从光速圆柱磁能的衰减研究毫秒脉冲双星的演化

本文用脉冲星光速圆柱附近磁能的衰减理论研究了毫秒脉冲星的演化。文中从理论了给出了脉冲星到达辐截止线时的年龄和自转周期，及现在的辐射年龄和从现在辐射年龄到达辐截止线所需的时间。并用此理论对７颗脉冲双星的演化作了数值计算。     

脉冲星的一种分类方法及辐射部位的统计研究

本文对83颗脉冲星进行了分类统计研究。主要结果如下: 1.采用转动能损失率与射电光度的比值作为分类参数可以较好地反映不同类型脉冲星的物理特性和演化方式。 2.由于各类脉冲星的射电光度和光速圆柱附近的磁能之间都有着相关系数较高的回归关系,而射电光度和表面磁能之间却不相关,由此推论脉冲星辐射部位很可能在光速圆柱附近。 3.在周期变率户和周期P的关系图上,光速圆柱附近的“缠绕”磁能PP-4的某一临界值可作为射电辐射的截止线,它比Lyne等提出的光速圆柱处的磁能户PP~(-5)作为射电辐射截止线更接近观测事实。     

脉冲星的辐射特征和空间分布的统计分析

本文采用330颗脉冲星星表,进一步论讨了脉冲星某些重要特性的演化规律,主要结果如下:1.脉冲星的转动能损率E,射电光度L_R,磁能和辐射锥角都随年龄的增加而迅速减少。这表明,脉冲星的能量和辐射都是逐渐衰减的;2.射电转换效率η_R随年龄的增加而增加,这可能表明脉冲星辐射频谱的极大值逐渐向射电波段演化;3.脉冲星离银道面的距离|z|随年龄的增加而增加,这意味着多数脉冲星可能都是离银道面而去的。     

缺脉冲现象显著的脉冲星的若干特性

本文把呈现缺脉冲现象的脉冲星作为一种次型来进行研究。发现缺脉冲现象显著的脉冲星分布在射电辐射的截止线附近,组成一条近于和截止线平行的直线。此外,这种脉冲星还有如下的特点:它在光速圆柱距离处的磁场偏小,能损率也偏小。文中讨论了缺脉冲产生的可能原因。     

脉冲星缺脉冲现象的统计分析

本文对呈现缺脉冲现象的脉冲星进行了统计分析，发现缺脉冲百分率ＮＦ与脉冲等值宽度Ｗｅ有更显著的相关关系，即比Ｂｉｇｇｓ得到的ＮＦ－Ｐ和ＮＦ－α关系相关程度更高，利用Ｆｉｌｉｐｐｅｎｋｏ和Ｒａｄｈａｋｒｉｓｈｎａｎ模型，本文推导出ＮＦ的近似表达式，解释了上述统计结果。虽然缺脉冲现象总体上与年龄相关不大，即年龄大不是出现缺脉冲的必要条件，但缺脉冲现象显著的脉冲星确实分布在射电辐射的截止线附近，组成了一条和截止线近似平行的直线，反映了这类脉冲星的确处于老年阶段。本文对产生缺脉冲的原因作了简要的讨论。     

脉冲星参数空间分布和演化统计研究

脉冲星参数统计是脉冲星研究的重要基础性工作。利用最新整理的脉冲星观测数据,对2 500多颗脉冲星参数的空间分布和演化进行了统计研究。结果显示,在空间上脉冲星集中在银道面附近,脉冲星数目分布的极大值位于距离银心约7.27 kpc处,这可能是星际色散和散射造成的观测效应。另外给出了自转周期、表面磁场、特征年龄和自转能损失率随着远离银道面的变化规律。随着远离银道面,常规脉冲星的自转周期和特征年龄不断增大,表面磁场和自转能损失率不断减小。常规脉冲星的射电光度随特征年龄的增大,先增大后减小,这表明射电辐射机制在不同年龄段有所不同。常规脉冲星自转能损失率随特征年龄的增大呈对数快速下降。这些结果是脉冲星分布演化理论研究的重要基础。     

脉冲星减速研究与电磁和引力波辐射

脉冲星具有极强的磁场,由于其磁轴与自转轴并不完全重合,这使脉冲星存在电磁辐射.脉冲星靠消耗自转能来弥补辐射出去的能量,从而导致自旋速度的逐渐放慢.根据理论推导,对蟹状星云脉冲星(Crab)的初始周期进行预测,并推导出在未来任意时刻,在电磁辐射的影响下,其脉冲星自旋周期的演化规律.由于脉冲星的质量分布可能存在四极矩,引力波辐射也会使得脉冲星的旋转速度减小,因此进一步分析Crab脉冲星在引力波影响下自旋周期的变化.最后将两种辐射机制模型结合,对脉冲星在两种辐射机制共同作用下自旋周期的演化进行分析.     

脉冲星观测研究的某些进展

近年来,对日益增加的脉冲星观测资料的分析和对毫秒脉冲星、射电和X射线脉冲双星的观测,对脉冲星的形成、演化和辐射机制等提出了越来越多的新问题。本文对这些新问题的观测依据进行了介绍。主要涉及下述几方面的问题:是否存在着在结构、形成和演化上均不相同的两类脉冲星?脉冲星是否有两种或两种以上的辐射机制在同时起作用?脉冲星射电辐射中的两种相互垂直的偏振模式,以及近年来在毫秒脉冲星、射电和X射线脉冲双星的观测中所发现的新现象等。     

毫秒脉冲星

毫秒脉冲星PSR1937 214的发现是近几年天体物理学中的一次重要事件。本文介绍了该星的发现史和主要观测事实。该星自转周期为1.557806449023毫秒,是转动最快的脉冲星。周期变率为1.24×10~(-19)秒/秒。在它的周围没有明亮的超新星遗迹。这颗脉冲星的引人注目的特征是磁场低和在P—P图上位置独特。文中还评述了解释这颗脉冲星的四种模型;(1)起源于吸积X射线双星的中子星,通过从伴星吸积物质而加速到毫秒周期;(2)Michel和Dessler提出的盘模型脉冲星中的普通一员;(3)双中子星并合体;(4)辐射年龄小的脉冲星。最后一种可能性是本文作者提出的。根据具有相似特征的脉冲星倾向于分布在同一条PP~(-5)等值线及可按等值线排成演化序列的事实,作者按光速圆柱磁能衰减来定义脉冲星辐射年龄t:B/8π∝PP~(-5)=C_0exp(-2t/τ)(τ为磁能衰减时标),井据此认为PSR1937 214和蟹状星云脉冲星、船帆座脉冲星都是辐射年轻的。     

脉冲星磁场的演化

综述了前人对于单个脉冲星磁场的起源和演化的研究结果及其最新进展。脉冲星磁场的起源有多种模型，其所对应的初始磁场有两种位形：磁场束缚在核内和磁场束缚在壳层中。脉冲星的磁场如何演化，没有一致的结论。有各种观测证据可能直接或间接表明磁场的演化行为，如根据特征年龄和运动学年龄的差异可以推断出脉冲星磁场按指数规律衰减，而根据特征年龄与超新星遗迹年龄的差异或几颗年轻脉冲星的制动指数可以认为年轻脉冲星的磁场可能是增强的。脉冲星的样本合成研究（数值模拟）是研究脉冲星磁场演化的重要方法。模拟结果表明，假定脉冲星磁场按指数衰减，特征衰减时标必须为10^7yr或更长。而壳层中磁场的欧姆耗散模型数值计算显示脉冲星磁场演化行为因冷却模型和状态方程的取法不同而异，但最终无明显的衰减。由自转变慢诱导的脉冲星核内部磁场向壳层中扩散模型的计算表明脉冲星磁场的衰减只发生在10^7-10^8yr这段时间内，磁场衰减1－2个量级。     

Studying millisecond pulsars in X-rays

Millisecond pulsars represent an evolutionarily distinct group among rotation-powered pulsars. Outside the radio band, the soft X-ray range (～0.1–10 keV) is most suitable for studying radiative mechanisms operating in these fascinating objects. X-ray observations revealed diverse properties of emission from millisecond pulsars. For the most of them, the bulk of radiation is of a thermal origin, emitted from small spots (polar caps) on the neutron star surface heated by relativistic particles produced in pulsar acceleration zones. On the other hand, a few other very fast rotating pulsars exhibit almost pure nonthermal emission generated, most probably, in pulsar magnetospheres. There are also examples of nonthermal emission detected from X-ray nebulae powered by millisecond pulsars, as well as from pulsar winds shocked in binary systems with millisecond pulsars as companions. These and other most important results obtained from X-ray observations of millisecond pulsars are reviewed in this paper, as well as results from the search for millisecond pulsations in X-ray flux of the radio-quite neutron star RX J1856.5-3754.     

Statistical Analysis of Physical Parameters of Pulsars

Thanks to the excellent performance of FAST (Five-hundred-meter Aperture Spherical radio Telescope), the number of pulsars has increased rapidly. It is very important to analyze the physical parameters of known pulsars. The overall properties of pulsars are studied by analyzing the related physical parameters such as spatial position, period, surface magnetic flux density and so on. A large number of pulsars were detected by FAST near the galactic disk, which reflect the superiority of its detection ability. The diagram of the relationship between the period and the time derivative of period of pulsars has been updated. At present, 57 pulsars have crossed the classical “death line”, and five were discovered by FAST. Finally, the physical parameters of the binary pulsar systems are statistically analyzed, the binary pulsar systems are evolving towards the direction of low eccentricity and the decrease mass of the companion star. Moreover, 9 are located above the “spin-up line”. FAST is making China into the golden age of pulsar discovery, which will further promote the rapid development of pulsar physics.     

脉冲星参数统计和演化

统计分析了目前发现的几种脉冲星的自转周期和表面磁场以及空间的分布情况,揭示出毫秒脉冲星比普通射电脉冲星、LMXB(低质量X射线双星)比HMXB(高质量X射线双星)的空间分布要更加弥散;孤立毫秒脉冲星自转周期分布的峰值为4.7 ms,而普通脉冲星的相应值为0.6 s,双星中毫秒脉冲星这一值为3.5 ms; FERMI脉冲...     

Some characteristics of pulsars with long pulse nulling

Taking pulsars with long pulse nulling as forming a special group, we found that those with pronounced nulling are located on a line near and parallel to the radio cut-off in the 1gP — 1gP diagram. This in turn suggests a reason for the nulling. They are also shown to have smaller than average fields at the light cylinder and to have smaller than average rates of energy dissipation.     

Radio-Loud and Radio-Quiet Gamma-Ray Pulsars from the Galaxy and the Gould Belt

We present results of a population synthesis study of radio-loud and radio-quiet γ-ray pulsars from the Galactic plane and the Gould Belt. The simulation includes the Parkes multibeam pulsar survey, realistic beam geometries for radio and γ-ray emission from neutron stars and the new electron density model of Cordes and Lazio. Normalizing to the number of radio pulsars observed by a set of nine radio surveys, the simulation suggests a neutron star birth rate of 1.4 neutron stars per century in the Galactic plane. In addition, the simulation predicts 19 radio-loud and 7 radio-quiet γ-ray pulsars from the plane that EGRET should have observed as point sources. Assuming that during the last 5 Myr the Gould Belt produced 100 neutron stars, only 10 of these would be observed as radio pulsars with three radio-loud and four radio-quiet γ-ray pulsars observed by EGRET. These results are in general agreement with the recent number of about 25 EGRET error boxes that contain Parkes radio pulsars. Since the Gould Belt pulsars are relatively close by, the selection of EGRET radio-quiet γ-ray pulsars strongly favors large impact angles, β, in the viewing geometry where the off-beam emission from curvature radiation provides the γ-ray flux. Therefore, the simulated EGRET radio-quiet γ-ray pulsars, being young and nearby, most closely reflect the current shape of the Gould Belt suggesting that such sources may significantly contribute to the EGRET unidentified γ-ray sources correlated with the Gould Belt.     

Millisecond Pulsars,their Evolution and Applications

Millisecond pulsars (MSPs) are short-period pulsars that are distinguished from “normal” pulsars, not only by their short period, but also by their very small spin-down rates and high probability of being in a binary system. These properties are consistent with MSPs having a different evolutionary history to normal pulsars, viz., neutron-star formation in an evolving binary system and spin-up due to accretion from the binary companion. Their very stable periods make MSPs nearly ideal probes of a wide variety of astrophysical phenomena. For example, they have been used to detect planets around pulsars, to test the accuracy of gravitational theories, to set limits on the low-frequency gravitational-wave background in the Universe, and to establish pulsar-based timescales that rival the best atomic-clock timescales in long-term stability. MSPs also provide a window into stellar and binary evolution, often suggesting exotic pathways to the observed systems. The X-ray accretion-powered MSPs, and especially those that transition between an accreting X-ray MSP and a non-accreting radio MSP, give important insight into the physics of accretion on to highly magnetized neutron stars.     

Radio pulsars with expected gamma radiation and gamma-ray pulsars as pulsating radio emitters

Pulsars play a crucial astrophy sical role as highly energetic compact radio, X-ray and gammaray sources. Our previous works show that radio pulsars identified as pulsing gamma-ray sources by the Large Area Telescope(LAT) on board the Fermi Gamma-Ray Space Telescope have high values of magnetic field near the light cylinder, two-three orders of magnitude stronger compared with the magnetic fields of radio pulsars: log B_(lc)(G) are 3.60-3.95 and 1.75 correspondingly. Moreover,their losses of rotational energy are also three orders higher than the corresponding values for the main group of radio pulsars on average: log E(erg s~(-1)) = 35.37-35.53 and 32.64. The correlation between gammaray luminosities and radio luminosities is found. It allows us to select those objects from all sets of known radio pulsars that can be detected as gamma-ray pulsars with high probability. We provide a list of such radio pulsars and propose to search for gamma emission from these objects. On the other hand,the known catalog of gamma-ray pulsars contains some sources which are not currently identified as radio pulsars. Some of them have large values of gamma-ray luminosities and according to the obtained correlation, we can expect marked radio emission from these objects. We give the list of such pulsars and expected flux densities to search for radiation at frequencies 1400 and 111 MHz.     

A search for soft X-ray radiation from pulsars with the Astronomical Netherlands Satellite

We present the results of a search for X-ray emission in the energy range 0.2–0.28 keV and 1–7 keV from a number of radio pulsars, including Crab, Vela and the binary pulsar PSR 1913+16, using the soft X-ray experiment aboard ANS. Except for the Crab no pulsed flux has been found. From the Vela pulsar we have detected continuous flux in agreement with earlier observations. Upper limits are given.Paper presented at the COSPAR Symposium on Fast Transients in X-and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.     

Interpretation of no radio pulsar inside supernova 1987A: The high plasma cut-off frequency by the remnant media

Three decades have passed since the supernova SN 1987A was observed in the Large Magellanic Cloud, inside which the product is most likely a neutron star (NS) formed in the core collapse explosion.Although lots of observations with sensitive radio telescopes have taken place, astronomers have not yet detected any evidence for a radio pulsar around the remnant of 1987A. To investigate pulsars inside the SN remnants, we calculate the cut-off oscillation frequency of the plasma around the presumed NS inside SN1987A, as shown to be about 33 GHz at present (2018 CE), which is much higher than the favorite “searching window” (e.g. L-band ∼ 1.4 GHz) of radio pulsar surveys that have been commonly exploited by astronomers. Since radio waves with frequencies lower than the plasma cut-off frequency cannot penetrate the SN remnant media, we suggest that astronomers use higher frequency bands to search for a pulsar in SN 1987A.Furthermore, with the expansion of SN remnant media, we find that the plasma cut-off frequency can decay to the L-band (1.4 GHz) in the future. The strategy of finding a pulsar of SN 1987A is that either the high frequency bands of radio telescopes, or the high energy detections at Gamma-ray and X-ray bands by space satellites are applied.     

Atmospheres and spectra of strongly magnetized neutron stars

We construct atmosphere models for strongly magnetized neutron stars with surface fields     and effective temperatures     . The atmospheres directly determine the characteristics of thermal emission from isolated neutron stars, including radio pulsars, soft gamma-ray repeaters, and anomalous X-ray pulsars. In our models, the atmosphere is composed of pure hydrogen or helium and is assumed to be fully ionized. The radiative opacities include free–free absorption and scattering by both electrons and ions computed for the two photon polarization modes in the magnetized electron–ion plasma. Since the radiation emerges from deep layers in the atmosphere with     , plasma effects can significantly modify the photon opacities by changing the properties of the polarization modes. In the case where the magnetic field and the surface normal are parallel, we solve the full, angle-dependent, coupled radiative transfer equations for both polarization modes. We also construct atmosphere models for general field orientations based on the diffusion approximation of the transport equations and compare the results with models based on full radiative transport. In general, the emergent thermal radiation exhibits significant deviation from blackbody, with harder spectra at high energies. The spectra also show a broad feature     around the ion cyclotron resonance     , where Z and A are the atomic charge and atomic mass of the ion, respectively; this feature is particularly pronounced when     . Detection of the resonance feature would provide a direct measurement of the surface magnetic fields on magnetars.