共查询到20条相似文献，搜索用时 31 毫秒
1.
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
2.
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
3.
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
4.
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
5.
Yu. A. Rylov 《Astrophysics and Space Science》1985,117(1):5-34
The self-consistent balanced pulsar magnetosphere of a magnetic neutron star with aligned magnetic and rotational axes is considered. It is shown that the magnetosphere consists of electron polar caps separated by empty space from a positron equatorial belt. The shape of the cold polar caps at a large distance from the star is calculated. It is shown that the cap shape at a large distance is independent of the magnetospheric structure near the neutron star. The shape of the equatorial belt is calculated. It is shown that a part of the equatorial belt rotates differentially, and its angular velocity is larger than that of the star (superrotation). It is shown that under certain conditions the space charge density of the belt can be very large. In principle, the formation of a surface charge placed in vacuum on a magnetic surface is possible. Magnetospheric vibrations are considered. A connection is established between drifting subpulses and the equatorial belt superrotation and also between drifting subpulses and cap vibrations. The characteristic frequency of vibrations and the angular velocity of superrotation are estimated. 相似文献
6.
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
7.
8.
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
9.
The accretion-induced neutron star (NS) magnetic field evolution is studied through considering the accretion flow to drag the field lines aside and dilute the polar-field strength, and as a result the equatorial field strength increases, which is buried inside the crust on account of the accretion-induced global compression of star crust. The main conclusions of model are as follows: (i) the polar field decays with increase in the accreted mass; (ii) the bottom magnetic field strength of about 108 G can occur when the NS magnetosphere radius approaches the star radius, and it depends on the accretion rate as ; and (iii) the NS magnetosphere radius decreases with accretion until it reaches the star radius, and its evolution is little influenced by the initial field and the accretion rate after accreting ∼0.01 M⊙ , which implies that the magnetosphere radii of NSs in low-mass X-ray binaries would be homogeneous if they accreted the comparable masses. As an extension, the physical effects of the possible strong magnetic zone in the X-ray NSs and recycled pulsars are discussed. Moreover, the strong magnetic fields in the binary pulsars PSR 1831−00 and PSR 1718−19 after accreting about 0.5 M⊙ in the binary-accretion phase, 8.7 × 1010 and 1.28 × 1012 G , respectively, can be explained through considering the incomplete frozen flow in the polar zone. As an expectation of the model, the existence of the low magnetic field (∼3 × 107 G) NSs or millisecond pulsars is suggested. 相似文献
10.
C. G. Campbell 《Monthly notices of the Royal Astronomical Society》2005,359(3):835-845
The interaction is investigated between a white dwarf magnetosphere and a red dwarf secondary star in an asynchronous AM Herculis binary. The poloidal magnetic field diffuses into the secondary and shearing motions, due to differential rotation between the star and the magnetosphere, generate azimuthal field. The effects of diffusion and field advection caused by a poloidal flow induced by magnetospheric motions are calculated. Outward radial motions reduce the amount of field penetration and limit the stellar magnetic torque at higher degrees of asynchronism. A resonance torque curve results, similar to the case of a precessing magnetic field with vacuum surroundings. Inward motions in the secondary increase field penetration, allowing the torque to reach higher values for larger degrees of asynchronism. 相似文献
11.
A. I. Tsygan 《Astronomy Letters》2017,43(12):820-830
The X-ray luminosity and temperature of the polar cap heated by the back flux of positrons from a radio pulsar with a period P ～ 1 s and a magnetic field B ~ 1012 G have been estimated. An additional source of X-ray emission—a thin, hotter semiring on the polar-cap periphery—is shown to also exist. It is heated by the back flux of electrons from the light cylinder. Furthermore, the electric field near the hot semiring accelerates the ions of the surface layer that leave the neutron-star magnetosphere. The semiring area is smaller than the polar-cap area approximately by a factor of 100, i.e., at the same luminosity the temperature is higher by a factor of 3. The observed X-ray emission from old radio pulsars is the emission from thin hot polar-cap semirings. The emission from the polar caps themselves is strongly attenuated by interstellar absorption. 相似文献
12.
Chu W. Kwang-Hua 《Astrophysics and Space Science》2018,363(9):184
Using verified transition state theory and quantum plasticity theory we calculate the temperature-dependent shear (strain) rates as well as temperature-dependent (shear) viscosity considering magnetically driven plastic flows in the neutron star (like CXOU J164710.2-455216) crust. Our numerical results which are based on previous works like the critical shear stress as well as the minimum shear (strain) rate of crust (around \(1~\mbox{rad}/\mbox{year}\)) demonstrate that a plastic deformation of the neutron star crust could induced a very slight twist (or shear) in the external magnetic field. We then extend Lander’s calculation of magnetospheric twist to slip-flow cases that will generated currents in the magnetosphere of the magnetar, say, CXOU J164710.2-455216 in Westerlund 1. The latter is believed to be the direct cause of the observed X-ray outburst by Muno et al. once we examine the associated energy scales for corresponding magnetic fields considering the age or history of CXOUJ164710.2-455216 which can be estimated from available measurements or observations. Our results and analysis of relevant energy scales confirm the onset of the soft gamma repeater outburst is controlled by magnetospheric dissipation induced by the plastic motions of the crust. 相似文献
13.
U. Geppert 《Journal of Astrophysics and Astronomy》2017,38(3):46
The magnetic and thermal evolution of neutron stars is a very complex process with many non-linear interactions. For a decent understanding of neutron star physics, these evolutions cannot be considered isolated. A brief overview is presented, which describes the main magneto–thermal interactions that determine the fate of both isolated neutron stars and accreting ones. Special attention is devoted to the interplay of thermal and magnetic evolution at the polar cap of radio pulsars. There, a strong meridional temperature gradient is maintained over the lifetime of radio pulsars. It may be strong enough to drive thermoelectric magnetic field creation which perpetuate a toroidal magnetic field around the polar cap rim. Such a local field component may amplify and curve the poloidal surface field at the cap, forming a strong and small scale magnetic field as required for the radio emission of pulsars. 相似文献
14.
Jin Zhang Jin-Ming Bai Liang Chen Enwei Liang 《Journal of Astrophysics and Astronomy》2011,32(1-2):193-196
The observed broadband spectral energy distributions (SEDs) of 22 hot spots and 45 knots are modelled with single-zone lepton models. Considering the sources at rest, the X-rays of some hot spots can be explained by the SSC model with magnetic field being consistent with the equipartition magnetic field in magnitude of order 1, but at the same time an unreasonably low magnetic field is required to model the X-rays for all knots. When considering the relativistic bulk motion of the sources, the IC/CMB model well explains the X-ray emission for most of them under the equipartition condition. We show that the ratio of observational luminosity R L is tentatively correlated with the co-moving equipartition magnetic field $B_{\rm eq}^{\prime}$ and the beaming factor ??. These facts suggest that the observational differences of the X-rays from the knots and hot spots may be mainly due to the differences in the Doppler boosting effect and the co-moving magnetic field of the two kinds of source. 相似文献
15.
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
16.
The production of pairs of magnetic monopoles-antimonopoles should be expected in the interactions of the high energy particles accelerated by pulsars. In the frame of the Sturrock model, the interactions of the very high energy protons emitted from the polar caps with the secondary electrons can be a source of magnetic monopoles. It may be the dominating process in very young pulsars such as the Crab pulsar. In the polar gap model of Ruderman and Sutherland, magnetic monopoles can be created by the electrons accelerated across the cap and interacting with the neutron star crust or by the negatons and positrons interacting head-on inside the sparks.Half of these monopoles are accelerated towards the interstellar medium by the pulsar magnetic field and the others are likely to be trapped inside the neutron star crust. This leads to a decrease in the pulsar magnetic field which would imply that the characteristic age
may not give the true age of the pulsar This can be related to the discrepancy between and the real age of the Crab pulsar and the kinematical ages obtained from the measurement of the proper motion of some pulsars. Furthermore, the trapping of magnetic monopoles close under the surface of the neutron star perturbates the pulsar electrodynamics. To have such observable effects, it is shown that the cross-sections for the magnetic monopoles production can be several orders of magnitude smaller than the upper limits so far derived from cosmic rays or accelerator data.The possibility that the magnetic monopoles, accelerated outwards, are responsible for the highest energy extensive air showers, is considered.The production of an avalanche of secondary monopoles, due to acceleration by the magnetic field in the neutron star crust, is possible and the consequences of this process are considered. 相似文献
17.
18.
We apply the model of flux expulsion from the superfluid and superconductive core of a neutron star, developed by Konenkov & Geppert, both to neutron star models based on different equations of state and to different initial magnetic field structures. Initially, when the core and the surface magnetic field are of the same order of magnitude, the rate of flux expulsion from the core is almost independent of the equation of state, and the evolution of the surface field decouples from the core field evolution with increasing stiffness. When the surface field is initially much stronger than the core field, the magnetic and rotational evolution resembles that of a neutron star with a purely crustal field configuration; the only difference is the occurrence of a residual field. In the case of an initially submerged field, significant differences from the standard evolution only occur during the early period of the life of a neutron star, until the field has been re-diffused to the surface. The reminder of the episode of submergence is a correlation of the residual field strength with the submergence depth of the initial field. We discuss the effect of the re-diffusion of the magnetic field on the difference between the real and the active age of young pulsars and on their braking indices. Finally, we estimate the shear stresses built up by the moving fluxoids at the crust–core interface and show that these stresses may cause crust cracking, preferentially in neutron stars with a soft equation of state. 相似文献
19.
V. G. Kryvdyk 《Kinematics and Physics of Celestial Bodies》2009,25(6):277-301
We investigate a transformation of a magnetic field and plasma in nonhomogeneous magnetospheres of collapsing stars with a
dipole initial magnetic field and certain initial energy distributions of particles in the magnetosphere as the power low,
relativistic Maxwell and Boltzmann. The betatron mechanism of the charged particles acceleration in a collapsing star’s magnetosphere
is considered. When a magnetized star is compressed in the stage of the gravitational collapse, the magnetic field increases
strongly. This variable magnetic field generates a vortical electric field. Our calculations show that this electric field
will accelerate charged particles up to relativistic velocities. Thus, collapsing stars may be sources of high energy cosmic
rays in our galaxy as in others. The acceleration of particles during the collapse happens mostly in polar regions of the
magnetosphere that leads to polar relativistic streams (jets) formation. When moving in a magnetic field, these particles
will generate nonthermal electromagnetic radiation in a broad electromagnetic wavelength band from radioto gamma rays. Thus,
in the stage of the gravitational collapse, relativistic jets are formed in stellar magnetospheres. These jets are powerful
sources of the nonthermal electromagnetic radiation. 相似文献
20.
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