RFBR grant 04-02-16720, and by the grants N.Sh.-5218.2006.2 and RNP-2.1.1.5940. 相似文献
17.
Yu. A. Rylov 《Astrophysics and Space Science》1984,107(2):381-401
A self-consistent pulsar magnetospheric model with electron-positron pair production is considered. Unlike conventional models, the primary particles (electrons) are accelerated towards the neutron star and their curvature radiation towards a star generates electron-positron plasma near the neutron star. Inside an outflow channel, the generated plasma flows away from the pulsar magnetosphere. A part of the plasma electrons returns and, being accelerated towards the star, regenerate the plasma by their curvature radiation. It is shown that plasma production near the star causes an appearance of positron and electron equatorial belts. The plasma concentration and the flux of the returning electrons are estimated. The portion of the energy entering into the pulsar magnetosphere and its dependence on pulsar parameters are estimated. 相似文献
18.
D. N. Sob’yanin 《Astronomy Letters》2016,42(11):745-751
The electromagnetic field in a magnetized neutron star and the underlying volume charges and currents are found. A general case of a rigidly rotating neutron star with infinite conductivity, arbitrary distribution of the internal magnetic field, arbitrarily changing angular velocity, and arbitrary surface velocity less than the velocity of light is considered. Quaternions are used to describe rotation and determine the magnetic field. It is shown that the charge density is not equal to and can exceed significantly the common Goldreich–Julian density. Moreover, corrections to the magnetic field due to stellar rotation are zero. For a rotating neutron star, twisting magnetic field lines causes charge accumulation and current flows. This fact shows a possible link between changing internal magnetic field topology and observed activity of neutron stars. 相似文献
19.
Pulsars are presently believed to be rotating neutron stars with large frozen-in magnetic fields normally assumed to be dipole fields. It has been shown that such a star must possess a magnetosphere if it rotates sufficiently rapidly. By assuming that the magnetic field is dipolar, and unaffected by the trapped particles in the magnetosphere, and that the field dipole axis is parallel to the rotation axis, Goldreich and Julian determined many of the properties of the magnetosphere. In this paper is given a self-consistent model of the closed field lines of a pulsar magnetosphere. Using this model, it is shown that, close to the star, the above assumptions of Goldreich and Julian are justified. Their results are extended to the oblique rotator as well as to stars with magnetic multipoles of arbitrary order and arbitrary orientation.Supported in part by the U.S. Atomic Energy Commission under Grant 2171T. 相似文献