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1.
The influence of an axisymmetric magnetic field on the intensity, spectrum, and shape of a pulse of gamma-ray curvature radiation from the polar regions of a radio pulsar is investigated. The pulsar is considered in a Goldreich-Julian model with a free-electron emission from the neutron-star surface. The influence on the curvature radiation of variations of both the curvature of the magnetic field lines and the electric field due to the nondipolarity of the magnetic field are investigated. The presence of even modest nondipolarity (less than 10%) can lead to a sharp drop in the intensity of the gamma-ray curvature radiation, while the intensity of the X-ray curvature radiation (photon energies <100 keV) is affected only weakly. 相似文献
2.
We consider the influence of a non-dipolar magnetic field on the gamma-ray emission from the polar regions of a radio pulsar. The pulsar is treated in a Goldreich-Julian model with a free flow of charge from the surface of the neutron star. When finding the intensity of the gamma-ray radiation of the pulsar tube, both curvature gamma-ray radiation from the primary electrons and non-resonance inverse Compton scattering of thermal photons from the polar cap on primary electrons are taken into account. When finding the height of the upper plate of the pulsar diode, we included only positrons created by the curvature radiation of primary electrons. We assumed that the polar cap is heated by the return positron current. The influence on the gamma-ray emission of variations in both the radius of curvature of the magnetic force lines and in the electric field due to the non-dipolarity of the magnetic field were taken into account. The presence of even weak non-dipolarity of the magnetic field leads to a sharp decrease in the intensity of the gamma-ray emission from the pulsar tube at energies 1–100 MeV, while the intensity of the inverse Compton radiation (at energies 1–100 GeV) varies only relatively weakly. 相似文献
3.
《International Geology Review》2012,54(2):191-195
The author proposes a method of telluric-magnetic mapping, profiling, and exploration. The profiling involves recording of short-period variations in the telluric current and the magnetic field (MTP) and an areal (MVR), similar to the above. The method can be used on any segment of the crust, especially with newly designed, highly sensitive short-period magnetometer. The magnetic fields of telluric currents are measured by means of a four-channel oscillograph controlled from a panel in which switches are incorporated. The magnetic fields of the telluric current are measured at two points, since the automatic switching arrangement permits a procedure identical with the measurements in the telluric current. Amplitudes and periods of almost sinusoidal waves are measures of the chords of the elliposidal electric and magnetic fields. Analysis of magnetic field mapping and its results are given. The author feels that the telluric-magnetic profiling should replace direct telluric voltage measurements in many regions because of its economics. It gives precise data on the structure of the sedimentary cover. Telluric-exploration will open up entirely new possibilities in permafrost zones and the method will be substantially more efficient than direct telluric measurements. — A.W. Bellais 相似文献
4.
We consider the properties of electric and magnetic fields in vacuum in the neighborhood of static, spherically symmetric
wormholes. Although certain aspects of this problem have been considered before, some important features remained undiscovered.
We study in detail the properties of electric and magnetic fields in the case of quasi-adiabatic motion of field sources near
an Ellis-Bronnikov wormhole and the passage of such sources through the wormhole. An exact solution is found in closed form
for a wormhole immersed in a magnetic field that is homogeneous at infinity, as well as an exact solution for a dipolar field
without sources. The properties of electromagnetic fields are important for possible observational manifestations of wormholes
in astrophysics. 相似文献
5.
The effect of curvature of open magnetic-field tubes on the death lines of radio pulsars is studied. The solution is obtained in the framework of a Goldreich-Julian model for both dipolar and asymmetric magnetic fields. The tube-axis curvature can shift the death line appreciably toward either longer or shorter periods. If the field is dipolar and gamma rays are generated by the inverse Compton effect, the formation of secondary plasma is more efficient near the death line. In the case of an asymmetric magnetic field, the generation of radio emission beyond the tube of open field lines is possible. 相似文献
6.
The effect of the radius of the tube of open magnetic-field lines on the gamma-ray curvature radiation from the polar regions of a radio pulsar with a non-dipolar magnetic field is analyzed. The pulsar is considered in a polar-cap model with free electron emission from the neutron-star surface. The effect of the non-dipolar magnetic field on the radius of curvature of the field lines and the field intensity is taken into account. In connection with the creation of electron-positron pairs, we take into account only the birth of pairs by curvature radiation in the magnetic field. The small non-dipolarity of the field enables the radio pulsar not to turn off, even after a considerable decrease in the pulsar-tube radius. For instance, with a 20% non-dipolarity (ν = 0.2), a pulsar with B = 1013 G and P = 0.5 s can still operate even for a fivefold decrease in the pulsar-tube radius. A maximum is observed in the dependence of the electrostatic potential in the diode on the non-dipolarity parameter ν at ν ～ 0.5–0.7. The pulse profile in non-thermal X-ray emission for ν ～ 0.5–0.7 may look virtually the same as for ν ～ 0.1–0.2. Decreases in the pulsar-tube radius could be due to a structure of currents in the magnetosphere that results in the pulsar diode on the neutron-star surface occupying only a small fraction of the pulsar tube, with the remainder of the tube containing an outer annular gap. The pulsar-tube size is also affected by the presence of a circum-pulsar disk. A change in the pulsar-tube radius could also be due to an external magnetic field, associated with either a magnetic white dwarf or a circum-pulsar disk. 相似文献
7.
An approximate method for calculating the returning positron flux in the polar-cap regions of a radio pulsar is proposed. The pulsar is considered in the Goldreich-Julian model for a regime of free-electron emission from the neutron-star surface in the region of open lines of the dipolar magnetic field. Calculations have been done for the case when the dipolar magnetic moment is aligned with the star's rotational axis. The acceleration of primary electrons is assumed to occur near the neutron-star surface on scales comparable to the transverse radius of the tube of open field lines. The generation of electron-positron pairs by curvature radiation of the primary electrons is taken into account. A considerable contribution to the returning flux is made by the region where the electric field is screened by the electron-positron plasma. 相似文献
8.
The flare source of thermal X-rays above a magnetic arch in the corona arises from the dissipation of the magnetic energy
of the current sheet formed at the reconnection of magnetic-field lines. The sources of hard X-rays emitted from the footpoints
of the magnetic arch are beams of electrons accelerated in field-aligned currents induced by the Hall electric field generated
in the current sheet. Both the hard X-rays detected above the active region and the type III radio emission are radiated by
electrons accelerated in the field-aligned currents induced by Alfven waves. The solar cosmic rays are emitted promptly at
the instant of the flare. It is important that the Lorentz electric field accelerates protons along the singular magnetic
X line. The relativistic protons propagate along the interplanetary magnetic field. These protons have exponential spectra,
typical for acceleration occurring in current sheets. A mechanism that is relevant for the generation of delayed cosmic rays,
which demonstrate significant anisotropy and a power-law spectrum with γ ∼5, is also discussed. 相似文献
9.
A mechanism for the acceleration of electrons in the ionosphere of Io due to the moon's motion through the Jovian magnetic field and the presence of Io's ionosphere is considered. Attention is drawn to the important role of the anisotropic conductivity of the ionosphere, which results in the formation of a longitudinal (with respect to the planetary magnetic field) component of the charge-separation electric field. Owing to this anisotropy, the electric field induced by the motion of Io, Ei, produces in Io's ionosphere not only a Pedersen electrical current along Ei but also a Hall current that is approximately perpendicular to the moon's surface in the “upstream” and “downstream” parts of the ionosphere. However, this current cannot be closed through the surface, leading to the formation of a powerful charge-separation field in Io's ionosphere. This field has a component parallel to the magnetic field, with an amplitude comparable to that of the induced electric field. Electron runaway along the magnetic field is also considered, and the occurrence of “active longitudes” and preferred locations for the sources of decametric radio emission in the northern hemisphere of Jupiter are interpreted. The characteristic energies and fluxes of the accelerated electrons injected into Io's flux tube are estimated. The energy of these electron fluxes is sufficient to produce the electromagnetic radiation observed from Io's magnetic tube. 相似文献
10.
V. V. Prudskikh 《Astronomy Reports》2013,57(6):440-447
The stability of magnetohydrodynamic oscillations in a protostellar disk with a toroidal magnetic field is analyzed. It is shown that, apart from the aperiodic magnetorotational instability, two other types of periodic instabilities of non-axisymmetric perturbations can exist. The simultaneous presence of azimuthal and vertical components of the wave vector are necessary for these to exist. One instability is due to the inductive winding-up of the azimuthal magnetic field of the wave, and the other arises when the field amplitude is increased by a comoving Hall wave, transferring magnetic field into a region of enhanced field intensity. The bandwidths of the unstable wave numbers are analyzed as a function of the Hall current, the β parameter of a plasma, and the angle between the direction of wave propagation and the plane of the disk. Regions in the accretion disks typical of T Tauri stars are indentified where these instabilities could be most active. 相似文献
11.
New data for the energy and location of the hard-emission centers of a solar flare agree with an electrodynamic model of a solar flare based on the idea of the accumulation of free magnetic energy in the field of a current sheet. Three-dimensional MHD simulations are used to show that the energy stored in the preflare magnetic field of the current sheet is sufficient for the development of a flare and a coronal mass ejection. The flare and coronal mass ejection result from the explosive decay of the current sheet. The position of the brightness-temperature maximum of the radio emission during the flare coincides with the maximum of the current in the current sheet. The exponential spectrum of relativistic protons generated during the flare is consistent with acceleration by the electric field during the current-sheet decay. 相似文献
12.
We have developed a three-dimensional numerical model and applied it to simulate plasma flows in semi-detached binary systems
whose accretor possesses a strong intrinsic magnetic field. The model is based on the assumption that the plasma dynamics
are determined by the slow mean flow, which forms a backdrop for the rapid propagation of MHD waves. The equations describing
the slow motion of matter were obtained by averaging over rapidly propagating pulsations. The numerical model includes the
diffusion of magnetic field by current dissipation in turbulent vortices, magnetic buoyancy, and wave MHD turbulence. A modified
three-dimensional, parallel, numerical code was used to simulate the flow structure in close binary systems with various accretor
magnetic fields, from 105 to 108 G. The conditions for the formation of the accretion disk and the criteria distinguishing the two types of flow corresponding
to intermediate polars and polars are discussed. 相似文献
13.
The reverse positron current flowing through the inner gap of an old radio pulsar in the presence of a small-scale magnetic field is found. Computations for the case of both strong and weak screening of the longitudinal electric field by the electron–positron plasma are presented. 相似文献
14.
时间谱电阻率法可行性初探 总被引：7，自引：2，他引：7
基于层状导电和可极化大地表面，电偶源电场水平分量和磁场垂直分量时间导数瞬变响应的计算结果，分析和概括了水平分量和时间导数阶跃响应随电磁（ＥＭ）和激电（ＩＰ）效应的变化规律。并在此基础上，初步探讨和肯定了建立时间谱电阻率法的可能性。 相似文献
15.
分析了水平电偶源与垂直磁偶源的电磁场在半空间大地中的分布特点,指出观测各场分量的合适地面部位。为了定性解释,一般将场分量计算为单分量视电阻率或比值视电阻率;做定量解释时,可直接采用场强进行反演,以减小换算误差。基于当前电偶源与磁偶源的发射功率和电磁场衰减规律,在实际应用中,水平电偶源可探测更大深度(<3 000 m),垂直磁偶源探测浅部(<500 m)。 相似文献
16.
The structure and magnitude of the electric field created by a rotating accretion disk with a poloidal magnetic field is found for the case of a vacuum approximation along the axis. The accretion disk is modeled as a torus filled with plasma and a frozen-in magnetic field. The dimensions and location of the maximum electric field as well as the energy of the accelerated particles are found. The gravitational field is assumed to be weak. 相似文献
17.
矿物磁性特征在金矿床形成及成矿预测中的作用 总被引：3，自引：1，他引：2
金矿床形成和成矿预测一直为国内外学者所关注。随绿岩带金矿、暗色岩易富金及赤铁矿总含有大粒金等不断地被发现,指示矿物磁性对金矿床形成有一定的控制作用。1)金粒级的大小与磁体间作用力的强弱呈正比,磁力的大小与两磁体间距离的平方呈反比,这正、反比规律进一步解析绿岩带富金机理和强、弱磁性岩石富金条件的差别。2)电流在金、黄铁矿和磁黄铁矿等附近每一点都能产生磁化场(H场)和磁通密度(B场),H场和B场的大小与不同成矿介质具有一定的正比例关系,按此比例可追踪含矿流体形成过程和富金条件。3)根据矿物磁性特征,建立了矿物磁力晕、矿物磁性矢量等找矿标志。4)除温度和压力等因素外,矿物磁性特征应视为金矿床形成和预测主要条件之一。 相似文献
18.
Using observational data obtained with the Yohkoh, SOHO, and TRACE satellites, it is shown that the three-dimensional structure of the large solar flare of July 14, 2000 was determined by the topology of the large-scale magnetic field of the active region giving rise to the flare. The locations and shapes of chromospheric ribbons and brightness centers on these ribbons are explained. The observed behavior of the flare is attributed to rapid magnetic reconnection in the corona. The electric field accelerating particles in the reconnecting current sheets is estimated. 相似文献
19.
The evolution of a system of electrons with a given initial distribution in an external magnetic field is considered. An equation describing the evolution of the electron distribution function in a uniform magnetic field is derived for the case of arbitrarily relativistic electrons, and an exact solution to this equation is found. Asymptotics of this solution corresponding to the cases of synchrotron radiation and relativistic dipole radiation are calculated, and the evolution of the radiation spectra for these limiting cases is analyzed. The curvature of the magnetic field lines is taken into account phenomenologically, which demonstrates the presence of an exponential dependence in the case of synchrotron radiation. 相似文献
20.
A. V. Getling 《Astronomy Reports》2001,45(7):569-576
The well-known model that attributes the formation of a bipolar sunspot group to the emergence of a flux tube disagrees sharply with the usual observed pattern of phenomena. At the same time, the observed patterns can be accounted for quite convincingly in terms of local magnetic-field amplification due to cellular convective motions of the solar plasma. In this study, magnetoconvection in a plane horizontal fluid layer is simulated numerically in the framework of the fully nonlinear, three-dimensional problem. A weak horizontal magnetic field and weak cellular flow are assumed to be present initially. Convection is shown to be capable of producing bipolar magnetic configurations of the strongly amplified magnetic field. Indications of magnetic freezing of the flow in the cell are found. The action of the amplification mechanism under study may be controlled by the large-scale toroidal magnetic field of the Sun. 相似文献