脉冲星的非共转模型

本文讨论了脉冲星的磁层运动和能量状态。对于满足一定条件的脉冲星系统,证明了在极轴处的等离子体的角速度和电荷密度趋于零。提出了一个磁层与星体非共转的简单模型以及边界条件。利用变分原理,求得参数值,从而,得出了与参数相关的各个物理量,例如:等离子体的漂移速度v_D,等离子体与星体的相对滑动速度v_s,脉冲星的输出功率等。结果表明:功率值比较接近观测值,非共转的模型相对通常采用的共转模型而言是比较合理的。     

中子星自洽的有限磁层大气模型

本文讨论的是中子星自洽的有限磁层大气模型,先用试探解方法得到一个解析解,它给出有限磁层大气的分布轮廓,然后用能量最小原理讨论了其特性,取得了有意义的结果。同时,通过对其等离子体与真空交界面的研究,得出其交界面也是稳定的。最后,我们对模型的发展作了展望,指出赤道区的超共转,可能与子脉冲漂移有关,从这个模型出发,我们将可能最终建立一个自洽的有辐射的模型。     

H(z)数据对相互作用暗能量模型的观测研究

结合最新的哈勃参量H(z)观测数据、重子声学振荡(BAO)数据与普朗克卫星观测得到的宇宙微波背景辐射(CMB)数据,利用马尔柯夫链蒙特卡洛算法(MCMC)对一种相互作用暗能量模型进行了观测限制.这3种数据联合限制得到的各参数的最佳拟合值及1σ误差范围分别为:物质能量密度参数?m=0.266+0.028-0.028,相互作用因子γ=0.090+0.100-0.098,暗能量状态方程参数wX=-1.307+0.263-0.269,哈勃常数H0=74.20+4.66-4.56.相互作用耦合参数γ0表明能量正在从暗物质转移到暗能量.然而,宇宙学常数模型中的巧合性问题在1σ误差范围内依然可以轻微缓解.为了更好地做出比较,还利用BAO+CMB组合数据及单独的H(z)数据对该模型进行了考察,得到的结果如下:(1)H(z)数据能对相互作用参数γ给出更好的限制结果;(2)ΛCDM模型仍然是与观测数据符合得最好的模型,耦合参数γ与其它模型参数(?m,H0)相互关联;(3)在考虑了暗能量与暗物质间的相互作用之后,超新星局域距离阶梯测量与普朗克观测对H0限制结果的冲突问题能够得到一定程度的缓解.     

超新星SN1987A包层的温度演化

本文介绍了超新星ＳＮ１９８７Ａ爆发六年来关于其包层温度演化的研究情况。温度是研究超新星的各种物理过程的一个基本参量，然而目前对温度的各种估算十分弥散，结果相当不确定。本文利用辐射转移理论的逃逸几率方法，导出Ｈａ线辐射理论光变曲线，通过与观测曲线的比较，可定量地导出超新气壳的温度演化行为。这一模型的结果与他人结果有较好的符合。同时，我们的结果表明，在爆发５００天以后，温度反而随年龄上升，可能的解释在     

恒星大气物理参量的非参数估计方法

恒星大气物理参量（有效温度、表面重力、化学丰度）是导致恒星光谱差异的主要因素．恒星大气物理参量的自动测量是LAMOST等大规模巡天望远镜所产生的海量天体光谱数据自动处理中一个重要研究内容．针对测量大样本的恒星光谱数据估计每个恒星的大气物理参量，提出了一种基于变窗宽核函数的估计算法：变窗宽算法是对固定窗宽算法的改进，分为3个步骤：（1）将历史恒星光谱数据进行PCA处理，得到光谱的低维特征数据；（2）利用特征数据与其物理参数的对应关系，建立一种变窗宽的非参数估计模型；（3）利用该估计模型，直接计算待测恒星光谱的3个物理参量（有效温度、表面重力、金属丰度）．实验结果表明：该方法与固定窗宽估计模型以及在其他文献中报道的方法相比，具有较高的估计精度和鲁棒性．     

大质量X射线双星脉冲星4U 1901+03的脉冲轮廓研究

大质量X射线双星脉冲星4U 1901 03在沉寂30多年后,于2003年1月爆发.利用罗西X射线时变探索者卫星RXTE为期5个月的观测数据,对其脉冲轮廓进行了系统研究,得到了该源的脉冲轮廓演化以及能量相关性,脉冲比例演化和脉冲比例对能量的依赖关系.研究发现,4U 1901 03的脉冲轮廓和脉冲比例随双星系统的吸积率变化呈现阶段性的演化,脉冲比例在十几keV处达到峰值.这些脉冲轮廓的复杂变化表明,脉冲轮廓不能用单一的几何或物理模型解释,而是与观测角度以及X射线源的辐射机制相关.利用标准的脉冲星辐射模型讨论了4U 1901 03脉冲轮廓的观测现象.     

矮新星AB Dra中的吸积盘模型

对矮新星ＡＢ Ｄｒａ的最小二乘拟合表明，黑体吸积盘模型预言的连续谱能粗略地拟合该星在爆发期间的ＩＵＥ观测，较小的偏差可以归因于光学薄气体的复合辐射或／和热斑的黑体辐射，拟合给出了一组吸积盘参量的合理值。     

太阳大气中矢量磁场信息的推导

一种能从观测到的斯托克斯轮廓中提取太阳表面矢量磁场信息的方法在本文中提出，它利用斯托克斯轮廓非线心的极值点处相应参量对波长的导数为零这一数学事实，假设表面附近磁场矢量及热力学参量的变化梯度足够小以致所考虑的极值点的波长位置不随深度改变或此变化呆忽则使得偏振辐射围方程组得到极大的简化；再应用数值方法从此简化方程组中解出辐射表面附近的磁场矢量参数。通过拟合理论轮廓表明该法确实可以得到表面近似的磁场矢量     

中子辐照量指数分布函数式中比例系数和平均中子辐照量的计算公式

已有的研究表明,在AGB(Asymptotic Giant Branch)星s-过程核合成模型发展演化的3个典型阶段中,其核合成区域中子辐照量分布在有效取值范围内都可视为指数分布,即ρ_(AGB)(τ)=C/τ_0 exp(-τ/τ_0),但式中比例系数C和平均中子辐照量τ_0的具体表达式相关文献中并未全部给定.通过深入剖析中子辐照量指数分布函数的基本求解方法,并系统梳理不同恒星模型中子辐照量分布函数的求解过程,得到了C和τ_0的计算通式及其辅助关系式.只要确定了恒星模型中子辐照量的分立分布函数,就可以据此组公式确定出C和τ_0与模型参量之间的关系式.所得结果有效地解决了利用解析方法求解目前流行的~(13)C壳层(~(13)C pocket)辐射燃烧AGB星s-过程核合成模型中子辐照量分布问题.     

电子回旋脉泽不稳定性驱动的太阳射电辐射机制

在解释天体爆发过程中的短时标相干射电辐射现象方面,非热电子驱动的回旋脉泽辐射得到了广泛应用.在以往的研究中,一个关键条件是非热电子具有各向异性速度分布,从而有效激发回旋脉泽不稳定性.然而,观测显示太阳和其他天体的非热电子经常呈现负幂律谱形式的能量分布.非热电子的这种负幂律能谱特征会严重抑制回旋脉泽不稳定性放大率,因此,进一步研究非热电子的负幂律能谱分布行为,能拓宽电子回旋脉泽辐射机制的适用性,很好地发展天体射电辐射机制理论.最近研究结果显示,负幂律谱电子的低能截止行为可以有效地激发电子回旋脉泽辐射,从而拓宽了其在天体物理研究中的应用范围.     

The energy loss of a rotating magnetized neutron star

The analysis of observations of pulsar B1931+24 shows that the mechanism of the spin-down of a rotating magnetized neutron star is due to the plasma generation in its magnetosphere and, consequently, the radio emission generation. The unique observation of the switch on and switch off of this pulsar allows us to distinguish between the energy loss in the absence of radio emission (the magnetodipole radiation) and the current loss due to the rotation energy expenditure to the relativistic plasma generation and acceleration in the pulsar magnetosphere. The inclination angle χ, the angle between the rotation axis and the magnetic dipole axis, can be stationary for this pulsar,  χ=χ_st  . From observations and theory it follows that  χ_st= 59°  .     

Coulomb-trapped particles in the electromagnetic fields of an oblique magnetic rotator

An oblique, rotating magnetized sphere emits electromagnetic waves which, for large magnetization, can quickly accelerate charged particles to very high energies. A central, attractive Coulomb force can trap particles in the region beyond the light cylinder by balancing the accelerating influence of the radiation on the particles. We sample some of the particle orbits possible under these dynamical conditions. A general feature of these orbits is that non-interacting particles started with random initial conditions in the domain of attraction of these orbits will arrange themselves on a curve corotating with the axis of magnetization. Such particle configurations can be a source of pulsed radiation. In the idealized case of no interparticle interactions the spectral index for the radiation emitted by one frequently occurring configuration is found to be –2/3, for emission from radio to -ray frequencies. The dynamical conditions in this simple model closely match those prevalent in outer pulsar magnetospheres, making it possible that part of the radiation from pulsars is emitted by trapped plasma in the region beyond the light cylinder.     

Nature of the soft x-ray excess in the spectrum of RX J1037.5-5647

The source responsible for the soft x-ray excess in the emission spectrum of the pulsar RX J1037.5-5647 is associated with a hot spot on the surface of the neutron star near the base of an accretion column. The intensity of the emission from this source, however, only undergoes small (on the order of 15%) variations, while the intensity of the hard component varies substantially with the rotation period of the neutron star. We show that this situation can occur if the angle between the axis of rotation and the magnetic axis of the neutron star is no more than 8°. The variation in the intensity of the hard component of the radiation in this case is interpreted in terms of an anisotropy in the directional diagram. In this scenario, the angle of inclination of the orbit of the binary system is close to 10°.     

Spectral Constraints for Millisecond Pulsars Due to General Relativistic Frame Dragging

We develop a numerical code for simulating the magnetospheres of millisecond pulsars, which are expected to have unscreened electric potentials due to the lack of magnetic pair production. We incorporate General Relativistic (GR) expressions for the electric field and charge density and include curvature radiation (CR) due to primary electrons accelerated above the stellar surface, whereas inverse Compton scattering (ICS) of thermal X-ray photons by these electrons are neglected as a second-order effect. We apply the model to PSR J0437-4715, a prime candidate for testing the GR-Electrodynamic theory, and find that the curvature radiation spectrum cuts off at energies below 15 GeV, which are well below the threshold of the H.E.S.S. telescope, whereas Classical Electrodynamics predict a much higher cutoff near 100 GeV, which should be visible for H.E.S.S., if standard assumed Classical Electrodynamics apply. GR theory also predicts a relatively narrow pulse (2φ _L ∼ 0.2 phase width) centered on the magnetic axis, which sets the beaming solid angle to ∼0.5 sr per polar cap (PC) for a magnetic inclination angle of 35^∘ relative to the spin axis, given an observer which sweeps close to the magnetic axis. We also find that EGRET observations above 100 MeV of this pulsar constrain the polar magnetic field strength to B _pc < 4× 10⁸ G for a pulsar radius of 10 km and moment of inertia of 10⁴⁵ g cm². The field strength constraint becomes even tighter for a larger radius and moment of inertia. Furthermore, a reanalysis of the full EGRET data set of this pulsar, assuming the predicted pulse shape and position, should lead to even tighter constraints on neutron star and GR parameters, up to the point where the GR-derived potential and polar cap current may be questioned.     

On the theory of X-ray pulsar radiation

The origin of hard X-ray spectrum (continuum and cyclotron lines) of pulsars in binary systems is discussed. A model of the polar region of a neutron star consisting of a hot spot in a dense plasma atmosphere with a quasi-homogeneous magnetic field and an extended accreting column in an inhomogeneous dipolar field is investigated. In the hot spot bremsstrahlung and Thomson scattering form continuum radiation, while bremsstrahlung and cyclotron scattering produce the absorption cyclotron lines. By the observed continuum intensity one can estimate the maximum distances to pulsars. Cyclotron scattering in gyro-resonant layers localized in the accreting column leads to a general attenuation of the radiation of a hot spot, but is unable to ensure the formation of cyclotron lines. For strong accretion the hot spot radiation becomes insignificant, the lines disappear and the pulsating component of an X-ray pulsar is produced by the accreting column bremsstrahlung transformed by Thomson scattering.     

Mapping the magnetosphere of PSR B1055−52

We present a geometric study of the radio and γ-ray pulsar B1055−52 based on recent observations at the Parkes radio telescope. We conclude that the pulsar's magnetic axis is inclined at an angle of 75° to its rotation axis and that both its radio main pulse and interpulse are emitted at the same height above their respective poles. This height is unlikely to be higher or much lower than 700 km, a typical value for radio pulsars.
It is argued that the radio interpulse arises from emission formed on open fieldlines close to the magnetic axis which do not pass through the magnetosphere's null (zero-charge) surface. However, the main pulse emission must originate from fieldlines lying well outside the polar cap boundary beyond the null surface, and farther away from the magnetic axis than those of the outer gap region where the single γ-ray peak is generated. This casts doubt on the common assumption that all pulsars have closed, quiescent, corotating regions stretching to the light cylinder.     

Force-free pulsar magnetospheres

The equations to the steady, axisymmetric, charged pulsar magnetosphere given recently by Michel (1973a, b) and Scharlemann and Wagoner (1972, preprint) are generalized to non-axisymmetric systems that are steady in the frame rotating with the pulsar. It is shown that in all nonsingular models with cylindrical (but not axial) symmetry, and with a non-zero magnetic field component parallel to the axis, the magnetic field lines emanating from the pulsar are all trapped within the light-cylinder, so that there is no net electromagnetic energy flow across the light cylinder.     

脉冲星射电轮廓中高斯成分在主脉冲和中间脉冲的不同分布

研究了高斯辐射成分在可视点所画出轨迹上的分布,这个可视点因脉冲星的转动而作非匀速度运动.通过假设辐射区域围绕磁轴均匀分布,一个高斯辐射成分便对应于可视轨迹划过的一个辐射区域.因为演示辐射区域在可视轨迹上是不均匀的分布,因此高斯成分沿轨迹也是不均匀的,而高斯成分的密度在磁轴与视线距离最近时为最大.高斯成分的分布取决于脉冲星的两个角度:旋转轴和视线之间的夹角,以及磁轴和旋转轴之间的倾角.基于此模型,一个脉冲星平均轮廓中观察到的多个高斯成分便对应于可视轨迹在特定的转动相位范围内的辐射区域.演示了脉冲星旋转的近侧和远侧的相位,分别对应的主脉冲和中间脉冲,两者高斯成分的数量和分布是不同的.而且还发现,沿可视轨迹上的辐射区域总数与围绕磁轴的辐射区域的总数是不同,并且预测的辐射区域数目会因忽略可见点的运动而明显不同.拟合表明脉冲星轮廓的高斯成分的形状和数量可能与实际构成轮廓的成分的形状和数量不同.以PSR B0826–34的辐射为例,并假设辐射来自单一磁极.     

On the formation of pulsar radiation diagrmas

A model of pulsars is discussed in which formation of a polar diagram of the radiation is influenced by the motion of the source around a neutron star with a velocity close to that of light. For a power-law frequency-spectrum of the radiation and isotropy of the diagram in a system of coordinates rotating with the source, the width of the observed pulse is shown to be independent of frequency.The proposed explanation of the second period characteristics of type CP 1919 pulsars is based on the effect of relativistic motion of the radiation source. The positions are established (relative to the axis of rotation of the star) of the local sources of radiation in the optical and in the radio ranges for the pulsar NP 0532. It is shown how the polarization characteristics of the optical radiation of this pulsar may be connected with the effects of relativistic orbiting of the source of radiation about the star.     

Energetics of galactic nuclei

A model of compact galactic nuclei in statistical equilibrium was developed in [L. Sh. Grigorian and G. S. Sahakian, Astrofizika (in press)]. It was shown that they should consist predominantly of neutron stars (pulsars) and white dwarfs. The problem of the energy reserves of galactic nuclei is discussed in terms of this concept. The mechanism of conversion of a white dwarf into a neutron star due to the accretion of interstellar matter is considered. This means that a galactic nucleus has an energy reserve of some 5·10⁶⁰ N₈ erg (N is the number of stars in the nucleus). It is shown that galactic nuclei are powerful sources of hard γ radiation [power L » 2·10⁴⁴µ₃₀N₈(Ω/50)^17/7 erg/sec, where µ is the magnetic moment and Ω is the angular rotation rate of a neutron star ] due to curvature radiation from relativistic electron fluxes flowing along channels of open magnetic field lines of pulsars. The x-ray and ultraviolet emission are due to synchrotron emission from the same electron fluxes in the magnetic field of the galactic nucleus (L » 10⁴²-10⁴⁴ erg/sec). The optical (visible and infrared) and radio emission are due to bremsstrahlung from electrons in the interstellar medium [L » 6·10⁴⁶N ₈ ² (5/R_pc)³ erg/sec, where R is the radius of the galactic nucleus]. An equation is obtained for the magnetic moment of a pulsar: µ ≈ 3.4·10^-5L_γP^17/7, where P is the pulsar’s period and L_03B3; is the luminosity of the pulsar’s y radiation.