共查询到20条相似文献，搜索用时 15 毫秒
1.
Michelle B. Larson † Bennett Link 《Monthly notices of the Royal Astronomical Society》2002,333(3):613-622
Many radio pulsars exhibit glitches wherein the star's spin rate increases fractionally by ∼10−10 –10−6 . Glitches are ascribed to variable coupling between the neutron star crust and its superfluid interior. With the aim of distinguishing among different theoretical explanations for the glitch phenomenon, we study the response of a neutron star to two types of perturbations to the vortex array that exists in the superfluid interior: (1) thermal motion of vortices pinned to inner crust nuclei, initiated by sudden heating of the crust, (e.g., a starquake), and (2) mechanical motion of vortices (e.g., from crust cracking by superfluid stresses). Both mechanisms produce acceptable fits to glitch observations in four pulsars, with the exception of the 1989 glitch in the Crab pulsar, which is best fitted by the thermal excitation model. The two models make different predictions for the generation of internal heat and subsequent enhancement of surface emission. The mechanical glitch model predicts a negligible temperature increase. For a pure and highly conductive crust, the thermal glitch model predicts a surface temperature increase of as much as ∼2 per cent, occurring several weeks after the glitch. If the thermal conductivity of the crust is lowered by a high concentration of impurities, however, the surface temperature increases by ∼10 per cent about a decade after a thermal glitch. A thermal glitch in an impure crust is consistent with the surface emission limits following the 2000 January glitch in the Vela pulsar. Future surface emission measurements coordinated with radio observations will constrain glitch mechanisms and the conductivity of the crust. 相似文献
2.
We present a model of a freely precessing neutron star, which is then compared against pulsar observations. The aim is to draw conclusions regarding the structure of the star, and to test theoretical ideas of crust–core coupling and superfluidity. We argue that, on theoretical grounds, it is likely that the core neutron superfluid does not participate in the free precession of the crust. We apply our model to the handful of proposed observations of free precession that have appeared in the literature. Assuming crust-only precession, we find that all but one of the observations are consistent with there being no pinned crustal superfluid at all; the maximum amount of pinned superfluid consistent with the observations is about 10−10 of the total stellar moment of inertia. However, the observations do not rule out the possibility that the crust and neutron superfluid core precess as a single unit. In this case the maximum amount of pinned superfluid consistent with the observations is about 10−8 of the total stellar moment of inertia. Both of these values are many orders of magnitude less than the 10−2 value predicted by many theories of pulsar glitches. We conclude that superfluid pinning, at least as it affects free precession, needs to be reconsidered. 相似文献
3.
W. Z. Zou N. Wang R. N. Manchester J. O. Urama G. Hobbs Z. Y. Liu J. P. Yuan 《Monthly notices of the Royal Astronomical Society》2008,384(3):1063-1068
Six glitches have been recently observed in the rotational frequency of the young pulsar PSR B1737−30 (J1740−3015) using the 25-m Nanshan telescope of Urumqi Observatory. With a total of 20 glitches in 20 yr, it is one of the most frequently glitching pulsars of the ∼1750 known pulsars. Glitch amplitudes are very variable with fractional increases in rotation rate ranging from 10−9 to 10−6 . Interglitch intervals are also very variable, but no relationship is observed between interval and the size of the preceding glitch. There is a persistent increase in , opposite in sign to that expected from slowdown with a positive braking index, which may result from changes in the effective magnetic dipole moment of the star during the glitch. 相似文献
4.
The gravitational radiation from millisecond pulsars owing to glitches in their angular velocity is examined. It is assumed
that the energy transferred from interior superfluid regions to the crust of a neutron star is converted into gravitational
wave energy by damping oscillations of the matter in the star. The gravitational wave intensity and amplitude are calculated
for fourteen millisecond pulsars. Gravitational radiation can explain the observed spin-down of millisecond pulsars and an
estimate is given for the magnetic field at which the proposed mechanism predominates in the spin-down of these pulsars.
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Translated from Astrofizika, Vol. 51, No. 3, pp. 479–486 (August 2008). 相似文献
5.
射电脉冲星周期跃变被认为是研究中子星内部结构和状态的极好探针。脉冲星高频巡天发现了一批年青脉冲星,脉冲星周期跃变的观测研究也有了飞快进展。至少发现了２５颗有跃变现象的脉冲星（简称跃变脉冲星）和７６次跃变事件。ＰＳＲＪ０８３５－４５１０是目前已有跃变脉冲星活动参数最高的,ＰＳＲＪ１３４１－６２２２０的跃变活动最频繁,而ＰＳＲＪ１６１４－５０４７在１９９５年发生的跃变是规模最大的,不同脉冲星的跃变事件 相似文献
6.
A theory of the relaxation of pulsar angular velocity is compared with observational data for the first eight glitches of the Vela pulsar. The inverse problem of the theory of relaxation is considered and solutions of this problem in the regions of exponential and linear relaxation are found. General features in the distribution of neutron vortices in these regions immediately after a glitch are determined. It is shown that these properties may be related to the size of the glitch in pulsar angular velocity. 相似文献
7.
The loss of angular momentum through gravitational radiation, driven by the excitation of r-modes, is considered for neutron stars that have rotation frequencies lower than the associated critical frequency. We find that for reasonable values of the initial amplitudes of such pulsation modes of the star, being excited at the event of a glitch in a pulsar, the total post-glitch losses correspond to a negligible fraction of the initial rise of the spin frequency in the case of Vela and older pulsars. However, for the Crab pulsar the same effect would result, within a few months, in a decrease in its spin frequency by an amount larger than its glitch-induced frequency increase. This could provide an explanation for the peculiar behaviour observed in the post-glitch relaxations of the Crab pulsar. 相似文献
8.
Geraint F. Lewis Rodrigo A. Ibata Sara L. Ellison Bastien Aracil Patrick Petitjean Max Pettini Raghunathan Srianand 《Monthly notices of the Royal Astronomical Society》2002,334(1):L7-L10
PSR J1806−2125 is a pulsar discovered in the Parkes multibeam pulsar survey with a rotational period of 0.4 s and a characteristic age of 65 kyr. Between MJDs 51462 and 51894 this pulsar underwent an increase in rotational frequency of Δ ν / ν ≈16×10-6 . The magnitude of this glitch is ∼2.5 times greater than any previously observed in any pulsar and 16 times greater than the mean glitch size. This Letter gives the parameters of the glitch and compares its properties with those of previously observed events. The existence of such large and rare glitches offers new hope for attempts to observe thermal X-ray emission from the internal heat released following a glitch, and suggests that pulsars which previously have not been observed to glitch may do so on long time-scales . 相似文献
9.
P. B. Jones 《Monthly notices of the Royal Astronomical Society》2001,321(1):167-175
Formation enthalpies are calculated for a number of point-defect structures in solid neutron star matter at densities above the neutron-drip threshold. The enthalpies obtained show that an amorphous heterogeneous solid phase is formed at temperatures in a glass transition region, and is likely to persist as the star cools. Its structural differences from the homogeneous body-centred cubic lattice previously assumed make it necessary to reconsider predictions of neutron-star magnetic field evolution, and severely limit the role of conventional superfluid neutron vortex pinning in the interpretation of pulsar glitch phenomena. 相似文献
10.
Kouichi Hirotani Shinpei Shibata 《Monthly notices of the Royal Astronomical Society》2001,325(3):1228-1240
We investigate a stationary particle acceleration zone in the outer magnetosphere of an obliquely rotating neutron star. The charge depletion as a result of global current causes a large electric field along the magnetic field lines. Migratory electrons and/or positrons are accelerated by this field to radiate curvature gamma-rays, some of which collide with the X-rays to materialize as pairs in the gap. As a result of this pair-production cascade, the replenished charges partially screen the electric field, which is self-consistently solved together with the distribution of particles and gamma-rays. If no current is injected at either of the boundaries of the accelerator, the gap is located around the so-called null surface, where the local Goldreich–Julian charge density vanishes. However, we find that the gap position shifts outwards (or inwards) when particles are injected at the inner (or outer) boundary. We apply the theory to the seven pulsars whose X-ray fields are known from observations. We show that the gap should be located near to or outside of the null surface for the Vela pulsar and PSR B1951+32, so that their expected GeV spectrum may be consistent with observations. We then demonstrate that the intrinsically large TeV flux from the outer gap of PSR B0540–69 is absorbed by the magnetospheric infrared photons, causing it to be undetectable. We also point out that the electrodynamic structure and the resultant GeV emission properties of millisecond pulsars are similar to young pulsars. 相似文献
11.
The forces acting on the solid crust of a differentially rotating neutron star are examined when a nonuniform excess of chemical
potential exists. The resultant of the external forces, a stress force, is expressed in terms of a centrifugal buoyancy force
and the deformation of the star’s crust under the action of this force is calculated. It is shown that there is a region within
the star where the resulting stresses lead to fracture of the crust when the difference in the angular velocities of the superfluid
and normal components reaches a critical value. The “centrifugal buoyancy” mechanism for generating a glitch is used to estimate
the parameters of glitches in the Vela pulsar.
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Translated from Astrofizika, Vol. 50, No. 2, pp. 183–197 (May 2007). 相似文献
12.
Simon Johnston David Galloway 《Monthly notices of the Royal Astronomical Society》1999,306(4):L50-L54
Using the standard equation for the slowdown of a neutron star, we derive a formula for the braking index via integration rather than the conventional differentiation. The new formula negates the need to measure the second time derivative of the rotation frequency, ν¨ . We show that the method gives similar braking indices for PSR B1509−58 and the Crab pulsar to those already in the literature. We point out that our method is useful for obtaining the braking indices of moderate-aged pulsars without the need for long, phase-connected timing solutions. We applied the method to 20 pulsars and discuss the implications of the results. We find that virtually all the derived braking indices are dominated by the effects of (unseen) glitches, the recovery from which corrupts the value of ν˙ . However, any real, large, positive braking index has implications for magnetic field decay and offers support to recent models of pulsar evolution. 相似文献
13.
Jones 《Monthly notices of the Royal Astronomical Society》1998,296(1):217-224
It is usually assumed that pulsar glitches are caused by the large-scale unpinning of superfluid neutron vortices in the solid crust of a neutron star and that vortex motion relative to the crust is highly dissipative at low velocities, owing to the excitation of long-wavelength Kelvin waves. The force per unit length acting on a vortex as a result of Kelvin wave excitation has been calculated for a polycrystalline structure using the free-vortex Green function. An approximate upper limit for the maximum pinning force has been obtained which, for the form of structure anticipated, is many orders of magnitude too small for consistency with the observed size and frequency of glitches. The corollary is that glitches do not originate in the crust: the necessary pinning may be given by the interaction between neutron and proton vortices in the liquid core of the star. 相似文献
14.
The effect of a neutron-proton vortex system on the rotation dynamics of neutron stars is examined. The dynamics of the motion of a two component superfluid system in the core of a neutron star yields an equation for the evolution of the pulsar's rotation period. The spin down of the star owing to energy release at the core boundary, which is associated with a contraction of the length of the neutron vortex as it moves radially and magnetic energy of the vortical cluster is released, is taken into account. Evolutionary curves are constructed for pulsars with different magnetic fields and stellar radii. For certain values of the coefficient of friction between the superfluid and normal components in the core of the neutron star, at the end of its evolution a radio pulsar may become an anomalous x-ray pulsar or a source of soft gamma radiation with a period on the order of 10 seconds. 相似文献
15.
Pulsar slow glitches in a solid quark star model 总被引：1，自引：0，他引：1
A series of five unusual slow glitches of the radio pulsar B1822–09 (PSR J1825–0935) was observed between 1995 and 2005. This is a phenomenon that is understood in a solid quark star model, and reasonable parameters for slow glitches are given in this paper. We propose that, because of increasing shear stress as the pulsar spins down, a slow glitch may occur, beginning with the collapse of a superficial layer of the quark star. This layer of material turns to viscous fluid at first, the viscosity of which helps to deplete the energy released from both the accumulated elastic energy and the gravitation potential. There is then a slow glitch. Numerical calculations show that the slow glitches that have been observed could be reproduced if the effective coefficient of viscosity is ∼102 cm2 s−1 and the initial velocity of the superficial layer is of the order of 10−10 cm s−1 in the coordinate rotating frame of the star. 相似文献
16.
J.O.Urama 《Monthly notices of the Royal Astronomical Society》2002,330(1):58-62
Large glitches were recently observed in the spin rates of two pulsars, B1046−58 and B1737−30. The glitches were characterized by fractional increases in rotation rate of 0.77 and 1.44×10−6 respectively. PSR B1737−30 is the most frequently glitching pulsar and this is the largest glitch so far observed from it. Most of the jump in the spin-down rate accompanying these glitches decayed away on short time-scales of a few days. For PSR B1737−30, there appears to be a cumulative shift in spin-down rate resulting from its frequent glitches. This probably accounts for its braking index of −4±2 suggested by the available data, while a value of 2.1±0.2 is obtained for B1046−58. 相似文献
17.
Raka Dona Ray Mandal Sushan Konar Mira Dey Jishnu Dey 《Monthly notices of the Royal Astronomical Society》2009,399(2):822-826
The single glitch observed in PSR B1821−24, a millisecond pulsar in M28, is unusual on two counts. First, the magnitude of this glitch is at least an order of magnitude smaller (Δν/ν∼ 10−11 ) than the smallest glitch observed to date. Secondly, all other glitching pulsars have strong magnetic fields with B ≳ 1011 G and are young, whereas PSR B1821−24 is an old recycled pulsar with a field strength of 2.25 × 109 G . We have earlier suggested that some of the recycled pulsars could actually be strange quark stars. In this work, we argue that the crustal properties of such a strange pulsar are just right to give rise to a glitch of this magnitude, explaining the scarcity of larger glitches in millisecond pulsars. 相似文献
18.
A recent laboratory experiment suggests that a Kelvin–Helmholtz (KH) instability at the interface between two superfluids – one rotating and anisotropic, the other stationary and isotropic – may trigger sudden spin-up of the stationary superfluid. This result suggests that a KH instability at the crust–core ( 1 S0 –3 P2 –superfluid) boundary of a neutron star may provide a trigger mechanism for pulsar glitches. We calculate the dispersion relation of the KH instability involving two different superfluids including the normal fluid components and their effects on stability, particularly entropy transport. We show that an entropy difference between the core and crust superfluids reduces the threshold differential shear velocity and threshold crust–core density ratio. We evaluate the wavelength of maximum growth of the instability for neutron star parameters and find the resultant circulation transfer to be within the range observed in pulsar glitches. 相似文献
19.
There is a 3P2 neutron superfluid region in NS (neutron star) interior. For a rotating NS the 3P2 superfluid region is like a system of rotating magnetic dipoles. It will give out electromagnetic radiation, which may provide a new heating mechanism of NSs. This mechanism plus some cooling agent may give a sound explanation to NS glitches. 相似文献
20.
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