A Study of Neutron Star Structure in Strong Magnetic Fields that includes Anomalous Magnetic Moments

We study the effect of strong magnetic fields on the structure of neutronstar. We find that if the interior field is on the same order as the surface field currently observed, then the influences of the field on the star‘s mass and radius arenegligible; if the field is as large as that estimated from the scalar virial theorem,then considerable effects will be induced. The maximum mass of the star will be increased substantially while the central density is greatly reduced. The radius of a magnetic star can be larger by about 10%～20% than a nonmagnetic star of the same mass.     

Collective Spectra of Resonant Inverse Compton Scattering of Assembly of Relativistic Electrons in Intense Magnetic Fields*

The resonant inverse Compton scattering (RICS) of relativistic electrons in intense magnetic fields is an efficient mechanism for producing the highenergy γ-rays. In our previous work it is suggested that the early-stage γ-ray radiation of γ-ray bursts (GRBs) may be mainly produced by this mechanism. By using this mechanism, some puzzles in the study of GRBs can be clarified, e.g., the origin of the Amati relation obtained from the statistics of observations, the formation of the observed two-segment (broken) power-law spectra, the relevant “deadline problem”, the polarization property, etc. Herein our discussion will be focused on the formation of the broken power-law spectra. Based on the formula of the RICS spectral power of individual fast electrons, we have derived the simplified analytical formula of the collective RICS radiation spectrum (RICS spectral luminosity) produced by the assembly of relativistic electrons in an intense magnetic field when they pass through the ambient low-frequency radiation field, and applied it to several typical low-frequency radiation fields (e.g., the black-body radiation field, power-law radiation field and thermal bremsstrahlung field) around the central neutron star, for the convenience of comparison with the observed spectra. Our calculations indicate that the RICS radiation mechanism has a very high efficiency in the hard X-ray and γ-ray wavebands, if the matching condition (i.e., the condition approximate to resonance) is satisfied, and that independent of the ambient radiation field, the produced spectra are commonly the two-segment power-law spectra. Additionally, it is suggested that the RICS mechanism might be an ideal highly-efficient radiation mechanism for the high-energy emissions (hard X-rays and γ-rays) of the GRBs, soft γ-ray repeated bursts (SGRs) and γ-ray pulsars (GRPs).     

变化磁场中相对论电子系集体的共振逆康普顿散射谱

强磁场中的共振逆康普顿散射(RICS)是产生伽玛射线的有效机制．在前文工作的基础上，导出强磁场中子星中具有幂律能谱的大量相对论电子沿中子星磁轴向外运动时在变化磁场中产生的集体RICS辐射谱(RICS谱光度)的基本公式．由此得到在中子星周边几种典型的低频辐射场中集体RICS辐射谱形的简单解析表示(如热轫致辐射场、黑体辐射场，以及非热低频幂律谱辐射场)，以便与实际观测谱形比较．计算表明：在满足匹配条件(即近似共振条件)下，RICS辐射效率很高，其谱形都是两段式(折断的)的幂律谱形式，与周边低频场性质无关．通过计算，再一次论证RICS机制是伽玛射线脉冲星和伽玛暴(GRBs)在高能射线段(硬X-射线和伽玛射线)辐射的一个理想的高效辐射机制。     

Effects of Magnetic Fields on Neutrino-dominated Accretion Model for Gamma-ray Bursts

Many models of gamma-ray bursts suggest a common central engine:a black hole of several solar masses accreting matter from a disk at an accretion rate from 0.01 to 10 M_⊙s~(-1),the inner region of the disk is cooled by neutrino emission and large amounts of its binding energy are liberated,which could trigger the fireball.We improve the neutrino- dominated accreting flows by including the effects of magnetic fields.We find that more than half of the liberated energy can be extracted directly by the large-scale magnetic fields in the disk,and it turns out that the temperature of the disk is a bit lower than the neutrino-dominated accreting flows without magnetic field.Therefore,the outflows are magnetically-dominated rather than neutrino dominated.In our model,the neutrino mechanism can fuel some GRBs (not the brightest ones),but cannot fuel X-ray flares.The magnetic processes(both BZ and electromagnetic luminosity from a disk)are viable mechanisms for most of GRBs and their following X-ray flares.     

Milestones in the Observations of Cosmic Magnetic Fields

Magnetic fields are observed everywhere in the universe. In this review, we concentrate on the observational aspects of the magnetic fields of Galactic and extragalactic objects. Readers can follow the milestones in the observations of cosmic magnetic fields obtained from the most important tracers of magnetic fields, namely, the star-light polarization, the Zeeman effect, the rotation measures (RMs, hereafter) of extragalactic radio sources, the pulsar RMs, radio polarization observations, as well as the newly implemented sub-mm and mm polarization capabilities. The magnetic field of the Galaxy was first discovered in 1949 by optical polarization observations. The local magnetic fields within one or two kpc have been well delineated by starlight polarization data. The polarization observations of diffuse Galactic radio background emission in 1962 confirmed unequivocally the existence of a Galactic magnetic field. The bulk of the present information about the magnetic fields in the Galaxy comes from anal     

Magnetic field evolution in neutron stars

Neutron stars contain persistent, ordered magnetic fields that are the strongest known in the Universe. However, their magnetic fluxes are similar to those in magnetic A and B stars and white dwarfs, suggesting that flux conservation during gravitational collapse may play an important role in establishing the field, although it might also be modified substantially by early convection, differential rotation, and magnetic instabilities. The equilibrium field configuration, established within hours (at most) of the formation of the star, is likely to be roughly axisymmetric, involving both poloidal and toroidal components. The stable stratification of the neutron star matter (due to its radial composition gradient) probably plays a crucial role in holding this magnetic structure inside the star. The field can evolve on long time scales by processes that overcome the stable stratification, such as weak interactions changing the relative abundances and ambipolar diffusion of charged particles with respect to neutrons. These processes become more effective for stronger magnetic fields, thus naturally explaining the magnetic energy dissipation expected in magnetars, at the same time as the longer-lived, weaker fields in classical and millisecond pulsars. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magnetic fields in axisymmetric neutron stars

We derive general equations for axisymmetric Newtonian magnetohydrodynamics and use these as the basis of a code for calculating equilibrium configurations of rotating magnetized neutron stars in a stationary state. We investigate the field configurations that result from our formalism, which include purely poloidal, purely toroidal and mixed fields. For the mixed-field formalism, the toroidal component appears to be bounded at less than 7 per cent. We calculate distortions induced both by magnetic fields and by rotation. From our non-linear work, we are able to look at the realm of validity of perturbative work: we find for our results that perturbative-regime formulae for magnetic distortions agree to within 10 per cent of the non-linear results if the ellipticity is less than 0.15 or the average field strength is less than 10¹⁷ G. We also consider how magnetized equilibrium structures vary for different polytropic indices.     

Saa有挠引力模型下慢旋转磁中子星的电磁场

导出在Saa有挠引力模型下慢旋转磁中子星电磁场所满足的方程，并研究其外部解，得出如下结论：其一，选规范．A^0=0，电磁场存在某种形式的特解；其二，选规范A^0≠0，电磁场根本不存在此特解．故可通过观测中子星外部电磁场的形式判断挠率是否存在．     

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.     

Magnetic fields and rotation in white dwarfs and neutron stars

Recent spectropolarimetric observations of Ap and Bp stars with improved sensitivity have suggested that most Ap and Bp stars are magnetic with dipolar fields of at least a few hundred gauss. These new estimates suggest that the range of magnetic fluxes found for the majority of magnetic white dwarfs is similar to that of main-sequence Ap–Bp stars, thus strengthening the empirical evidence for an evolutionary link between magnetism on the main sequence and magnetism in white dwarfs. We draw parallels between the magnetic white dwarfs and the magnetic neutron stars and argue that the observed range of magnetic fields in isolated neutron stars  ( B_p ∼ 10¹¹–10¹⁵ G)  could also be explained if their mainly O-type progenitors have effective dipolar fields in the range of a few gauss to a few kilogauss, assuming approximate magnetic flux conservation with the upper limit being consistent with the recent measurement of a field of   B_p ∼ 1100 G  for θ Orion C.
In the magnetic field–rotation diagram, the magnetic white dwarfs can be divided into three groups of different origin: a significant group of strongly magnetized slow rotators  ( P _rot∼ 50 –100 yr)  that have originated from single-star evolution, a group of strongly magnetized fast rotators  ( P _rot∼ 700 s)  , typified by EUVE J0317–853, that have originated from a merger, and a group of modest rotators ( P _rot∼ hours–days) of mixed origin (single-star and CV-type binary evolution). We propose that the neutron stars may similarly divide into distinct classes at birth , and suggest that the magnetars may be the counterparts of the slowly rotating high-field magnetic white dwarfs.     

Soft gamma repeaters activity in time

In this short note I discuss the hypothesis that bursting activity of magnetars evolves in time analogously to the glitching activity of normal radio pulsars (i.e. sources are more active at smaller ages), and that the increase of the burst rate follows one of the laws established for glitching radio pulsars. If the activity of soft gamma repeaters decreases in time in the way similar to the evolution of core‐quake glitches (∝t^5/2), then it is more probable to find the youngest soft gamma repeaters, but the energy of giant flares from these sources should be smaller than observed 1044–1046 erg as the total energy stored in a magnetar's magnetic field is not enough to support thousands of bursts similar to the prototype 1979 March 5 flare. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The XMM‐Newton view of magnetars

Anomalous X‐ray Pulsars and Soft Gamma‐ray Repeaters are believed to be magnetars: isolated neutron stars powered by the decay of extremely high magnetic fields. We review some of the main results obtained with XMM‐Newton and discuss the prospects for future observations of this small but extremely interesting class of objects. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Coronal Flux Rope Equilibria in Closed Magnetic Fields

Using a 2.5-dimensional ideal MHD model in Cartesian coordinates,we investigate the equilibrium properties of coronal magnetic flux ropes in background magnetic fields that are completely closed.The background fields are produced by a dipole,a quadrupole,and an octapole,respectively,located below the photosphere at the same depth.A magnetic flux rope is then launched from below the photo-sphere,and its magnetic properties,i.e,the annular magnetic fluxφp and the axial magnetic fluxφz,are controlled by a single emergence parameter.The whole sys-tem eventually evolves into equilibrium,and the resultant flux rope is characterized by three geometrical parameters:the height of the rope axis,the half-width of the rope,and the length of the vertical current sheet below the rope.It is found that the geometrical parameters increase monotonically and continuously with increasing φp and φz:no catastrophe occurs.Moreover,there exists a steep segment in the profiles of the geometrical parameters versus either φp or φz,and the faster the background field decays with height,the larger both the gradient and the growth amplitude within the steep segment will be.     

中子星的热演化和磁衰减

本文研究了中子星的热演化、自转演化和磁场演化的相互影响．考虑了一个自洽模型：中子星因磁偶极辐射而自转减慢，在内部产生某些加热过程，中子星磁场通过壳层的欧姆耗散来衰减．结果表明，磁场衰减提高了加热过程的重要性；相反，加热效应减慢了磁衰减．因此可以得出，中子星的热、自转和磁场也许不是独立演化的．不仅如此，这些演化与初始条件有关，因此，人们也许可以从射电和Ｘ射线观测对脉冲星年龄、初始磁场和周期给出某些限制．     

Distribution of Helical Properties of Solar Magnetic Fields

We summarize studies of helical properties of solar magnetic fields such as current helicity and twist of magnetic fields in solar active regions (ARs), that are observational tracers of the alpha-effect in the solar convective zone (SCZ). Information on their spatial distribution is obtained by analysis of systematic mag-netographic observations of active regions taken at Huairou Solar Observing Station of National Astronomical Observatories of Chinese Academy of Sciences. The main property is that the tracers of the alpha-effect are antisymmetric about the solar equator. Identifying longitudinal migration of active regions with their individual rotation rates and taking into account the internal differential rotation law within the SCZ known from helioseismology, we deduce the distribution of the effect over depth. We have found evidence that the alpha-effect changes its value and sign near the bottom of the SCZ, and this is in accord with the theoretical studies and numerical simulations. We discuss     

强磁场中相对论电子系集体的共振逆康普顿散射谱

强磁场中相对论电子的共振逆康普顿散射(RICS)是产生伽玛射线的有效机制.以前的工作曾论证,伽玛暴(GRB)的早期伽玛射线辐射可能主要由该机制产生.利用此辐射机制,伽玛暴研究中的一些困惑有可能得到较好的解释.例如,观测统计给出的"Amati关系"的起源,两段式(折断式)幂律谱的形成,特别是其中"死线问题"的解决方案,还有偏振的存在等.这里将重点讨论折断幂律谱形成问题.基于单个电子的RICS谱功率公式,导出了强磁场中大量相对论电子穿过周边低频辐射场时产生的集体RICS辐射谱(RICS谱光度)的简化解析公式,并将它应用于中子星周边几种典型的低频场(如黑体辐射场、幂律辐射场以及热轫致辐射场),以便与实际观测谱形比较.计算表明:在满足匹配条件(即近似共振条件)下,RICS辐射效率很高,其谱形普遍为两段式的幂律谱形式,与周边低频场性质无关.还论证RICS机制可能是伽玛暴、软伽玛重复暴和伽玛射线脉冲星在高能射线波段(硬X射线和伽玛射线)的一个理想的高效辐射机制.