A test of general relativity from the three-dimensional orbital geometry of a binary pulsar.

Binary pulsars provide an excellent system for testing general relativity because of their intrinsic rotational stability and the precision with which radio observations can be used to determine their orbital dynamics. Measurements of the rate of orbital decay of two pulsars have been shown to be consistent with the emission of gravitational waves as predicted by general relativity, but independent verification was not possible. Such verification can in principle be obtained by determining the orbital inclination in a binary pulsar system using only classical geometrical constraints. This would permit a measurement of the expected retardation of the pulse signal arising from the general relativistic curvature of space-time in the vicinity of the companion object (the 'Shapiro delay'). Here we report high-precision radio observations of the binary millisecond pulsar PSR J0437-4715, which establish the three-dimensional structure of its orbit. We see the Shapiro delay predicted by general relativity, and we determine the mass of the neutron star and its white dwarf companion. The determination of such masses is necessary in order to understand the origin and evolution of neutron stars.     

Transient pulsed radio emission from a magnetar

Anomalous X-ray pulsars (AXPs) are slowly rotating neutron stars with very bright and highly variable X-ray emission that are believed to be powered by ultra-strong magnetic fields of >10(14) G, according to the 'magnetar' model. The radio pulsations that have been observed from more than 1,700 neutron stars with weaker magnetic fields have never been detected from any of the dozen known magnetars. The X-ray pulsar XTE J1810-197 was revealed (in 2003) as the first AXP with transient emission when its luminosity increased 100-fold from the quiescent level; a coincident radio source of unknown origin was detected one year later. Here we show that XTE J1810-197 emits bright, narrow, highly linearly polarized radio pulses, observed at every rotation, thereby establishing that magnetars can be radio pulsars. There is no evidence of radio emission before the 2003 X-ray outburst (unlike ordinary pulsars, which emit radio pulses all the time), and the flux varies from day to day. The flux at all radio frequencies is approximately equal--and at >20 GHz XTE J1810-197 is currently the brightest neutron star known. These observations link magnetars to ordinary radio pulsars, rule out alternative accretion models for AXPs, and provide a new window into the coronae of magnetars.     

A debris disk around an isolated young neutron star

Pulsars are rotating, magnetized neutron stars that are born in supernova explosions following the collapse of the cores of massive stars. If some of the explosion ejecta fails to escape, it may fall back onto the neutron star or it may possess sufficient angular momentum to form a disk. Such 'fallback' is both a general prediction of current supernova models and, if the material pushes the neutron star over its stability limit, a possible mode of black hole formation. Fallback disks could dramatically affect the early evolution of pulsars, yet there are few observational constraints on whether significant fallback occurs or even the actual existence of such disks. Here we report the discovery of mid-infrared emission from a cool disk around an isolated young X-ray pulsar. The disk does not power the pulsar's X-ray emission but is passively illuminated by these X-rays. The estimated mass of the disk is of the order of 10 Earth masses, and its lifetime (> or = 10(6) years) significantly exceeds the spin-down age of the pulsar, supporting a supernova fallback origin. The disk resembles protoplanetary disks seen around ordinary young stars, suggesting the possibility of planet formation around young neutron stars.     

Nuclear-powered millisecond pulsars and the maximum spin frequency of neutron stars

Millisecond pulsars are neutron stars that are thought to have been spun-up by mass accretion from a stellar companion. It is not known whether there is a natural brake for this process, or if it continues until the centrifugal breakup limit is reached at submillisecond periods. Many neutron stars that are accreting mass from a companion star exhibit thermonuclear X-ray bursts that last tens of seconds, caused by unstable nuclear burning on their surfaces. Millisecond-period brightness oscillations during bursts from ten neutron stars (as distinct from other rapid X-ray variability that is also observed) are thought to measure the stellar spin, but direct proof of a rotational origin has been lacking. Here we report the detection of burst oscillations at the known spin frequency of an accreting millisecond pulsar, and we show that these oscillations always have the same rotational phase. This firmly establishes burst oscillations as nuclear-powered pulsations tracing the spin of accreting neutron stars, corroborating earlier evidence. The distribution of spin frequencies of the 11 nuclear-powered pulsars cuts off well below the breakup frequency for most neutron-star models, supporting theoretical predictions that gravitational radiation losses can limit accretion torques in spinning up millisecond pulsars.     

Magnetar-like X-ray bursts from an anomalous X-ray pulsar

Anomalous X-ray pulsars (AXPs) are a class of rare X-ray emitting pulsars whose energy source has been perplexing for some 20 years. Unlike other X-ray emitting pulsars, AXPs cannot be powered by rotational energy or by accretion of matter from a binary companion star, hence the designation 'anomalous'. Many of the rotational and radiative properties of the AXPs are strikingly similar to those of another class of exotic objects, the soft-gamma-ray repeaters (SGRs). But the defining property of the SGRs--their low-energy-gamma-ray and X-ray bursts--has not hitherto been observed for AXPs. Soft-gamma-ray repeaters are thought to be 'magnetars', which are young neutron stars whose emission is powered by the decay of an ultra-high magnetic field; the suggestion that AXPs might also be magnetars has been controversial. Here we report two X-ray bursts, with properties similar to those of SGRs, from the direction of the anomalous X-ray pulsar 1E1048.1 - 5937. These events imply a close relationship (perhaps evolutionary) between AXPs and SGRs, with both being magnetars.     

The geometry of the double-pulsar system J0737-3039 from systematic intensity variations

Two pulsars (PSR J0737-3039A and B) were recently discovered in highly relativistic orbits around one another. The system contains a rapidly rotating pulsar with a spin period of 22.7 ms and a slow companion with a spin period of 2.77 s, referred to here as 'A' and 'B', respectively. A unique property of the system is that the pulsed radio flux from B increases systematically by almost two orders of magnitude during two short portions of its orbit. Here we report a geometrical model of the system that simultaneously explains the intensity variations of B and provides constraints on the spin axis orientation and emission geometry of A. Our model assumes that B's pulsed radio flux increases when illuminated by emission from A. We predict that A's pulse profile will evolve considerably over the next several years owing to geodetic precession until it disappears entirely in 15-20 years.     

一个脉冲星模式变化的观测和研究

用我国自行研制的脉冲星观测系统在新疆乌鲁木齐天文站２５ｍ天线上成功地观测了８颗脉冲星,并观测到ＰＳＲ１１３３＋１６的模式变化现象,就脉冲星模式变化总题进行一些探讨。     

脉冲星与夸克星

简要地回顾了脉冲星、中子星和夸克星的研究历史;总结了当前(特别是笔者所在研究小组)对于夸克星研究的进展并指出所面临的主要问题,特别讨论了区分普通中子星和夸克星的可能途径;给出了一些夸克星候选体以及未来可能的观测检验。     

"中子星"研究的挑战

脉冲星(PSRs)被发现之后,很快地就被证认为中子星(NSs),关于它们的研究极大地丰富了人们对于自然的认识.由于第一颗射电脉冲星的发现以及对强引力场下广义相对论的检验,脉冲星研究者已经两次获得了诺贝尔物理学奖.最近,"中子星"家族中的一些新种类被发现了,它们是:所谓的软伽马射线重复爆(SGRs),反常X射线脉冲星(AXPs),超新星遗迹(SNRs)中的致密中心天体(CCOs)和暗弱热中子星(DTNs).这对理论家们提出了如下的挑战:是否部分或者全部的所谓"中子星"的本质实际上是"奇异星(SSs)"?是否存在所谓的"磁星"(一种具有超强磁场的中子星)?本文论述了"中子星"的观测特性,为理解它们本质所作的理论努力以及不同模型间的争论(尤其是关于SGRs和AXPs).     

Nanosecond radio bursts from strong plasma turbulence in the Crab pulsar

The Crab pulsar was discovered by the occasional exceptionally bright radio pulses it emits, subsequently dubbed 'giant' pulses. Only two other pulsars are known to emit giant pulses. There is no satisfactory explanation for the occurrence of giant pulses, nor is there a complete theory of the pulsar emission mechanism in general. Competing models for the radio emission mechanism can be distinguished by the temporal structure of their coherent emission. Here we report the discovery of isolated, highly polarized, two-nanosecond subpulses within the giant radio pulses from the Crab pulsar. The plasma structures responsible for these emissions must be smaller than one metre in size, making them by far the smallest objects ever detected and resolved outside the Solar System, and the brightest transient radio sources in the sky. Only one of the current models--the collapse of plasma-turbulent wave packets in the pulsar magnetosphere--can account for the nanopulses we observe.     

Transient radio bursts from rotating neutron stars

The radio sky is relatively unexplored for transient signals, although the potential of radio-transient searches is high. This was demonstrated recently by the discovery of a previously unknown type of source, varying on timescales of minutes to hours. Here we report a search for radio sources that vary on much shorter timescales. We found eleven objects characterized by single, dispersed bursts having durations between 2 and 30 ms. The average time intervals between bursts range from 4 min to 3 h with radio emission typically detectable for <1 s per day. From an analysis of the burst arrival times, we have identified periodicities in the range 0.4-7 s for ten of the eleven sources, suggesting origins in rotating neutron stars. Despite the small number of sources detected at present, their ephemeral nature implies a total Galactic population significantly exceeding that of the regularly pulsing radio pulsars. Five of the ten sources have periods >4 s, and the rate of change of the pulse period has been measured for three of them; for one source, we have inferred a high magnetic field strength of 5 x 10(13) G. This suggests that the new population is related to other classes of isolated neutron stars observed at X-ray and gamma-ray wavelengths.     

Optical pulsations from the anomalous X-ray pulsar 4U0142+61

Anomalous X-ray pulsars (AXPs) differ from ordinary radio pulsars in that their X-ray luminosity is orders of magnitude greater than their rate of rotational energy loss, and so they require an additional energy source. One possibility is that AXPs are highly magnetized neuron stars or 'magnetars' having surface magnetic fields greater than 10(14) G. This would make them similar to the soft gamma-ray repeaters (SGRs), but alternative models that do not require extreme magnetic fields also exist. An optical counterpart to the AXP 4U0142+61 was recently discovered, consistent with emission from a magnetar, but also from a magnetized hot white dwarf, or an accreting isolated neutron star. Here we report the detection of optical pulsations from 4U0142+61. The pulsed fraction of optical light (27 per cent) is five to ten times greater than that of soft X-rays, from which we conclude that 4U0142+61 is a magnetar. Although this establishes a direct relationship between AXPs and the soft gamma-ray repeaters, the evolutionary connection between AXPs, SGRs and radio pulsars remains controversial.     

Flares from a candidate Galactic magnetar suggest a missing link to dim isolated neutron stars

Magnetars are young neutron stars with very strong magnetic fields of the order of 10(14)-10(15) G. They are detected in our Galaxy either as soft gamma-ray repeaters or anomalous X-ray pulsars. Soft gamma-ray repeaters are a rare type of gamma-ray transient sources that are occasionally detected as bursters in the high-energy sky. No optical counterpart to the gamma-ray flares or the quiescent source has yet been identified. Here we report multi-wavelength observations of a puzzling source, SWIFT J195509+261406. We detected more than 40 flaring episodes in the optical band over a time span of three days, and a faint infrared flare 11 days later, after which the source returned to quiescence. Our radio observations confirm a Galactic nature and establish a lower distance limit of approximately 3.7 kpc. We suggest that SWIFT J195509+261406 could be an isolated magnetar whose bursting activity has been detected at optical wavelengths, and for which the long-term X-ray emission is short-lived. In this case, a new manifestation of magnetar activity has been recorded and we can consider SWIFT J195509+261406 to be a link between the 'persistent' soft gamma-ray repeaters/anomalous X-ray pulsars and dim isolated neutron stars.     

Δ共振态存在于中子星内部的可能性探讨

本文通过相对论平均场理论和Tolman-Oppenheimer-Volkoff方程来研究中子星的微观和宏观性质。与最新的脉冲星J1614-2230的观测数据作比照,可以发现除了传统的中子星物质外,Δ共振态中的Δ-和Δ0粒子也很可能大量存在于PSR J1614-2230的内部。另外,也进一步探讨了Δ共振态对中子星所产生的影响。     

gamma Rays from close binaries in the quiet stage

THE presence of rotating neutron stars in binary systems is revealed by the existence of X-ray pulsators which are generally associated with massive companions. The evolutionary history of these systems is now relatively clear (see ref. 1 and refs therein). The X-ray phase, which corresponds to accretion on the neutron star of a strong stellar wind \M approximately 10(-6) M(\circ) yr(-1), is preceded by a much longer quiet state, where the primary is unevolved, possibly with a weak wind, \M approximately 10(-9) M(\circ) yr(-1) and the rotational energy loss of the neutron star inhibits accretion. However, with the only exception of PSR1913 + 16, radio pulsars are not found in binary systems. Here, motivated by the recent discovery of gamma-ray emission from slow pulsars(2,3), we suggest (gamma)-ray observations as a way of detecting binaries in the quiet state and compare the expected number with the COS B results. We refer to the review of van den Heuvel(1) where, as a representative case, a system of initial mass 20 + 8 M(\circ) and orbital period 4.7 d is considered. After the first stage of mass exchange and the supernova explosion, one has a neutron star with an unevolved companion of 22.7 M(\circ). The period is now P = 12.6 d. The primary remains on the main sequence (quiet stage) for t(ms) = 3.6 x 10(6)yr. The X-ray phase occurs after the star has left the main sequence, but before it fills its Roche lobe, as an excessive mass transfer absorbs the X-ray emission. Its duration is t(x) approximately 10(4)yr.     

在脉冲星的观测证据中寻找夸克解禁态

简述了中子星结构、组成、演化的理论研究以及相关的观测进展,对演化后期孤立毫秒脉冲星和处于双星系统中的脉冲星可能存在夸克解禁和夸克重囚禁的现象进行了理论上和观测证据上的探讨。认为双星系统中的脉冲星可能会由于条件不同,会分别出现夸克解禁和夸克重囚禁的现象。     

Very fast optical flaring from a possible new Galactic magnetar

Highly luminous rapid flares are characteristic of processes around compact objects like white dwarfs, neutron stars and black holes. In the high-energy regime of X-rays and gamma-rays, outbursts with variabilities on timescales of seconds or less are routinely observed, for example in gamma-ray bursts or soft gamma-ray repeaters. At optical wavelengths, flaring activity on such timescales has not been observed, other than from the prompt phase of one exceptional gamma-ray burst. This is mostly due to the fact that outbursts with strong, fast flaring are usually discovered in the high-energy regime; most optical follow-up observations of such transients use instruments with integration times exceeding tens of seconds, which are therefore unable to resolve fast variability. Here we show the observation of extremely bright and rapid optical flaring in the Galactic transient SWIFT J195509.6+261406. Our optical light curves are phenomenologically similar to high-energy light curves of soft gamma-ray repeaters and anomalous X-ray pulsars, which are thought to be neutron stars with extremely high magnetic fields (magnetars). This suggests that similar processes are in operation, but with strong emission in the optical, unlike in the case of other known magnetars.     

脉冲星发现55年：中国天眼展望

 脉冲星的发现是人类认识宇宙的重要里程碑之一。介绍了脉冲星自发现至今55年来的研究进展，包括引力波与广义相对论的验证、毫秒脉冲星、脉冲星周期跃变、脉冲星射电辐射效率、快速射电暴与河外脉冲星等方面。展望了中国天眼（FAST）未来发现新的特殊类型脉冲星的潜力，如黑洞脉冲星系统/亚毫秒脉冲星/新型双脉冲星系统，依此实施更高精度验证引力波实验；利用FAST的高灵敏度、高精度研究脉冲星辐射的精细结构，深入了解其物理机制。     

Profile of the composition fractions in neutron stars

The composition fractions of β-stable neutron stars and their radial distributions are investigated based on Skyrme-Hartree-Fock theory and Tolman-Oppenheimer-Volkoff (TOV) equation. It is found that a pure neutron interior with a radius of 3.5 km can exist in the neutron stars. When the radius is greater than 3.5 km, the fractions of the proton, electron and μ⁻ appear and increase with the increment of the radius, then decrease after reaching their maximum at the radius of 8 km. These results make it possible to further study the thermal evolution and magnetic properties of the neutron stars.     

基于贝叶斯推断的脉冲星偏振位置角拟合算法

脉冲星辐射束的偏振位置角与相位的关系可用旋转矢量模型(RVM)描述,现有的Levenberg-Marquardt非线性拟合和格点搜寻算法对RVM的拟合存在效率低、易过拟合等问题。本文发展了一套基于贝叶斯推断的马尔可夫链蒙特卡洛算法(MCMC),并用该方法对已有文献中的10颗脉冲星偏振位置角进行了拟合。结果表明,MCMC算法不仅能得到与已有文献一致的结果,而且该算法具有高效、不易过拟合、能更好地估计参数的可信度区间等优点。