Remnants of compact binary mergers

We investigate the long-term evolution and observability of remnants originating from the merger of compact binary systems and discuss the differences to supernova remnants. Compact binary mergers expel much smaller amounts of mass at much higher velocities, as compared to supernovae, which will affect the dynamical evolution of their remnants. The ejecta of mergers consist of very neutron rich nuclei. Some of these neutron rich nuclei will produce observational signatures in form of gamma ray lines during their decay. The composition of the ejecta might even give interesting constraints about the internal structure of the neutron star. We further discuss the possibility that merger remnants appear as recently discovered ‘dark accelerators’ which are extended TeV sources which lack emission in other bands.     

Production and evolution of millisecond X-ray and radio pulsars

Observations using the Rossi X-ray Timing Explorer (RXTE) have discovered dozens of accreting neutron stars with millisecond spin periods in low-mass binary star systems. Eighteen are millisecond X-ray pulsars powered by accretion or nuclear burning or both. These stars have magnetic fields strong enough for them to become millisecond rotation-powered (radio) pulsars when accretion ceases. Few, if any, accretion- or rotation-powered pulsars have spin rates higher than 750 Hz. There is strong evidence that the spin-up of some accreting neutron stars is limited by magnetic spin-equilibrium whereas the spin-up of others is halted when accretion ends. Further study will show whether the spin rates of some accretion- or rotation-powered pulsars are or were limited by emission of gravitational radiation.     

Expanding shells of young pulsars as sources of high-energy neutrinos

The initial power outputs P_o of pulsars are not yet well known, but these seem to follow approximately a distribution law N(> P_o) ∝ P_o⁻ⁿ where 0.5 ≤ n ≤ 1.0. It seems likely that P_o ≥ 10³⁸ ergs/sec. With these assumptions, we estimate that the DUMAND detector can record ≥ 10³ high-energy (> 4 TeV) neutrino events in a four-month period per Galactic supernova; (in our Galaxy, these are estimated to occur at the rate of about 8 per century.) Neutrinos from supernova shells in the Virgo supercluster would be marginally detectable (one very bright supernova per decade at about 20 Mpc) if N(> P_o) ∝ P_o^−0.5, but undetectable if N(> P_o) ∝ P_o⁻¹. The diffuse flux summed over distant extragalactic supernovae is likely to be well below the detection threshold.     

Infrared radiation from compact X-ray sources

Observations of the X-ray binaries 4U 0115+634 and A 0535+262 performed in 1981 – 1982 revealed significant IR variabilities of these sources. 4U 0115+634 was observed twice, in the state close to X-ray activity, and in the state of low activity, thus changing from K = 7^m.75 to K > 9^m. A 0535+262 shows the temporal variations ranged from tens minutes to some days. The regular variations of IR brightness are suspected with teh period close to 104 s that corresponds to the period of axial rotation of neutron star in A 0535+262. The results obtained present arguments in favour of hypothesis that IR radiation is generated near the accreting neutron star and is possibly of maser nature.     

The evolution of the central component in SN 1986J

The unusual core-collapse supernova 1986J, in the nearby spiral NGC 891, is the first modern supernova in which evidence of a compact remnant of the supernova has been seen. This evidence comes from recent VLBI images, which show the emergence of a new radio component in the center of the expanding radio shell. The new component shows an inverted radio spectrum contrasting with that of the shell. The new component is likely radio emission associated with the black-hole or neutron star compact remnant of the explosion, which would mark the first direct observational link between a modern supernova and such a compact remnant. We report here on our recent VLBI images at 22 and 5 GHz, as well as on our monitoring of the integrated radio spectrum of SN 1986J. In the 22 GHz image, the central component is marginally resolved.     

X射线脉冲星4U 1538—52 的时间和能谱特性

本文处理分析了EXOSAT卫星对4U1538-524次中能观测资料,并结合其他观测结果对4U1538-52的时间和能谱特性作了分析和解释:中子星自转仍在减慢;能谱为幂律谱,Tenma卫星以后的观测未见Fe发射线;X射线dip现象可解释为一前景星对中子星的遮掩而形成;X射线爆发在不同的轨道位相出现,持续近1小时;在1keV附近似有一发射线。      

Effect of random nature of cosmic ray sources – Supernova remnants – on cosmic ray intensity fluctuations,anisotropy, and electron energy spectrum

The random nature of sources (the supernova remnants) leads to the fluctuations of cosmic ray intensity in space and time. We calculate the expected fluctuations in a flat-halo diffusion model for particles with energies from 0.1 to 10³ TeV. The data on energy spectra and anisotropy of very high energy protons, nuclei and electrons, and the astronomical data on supernova remnants, the potential sources of cosmic rays, are used to constrain the value of the cosmic-ray diffusion coefficient and its dependence on energy.     

Type I supernovae origin: “Dualistic” hypothesis

Stars that explode as Type I Supernovae (SNI) are white dwarfs with masses practically equal to the Chandrasekhar limit M_ch. These white dwarfs forme either as a result of gas overflow onto a degenerate component in a binary system or due to the evolution of nuclei of the stars whose mass, on the main sequence, was 3 to 7 M_o. The masses of their nuclei are quite close to M_ch. It is convenient to consider three types of stellar evolution 1) “hyperbolic”: masses of nuclei formed as a result of evolution are > M_ch; such evolution ends in a Type II Supernova (SNII) outburst; 2) “parabolic” - masses of nuclei ≈ M_ch, with the evolution ending in an SNI outburst; 3) “elliptical” with nuclei masses < M_ch. The latter type of evolution leads to the formation of planetary nebulae and white dwarfs. A new hypothesis is suggested that explains more frequent occurrence of SNI in irregular galaxies by flashes of star formation.     

MHD interaction of pulsar wind nebulae with SNRs and with the ISM

In the late 1960s the discovery of the Crab pulsar in its associated supernova remnant, launched a new field in supernova remnant research: the study of pulsar-driven or plerionic supernova remnants. In these type of remnants, the relativistic wind emitted by the pulsar, blows a pulsar wind nebula into the interior of its supernova remnant. Now, more then forty years after the discovery of the Crab pulsar, there are more then fifty plerionic supernova remnants known, due to the ever-increasing capacity of observational facilities. These observational studies reveal a Zoo of complex morphologies over a wide range of frequencies, indicating the significance of the interaction between a pulsar wind nebula with its surrounding supernova remnant. A pulsar which gained a kick velocity at birth, will ultimately break outside of its remnant, after which the pulsar wind nebula interacts directly with the interstellar medium. In general these pulsar wind nebulae are bounded by a bow shock, due to the supersonic motion of the pulsar. There are a few examples known of these pulsar-powered bow shocks, a number which is slowly increasing.I will review our current understanding of the different evolutionary stages of a pulsar wind nebula as it is interacting with its associated supernova remnant. Therefore, I will discuss both analytical and more recent numerical (M)HD models. The four main stages of a pulsar wind nebula are: the supersonic expansion stage, the reverse shock interaction stage, the subsonic expansion stage and ultimately the stage when the head of the bubble is bounded by a bow shock, due to the supersonic motion of the pulsar. Ultimately this pulsar wind nebula bow shock will break through its associated remnant, after which the pulsar-powered bow shock will interact directly with the interstellar medium. I will discuss recent numerical models from these type of pulsar wind nebulae and their morphology.     

X-ray radiation from accreting, magnetized neutron stars

A review is given of recent developments in the theory of emission from a magnetized plasma for accreting neutron star conditions. Some observational data on X-ray pulsars are discussed, and present problems are indicated.     

A VLBI search for pulsar wind nebulae in supernovae

We examine recent supernovae which have been observed with very-long-baseline interferometry in order to detect or limit the emission from a possible compact remnant of the explosion. Such a remnant could be a neutron star, generating a pulsar wind nebula, or a black hole with an accretion disk and jets. Four supernovae, and also more than a dozen supernovae or their young remnants in M82, have structure sufficiently resolved to allow useful conclusions as to the strength of the emission from such young neutron stars or black holes. We recently discovered a compact component in the center of SN 1986J’s shell with a spectral luminosity at 15 GHz 200 times that of the Crab Nebula. This is most likely the compact remnant of the explosion, the first and only one found in any modern supernova. For other modern supernovae, the upper limits on the radio spectral luminosities of such young compact remnants range from 180 times that of the Crab Nebula for SN 1979C in M100 in the Virgo cluster to 0.001 times that of the Crab Nebula for SN 1987A in the Large Magellanic Cloud.     

X-ray synchrotron emission from supernova remnants

X-ray synchrotron emission tells us of the highest energy reached by accelerated electrons. In a few supernova remnants (SN 1006, G347.3-0.5) this is the dominant form of X-ray radiation, but in most it is superposed to the dominant thermal emission. Thanks to the spectro-imaging capability of Chandra and XMM-Newton, X-ray synchrotron emission has now been unambiguously detected in most young supernova remnants (Cas A, Tycho, Kepler). It arises in a very thin shell (a few arcsecs) at the blast wave. The thinness of that shell (much broader in the radio domain) implies that the high energy electrons cool down very fast behind the shock. The magnetic field that one deduces from that constraint is more than 100 μG behind the shock.     

The history of SN 1986J and the emergence of a new compact radio component in its center

We review the history of the unusual Type II supernova 1986J in the nearby spiral galaxy NGC 891. A series of VLBI observations have shown the expanding shell structure and allowed the expansion curve to be determined. The integrated radio spectrum and radio lightcurve have also been monitored. The spectrum was a power-law before 1998, after which an inversion appeared above 5 GHz. Our recent high-frequency VLBI observations showed that this inverted-spectrum emission was associated not with the shell emission, but rather with a compact component almost precisely in the center of the expanding shell. The new component is likely radio emission associated with the black-hole or neutron star compact remnant of the explosion, which would mark the first direct observational link between a modern supernova and such a compact remnant.     

The plerionic supernova remnant G21.5-0.9: In and out

The absence of a supernova remnant (SNR) shell surrounding the Crab and other plerions (pulsar wind nebulae) has been a mystery for three decades. G21.5-0.9 is a particularly intriguing plerionic SNR in which the central powering engine is not yet detected. Early CHANDRA observations revealed a faint extended X-ray halo which was suggested to be associated with the SNR shell; however its spectrum was non-thermal, unlike what is expected from an SNR shell. On the other hand, a plerionic origin to the halo is problematic since the X-ray plerion would be larger than the radio plerion. We present here our analysis of an integrated 245 ks of archival CHANDRA data acquired with the High-Resolution Camera (HRC) and 520 ks acquired with the Advanced CCD Imaging Spectrometer (ACIS). This study provides the deepest and highest resolution images obtained to date. The resulting images reveal for the first time: (1) a limb-brightened morphology in the eastern section of the halo, and (2) a rich structure in the inner (40″-radius) bright plerion including wisps and a double-lobed morphology with an axis of symmetry running in the northwest–southeast direction. Our spatially resolved spectroscopic study of the ACIS-I data indicates that the photon index steepens with increasing distance from the central point source out to a radius of 40″ then becomes constant at ∼2.4 in the X-ray halo (for a column density N_H = 2.2 × 10²² cm⁻²). No line emission was found from the eastern limb; however marginal evidence for line emission in the halo’s northern knots was found. This study illustrates the need for deep CHANDRA observations to reveal the missing SNR material in Crab-like plerions.     

X射线脉冲星导航技术研究进展

X射线脉冲星能够为近地轨道、深空和星际空间飞行航天器提供位置、速度、时间和姿态等丰富的导航信息,实现航天器高精度自主导航和运行管理,有着巨大的发展潜力.本文论述了X射线脉冲星导航技术研究历程;重点研究了X射线脉冲星导航的基本原理、信息处理流程和自主导航算法,进而提出了脉冲星导航的关键技术;分析了国内脉冲星观测研究的基础条件,以及开展X射线脉冲星导航技术研究的必要性和可行性.      

The multi-wavelength properties of Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters

This paper reviews the multi-wavelength properties of two groups of pulsars, the Anomalous X-ray Pulsars (AXPs) and the Soft Gamma-ray Repeaters (SGRs), that are generally interpreted as isolated neutron stars with strong magnetic fields of 10¹⁴–10¹⁵ G. Most of these sources have now been observed at different wavelengths, from the radio band to hard X-rays. Several new members of these classes have been discovered in the last few years, due to their transient nature. The distinction between AXPs and SGRs is becoming less evident, as more observations are collected which show similar properties in all these sources.     

New insights into SNR evolution revealed by the discovery of recombining plasmas

We report the discovery of recombining plasmas in three supernova remnants (SNRs) with the Suzaku X-ray astronomy satellite. During SNR’s evolution, the expanding supernova ejecta and the ambient matter are compressed and heated by the reverse and forward shocks to form an X-ray emitting hot plasma. Since ionization proceeds slowly compared to shock heating, most young or middle-aged SNRs have ionizing (underionized) plasmas. Owing to high sensitivity of Suzaku, however, we have detected radiative recombination continua (RRCs) from the SNRs IC 443, W49B, and G359.1–0.5. The presence of the strong RRC is the definitive evidence that the plasma is recombining (overionized). As a possible origin of the overionization, an interaction between the ejecta and dense circumstellar matter is proposed; the highly ionized gas was made at the initial phase of the SNR evolution in dense regions, and subsequent rapid adiabatic expansion caused sudden cooling of the electrons. The analysis on the full X-ray band spectrum of IC 443, which is newly presented in this paper, provides a consistent picture with this scenario. We also comment on the implications from the fact that all the SNRs having recombining plasmas are correlated with the mixed-morphology class.     

基于UKF和信息融合的航天器自主导航方法

X射线脉冲星导航利用X射线辐射脉冲到达时间 (Time of Arrival, TOA)作为信息输入,星敏感器导航利用星光角距等作为信息输入,是两种不同机理的天文导航方法。提出一种将脉冲星TOA和星敏感器星光角距测量结合的信息融合天文自主导航方法,设计了一种利用激光光量子模拟脉冲星X射线辐射光子的半物理仿真系统用于算法验证,并基于无迹卡尔曼滤波(Unscented Kalman Filter, UKF)使用真轨道参数做了仿真试验。结果表明,基于UKF的信息融合方法比基于EKF（Extended Kalman Filter）的信息融合方法性能更好,与仅使用脉冲星或星敏感器的导航方法相比,能将位置估计精度分别提高52.7%和43.6%,速度估计精度分别提高82.2%和70.5%。     

Theromonuclear flashes in accreting neutron star envelopes

The thermonuclear model for x-ray burster and “soft transient” is discussed. The mass accretion rate M, the chemical composition of accreted matter, the gravitational potential of the neutron star and thermal state of outer layer / or core/ are the main parameters which determine the burning regime. Importance of nuclear network used for the properties of subsequent flashes is pointed out.     

Interplanetary spacecraft navigation using pulsars

We demonstrate how observations of pulsars can be used to help navigate a spacecraft travelling in the solar system. We make use of archival observations of millisecond pulsars from the Parkes radio telescope in order to demonstrate the effectiveness of the method and highlight issues, such as pulsar spin irregularities, which need to be accounted for. We show that observations of four millisecond pulsars every seven days using a realistic X-ray telescope on the spacecraft throughout a journey from Earth to Mars can lead to position determinations better than ∼20 km and velocity measurements with a precision of ∼0.1 ms⁻¹.