强磁场中的逆Compton散射与γ射线爆能谱

本文认为强磁场中的逆Compton散射可能是γ射线爆的主要辐射机制.其能谱是由源区质子产生的低频光子经强磁场中非热电子的Compton散射形成的.我们利用非相对论情形(B/B_(cr)≤1,hv_i/m_ec~2≤1)下强磁场中的Compton散射微分截面,导出了上述Compton散射的辐射谱公式,由此很好地拟合了典型γ射线爆GB811016的观测能谱.     

中子星内部物理学——Ⅰ.整体性质和壳层物理

本文简单介绍了中子星整体概况、研究中子星外壳和内壳物理状况所用的方法和研究概况,最后简短介绍了强磁场对中子星表层物质性质的影响方面最重要的结论。     

强磁场对中子星壳层热核反应的影响

本文通过考虑强磁场中电子的量子效应，分析了强磁场下电子气体的Fermi能，讨论了磁场对核的屏蔽势和核反应率的影响，进而计算了强磁场对天体物理中几个较重要的热核反应的影响，结果表明，相对于无磁场而言，在较低密度下，足够强的磁场使原子核的屏蔽势显著增加，但在ρ／μe＞10~5molcm~(-3)的密度下，中子星表面存在的强度为10~5～10~9T范围内的磁场对核反应率几乎没有影响。     

强磁场中氢原子和氢分子离子的研究近况

已经确认中子星表面存在强磁场,所以强磁场中原子、分子(特别是H和H_2~ )的能级就成为颇具有吸引力的天体物理研究课题。 本文首先较详细地介绍了在强磁场中氢原子的薛定谔方程的几种近似解法,并对一些低能态的能量和波函数现已取得的较为满意的结果作了介绍。然后,综述了在同样条件下对H_2~ 的研究情况。最后,谈及这种问题中的相对论效应。     

超强磁场下的相对论电子

在以前工作的基础上,推导出超强磁场下简并的、相对论的电子压强P e的普遍表达式;讨论了电子的朗道能级量子化;探索了量子电动力学效应(QED)对中子压强占主导的理想的n-p-e气体系统的影响。主要结论包括:P e与磁场强度B、物质密度ρ及电子丰度Y e有关;磁场越强,电子压强越大;增加的压强是由高值的电子费米能引起的;在超强磁场下,磁星内部总压强是各向异性的;如果考虑到各向异性的总压强,磁星可能是一种更致密、形变后类似于椭球状的中子星;如果考虑到磁场能对状态方程的正能量的贡献,相对于普通射电脉冲星,磁星的质量可能更大些。     

强磁化等离子体中的多次康普顿散射

为了提供解开γ爆光谱之谜所需的信息,我们求解了γ光子在强磁化、纯散射等离子体中的输运问题。主要讨论了多次散射对湮灭线光子和γ射线连续谱的影响。计算中假定散射层由温度为10~7—10~8K的非简并等离子体组成,且带有B=4.414×10~(12)G的强磁场。使用了强磁场中的精确Compton散射截面。计算结果所显示的强磁场效应将有助于我们对γ爆光谱的更深入的认识。     

强磁场和γ爆的研究进展

本文首先对甚强磁场(B～10~(12)—10~(13)G)的物理研究现状进行了概要的评述,着重说明它在γ爆理论中的重要意义,指出辐射与强磁化等离子体的相互作用性质是目前最迫切的研究课题。在第二部分中,我们概述了宇宙γ射线爆的基本特征,以及目前对它的理论认识和尚未解决的理论问题,指出强磁场效应可能对γ爆特性具有深刻的影响。最后,我们简单描述了有关γ爆研究的最新进展,并由此展望了γ爆研究的方向。     

强磁场下逆康普顿散射的偏振特性

本文在Herold和我们前一工作的基础上,讨论了强磁场中不同情况(相对论情况和非相对论情况)下的逆Compton散射的偏振特性,并与无磁场情况进行了比较,得出一些有益的结果。在研究气体,尤其是具有强磁场天体的高能X射线和γ射线,甚至光学辐射机制时,这些偏振特性必须给予充分注意。     

状态方程与激波能量损失对Ⅱ型超新星爆发的影响

本文考察了实际的状态方程和激波能损对大质量星星核的绝热引力坍缩过程与结果的影响。结果表明,状态方程起着相当重要的作用,不同的状态方程给出很不相同的反弹时的中心密度ρ_(max)和反弹振幅。在不考虑激波能损时,本文所用的方程均给出爆发的结果;但考虑了激波能损,小振幅反弹就不能爆发了。     

强磁场对中子星壳层热核反应的影响

本通过考虑强磁场中电子的量子效应，分析了强磁下电子气体的Ｆｅｒｍｉ能，讨论了磁场对核的屏蔽势和核反应率的影响，进而计算了强磁场对天体物理中几个较重要的热核反应的影响。结果表明，相对于无磁场而言，在较低密度下，足够强的磁场使原子核的屏蔽势显增加，但在ρ／μｅ〉１０＾５ｍｏｌ．ｃｍ＾－３的密度下，中子星表面存在的强度为１０＾５～１０＾９Ｔ范围内的磁场对核反应率几乎没有影响。     

The evolution of the core and surface magnetic fields in isolated neutron stars

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.     

Vortex lines in neutron star superfluids and decay of pulsar magnetic fields

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.     

Natural MHD oscillations of a neutron star

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.     

Heat blanketing envelopes and thermal radiation of strongly magnetized neutron stars

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.     

Magnetic Neutron Stars. I. Static Field Configurations

The paper is the first in a series dealing with the structure of magnetic and rotating neutron stars including general relativistic effects. The geometry of fossile magnetic fields frozen in the highly conductive neutron star matter in a non-rotating (or weakly rotating) star is studied. § 2 treats the general poloidal field in a vacuum outside the star. The geometry of magnetic fields within the star — whose matter is governed by a barytropic equation of state — is restricted by the condition that the magnetic force density should be curl-free to maintain equilibrium (§ 3). Numerical results are obtained for a poloidal and a toroidal dipole field (§ 4).     

Linear Wave Beams in the Crust of a Neutron Star

The propagation of axially symmetric wave beams near the equatorial plane of a neutron star is studied. These waves are excited by a spatially bounded perturbation in the form of a transverse magnetic field applied to the inner boundary of the crust of the star. For a small ratio of the perturbed to the unperturbed magnetic field, a linear theory can be employed to solve the evolution equation. This condition is satisfied in the crust plasma of a neutron star for typical radio luminosities of pulsars. The resulting simple, exact solution in the form of linear gaussian beams exists without additional conditions on the dissipation, dispersion, and narrowness of the beams, if the velocity c _n of these waves is constant. The latter requirement is well satisfied for the plasma in neutron star crusts. The width of the gaussian beam also depends weakly on position.     

High frequency oscillations during magnetar flares

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.      

Evolution of neutron star magnetic fields

During the evolution of the neutron star its magnetic field first decays exponentially with the time and then may becomes quasi-stationary. The non-decaying magnetic field of the neutron star is generated by a degenerate electron gas which is in the Landau orbital ferromagnetism (LOFER) state. Possibly, due to the neutron star transition into the LOFER state, magnetic fields remained sufficiently strong in the case of such old magnetic neutron stars as powerful X-ray sources (e.g., Her X-1), millisecond pulsars and the binary pulsar PSR 0655+64.     

Impact of small bodies on to discs around compact objects — II. Interaction with the disc

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.     

Heating and cooling of magnetars with accreted envelopes

We study the thermal structure and evolution of magnetars as cooling neutron stars with a phenomenological heat source in an internal layer. We focus on the effect of magnetized (   B ≳ 10¹⁴  G) non-accreted and accreted outermost envelopes composed of different elements, from iron to hydrogen or helium. We discuss a combined effect of thermal conduction and neutrino emission in the outer neutron star crust and calculate the cooling of magnetars with a dipole magnetic field for various locations of the heat layer, heat rates and magnetic field strengths. Combined effects of strong magnetic fields and light-element composition simplify the interpretation of magnetars in our model: these effects allow one to interpret observations assuming less extreme (therefore, more realistic) heating. Massive magnetars, with fast neutrino cooling in their cores, can have higher thermal surface luminosity.