SLX 1746-311 in outburst

We report on RXTE-PCA observations of SLX 1746-311 during a 100 day outburst in April 2003. We present the 3–20 keV PCA energy spectra of the source and study evolution of spectral parameters. The burst spectrum is soft with T_in 1.3 keV at the beginning of the outburst. There is a clear evidence of a hard power law component throughout the outburst. There is also an indication of a broad iron line. The source exhibits three state transitions with considerable change in the hardness ratio at low count rates. We discuss the possible scenario under which this unusual behaviour can be explained.     

Orbital phase spectroscopy of X-ray pulsars to study the stellar wind of the companion

High Mass X-ray Binary Pulsars (HMXBP), in which the companion star is a source of supersonic stellar wind, provide a laboratory to probe the velocity and density profile of such winds. Here, we have measured the variation of the absorption column density along with other spectral parameters over the binary orbit for two HMXBP in elliptical orbits, as observed with the Rossi X-ray Timing Explorer (RXTE) and the BeppoSAX satellites. A spherically symmetric wind profile was used as a model to compare the observed column density variations. In 4U 1538-52, we find the model corroborating the observations; whereas in GX 301-2, the stellar wind appears to be very clumpy and a smooth symmetric wind model seems to be inadequate in explaining the variation in column density.     

A highly-ionized absorber as a new explanation for the spectral changes during dips from X-ray binaries

We report the XMM-Newton detection of narrow Fe xxv and Fe xxvi X-ray absorption lines at 7 keV in the persistent emission of the dipping low-mass X-ray binary (LMXB) 4U 1323−62. Such features have now been reported in a growing number of LMXBs seen almost edge-on, indicating that the highly-ionized plasma probably originates in an accretion disk atmosphere or wind. During dipping intervals of 4U 1323−62, the strength of the Fe xxv feature increases while that of the Fe xxvi feature decreases, consistent with the presence of less strongly ionized material in the line-of-sight. As observed previously, the changes in the X-ray spectrum during dips are inconsistent with a simple increase in absorption by cool material. However, we show that the changes in both the narrow absorption features and the continuum can be modeled self-consistently by variations in the properties of an ionized absorber. From persistent to deep dipping the photo-ionization parameter decreases while the equivalent hydrogen column density of the ionized absorber increases. No partial covering of any component of the spectrum, and hence no extended corona, are required. Since highly-ionized absorption features are seen from many other dip sources, this mechanism may also explain the overall changes in X-ray spectrum observed during dipping intervals from these systems.     

Phase resolved study of the CRSF in MX 0656-072

MXB 0656-072 is an accreting X-ray pulsar with a Be star companion, showing notable emission in H. In October 2003 this system exhibited a large and extended X-ray outburst. RXTE observations during this outburst indicated a pulse period of 160.4 s and a cyclotron resonance scattering feature in the spectrum at 32 keV. This paper presents pulse profile analysis and phase-resolved X-ray spectroscopy of RXTE observations during this outburst.     

Composite profile of the Fe Kα spectral line emitted from a binary system of supermassive black holes

We used a model of a relativistic accretion disk around a supermassive black hole (SMBH), based on ray-tracing method in the Kerr metric, to study the variations of the composite Fe Kα line emitted from two accretion disks around SMBHs in a binary system. We assumed that the orbit of such a binary is approximately Keplerian, and simulated the composite line shapes for different orbital elements, accretion disk parameters and mass ratios of the components. The obtained results show that, if observed in the spectra of some SMBH binaries during their different orbital phases, such composite Fe Kα line profiles could be used to constrain the orbits and several properties of such SMBH binaries.     

RadioAstron orbit determination and evaluation of its results using correlation of space-VLBI observations

A crucial part of a space mission for very-long baseline interferometery (VLBI), which is the technique capable of providing the highest resolution images in astronomy, is orbit determination of the mission’s space radio telescope(s). In order to successfully detect interference fringes that result from correlation of the signals recorded by a ground-based and a space-borne radio telescope, the propagation delays experienced in the near-Earth space by radio waves emitted by the source and the relativity effects on each telescope’s clock need to be evaluated, which requires accurate knowledge of position and velocity of the space radio telescope. In this paper we describe our approach to orbit determination (OD) of the RadioAstron spacecraft of the RadioAstron space-VLBI mission. Determining RadioAstron’s orbit is complicated due to several factors: strong solar radiation pressure, a highly eccentric orbit, and frequent orbit perturbations caused by the attitude control system. We show that in order to maintain the OD accuracy required for processing space-VLBI observations at cm-wavelengths it is required to take into account the additional data on thruster firings, reaction wheel rotation rates, and attitude of the spacecraft. We also investigate into using the unique orbit data available only for a space-VLBI spacecraft, i.e. the residual delays and delay rates that result from VLBI data processing, as a means to evaluate the achieved OD accuracy. We present the results of the first experience of OD accuracy evaluation of this kind, using more than 5000 residual values obtained as a result of space-VLBI observations performed over 7 years of the RadioAstron mission operations.     

Orbital phase spectroscopy of four high mass X-ray binary pulsars to study the stellar wind of the companion

Our work focuses on a comprehensive orbital phase-dependent spectroscopy of the four High Mass X-ray Binary Pulsars (HMXBPs) 4U 1538-52, GX 301-2, OAO 1657-415 and Vela X-1. We hereby report the measurements of the variation of the absorption column density and iron-line flux along with other spectral parameters over the binary orbit for the above-mentioned HMXBPs in elliptical orbits, as observed with the Rossi X-ray Timing Explorer (RXTE) and the BeppoSAX satellites. A spherically symmetric wind profile was used as a model to compare the observed column density variations. Out of the four pulsars, only in 4U 1538-52, we find the model having a reasonable corroboration with the observations, whereas in the remaining three the stellar wind seems to be clumpy and a smooth symmetric stellar wind model appears to be quite inadequate in explaining the data. Moreover, in GX 301-2, neither the presence of a disk nor a gas stream from the companion was validated. Furthermore, the spectral results obtained in the case of OAO 1657-415 and Vela X-1 were more or less similar to that of GX 301-2.     

Black hole spectral states and physical connections

The dramatic changes seen in the X-ray spectral and timing properties of accreting black hole candidates (BHCs) provide important clues about the accretion and jet formation processes that occur in these systems. Dividing the different source behaviors into spectral states provides a framework for studying BHCs. To date, there have been three main classification schemes with Luminosity-based, Component-based, or Transition-based criteria. The canonical, Luminosity-based criteria and physical models that are based on this concept do not provide clear explanations for several phenomena, including hysteresis of spectral states and the presence of jets. I discuss the re-definitions of states, focusing on an application of the Component-based states to more than 400 RXTE observations of the recurrent BHC 4U 1630–47. We compare the X-ray properties for the recent 2002–2004 outburst to those of an earlier (1998) outburst, during which radio jets were observed. The results suggest a connection between hysteresis of states and major jet ejections, and it is possible that both of these are related to the evolution of the inner radius of the optically thick accretion disk.     

空间碎片环境与碰撞预警仿真系统设计

在轨编目航天器数目已超过了9000,为了保证航天任务的顺利完成,必须对可能威胁到任务轨道的空间目标进行分析,文章首先对两行轨道根数和SGP4／SDP4轨道预报模型进行了分析,在此基础上建立了空间目标数据库及空间碎片环境与碰撞预警仿真和数据可视化系统。     

The revised eccentric binary model for X Persei (4U 0352 + 30)

The eccentric binary model for X Persei is discussed with a view to most recent determination of mass, radius and mass loss rate. The existence of such a system depends critically on the value of viscosity in the outer layers of the star and, in the case where viscosity is induced by shear turbolence, on the axial rotational velocity. The parameters of the binary system are derived in the most favourable case.     

Modeling and analysis of Earth’s gravity field measurement performance by inner-formation flying system

The Earth’s gravity field can be measured with high precision by constructing the purely gravitational orbit of the inner-satellite in Inner-formation Flying System (IFS), which is independently proposed by Chinese scholars and offers a new way to carry out gravity field measurement by satellite without accelerometers. In IFS, for the purpose of quickly evaluating the highest degree of recovered gravity field model and geoid error as well as analyzing the influence of system parameters on gravity field measurement, an analytical formula was established by spectral analysis method. The formula can reflect the analytical relationship between gravity field measurement performance and system parameters such as orbit altitude, the inner-satellite orbit determination error, the inner-satellite residual disturbances, data sampling interval and total measurement time. This analytical formula was then corrected by four factors introduced from numerical simulation of IFS gravity field measurement. By comparing computation results from corrected analytical formula and the actual gravity field measurement performance by CHAMP, the correctness and rationality of this analytical formula were verified. Based on this analytical formula, the influences of system parameters on IFS gravity field measurement were analyzed. It is known that gravity field measurement performance is a monotone decreasing function of orbit altitude, the inner-satellite orbit determination error, the inner-satellite residual disturbances, data sampling interval and the reciprocal of total measurement time. There is a match relationship between the inner-satellite orbit determination error and residual disturbances, in other words, the change rate of gravity field measurement performance with one of them is seriously restricted by their relative size. The analytical formula can be used to quantitatively evaluate gravity field measurement performance fast and design IFS parameters optimally. It is noted that the analytical formula and corresponding conclusions are applied to any gravity satellite which measures gravity field by satellite perturbation orbit.     

Einstein observations of high luminosity X-ray binaries

Recent observational advances in the study of high luminosity x-ray binaries have permitted investigation of the interaction of the outgoing x-radiation with the accreting matter surrounding the compact object. In two sources, 4U1822-37 and 4U2129+47, extended EINSTEIN coverage has led to the detection of partial x-ray eclipses, which indicate that the x-ray emitting regions must be extended in size. These have been interpreted as evidence for a large Compton-thick corona produced by evaporation of cool material off the surface of an accretion disk. In three other sources, 4U1915-05, 4U1624-49, and Cygnus X-2, evidence has been found for short x-ray absorption dips which are likely to be associated with obscuration by cool dense matter at the outer edge of the disk. In 4U1915-05, these dips are strictly periodic and determine the binary period for the system. In Cygnus X-2, the dips appear to be quasiperiodic, while in 4U1624-49, insufficient coverage has prevented clarification of the temporal properties of the absorption.For the brightest cosmic x-ray source, Scorpius X-1, the EINSTEIN objective grating spectrometer has provided high resolution spectra (λ/Δλ ～50) in the wavelength range 40-10 Å. The spectra reveal absorption features due to intervening helium, nitrogen, and oxygen. The implied nitrogen and oxygen abundances are anomalous and suggest that the absorbing material is intrinsic accreting matter which has been transferred from the surface of an evolved companion. Constraints on the inclination of the system then imply that this cool dense material must be well out of the orbital plane of the binary.     

‘Spectro-temporal’ characteristics and disk-jet connection of the outbursting black hole source XTE J1859+226

We re-investigated the ‘spectro-temporal’ behavior of the source XTE J1859+226 in X-rays during its outburst phase in 1999, by analysing the RXTE PCA/HEXTE data in 2–150 keV spectral band. Detailed analysis shows that the source evolves through different spectral states during its entire outburst as indicated by the variation in the spectral and temporal characteristics. Although the evolution pattern of the outburst followed the typical q-shaped profile, we observed an absence of ‘canonical’ soft state and a weak presence of ‘secondary’ emission during the decay phase of the outburst. The broad-band spectra, modeled with high energy cutoff, shows that the fold-energy increases monotonically in the hard and hard-intermediate states followed by a random variation in the soft-intermediate state. We attempted to estimate the mass of the source based on the evolution of Quasi-Periodic Oscillation (QPO) frequencies during rising phase modeled with the propagating oscillatory shock solution, and from the correlation of photon index and QPO frequency. It is also observed that during multiple ejections (observed as radio flares) the QPO frequencies are not present in the power spectra and there is an absence of lag in the soft to hard photons. The disk flux increases along with a decrease in the high energy flux, implying the soft nature of the spectrum. These results are the ‘possible’ indication that the inner part of the disk (i.e., Comptonized corona), which could be responsible for the generation of QPO and for the non-thermal Comptonized component of the spectrum, is disrupted and the matter gets evacuated in the form of jet. We attempted to explain the complex behavior of ‘spectro-temporal’ properties of the source during the entire outburst and the nature of the disk-jet connection before, during and after the ejection events in the context of two different types of accreting flow material, in presence of magnetic field.     

椭圆轨道编队的构形变化控制方法

推导了椭圆轨道编队的一些典型构形模态,指出椭圆轨道卫星编队的模态不同于圆轨道的构形模态,是极为丰富的。基于T-H方程的解析解,推导了副星在沿航向常值推力作用下的椭圆轨道编队的构形变化控制方法。推导的构形变化控制方法,通过合理的选择控制量的作用时刻,可达到大量节约燃料的目的。最后,给出仿真算例。     

Evaluation of the dynamic cutoff rigidity model using dosimetry data from the STS-28 flight.

We have a developed a dynamic cutoff rigidity model based on computed world grids of vertical cutoff rigidities derived from employing the Tsyganenko magnetospheric model. The dynamic range of this model covers all magnetic activity levels specified by integer values of the Kp magnetic index. We present comparisons of the measured dose observed on the space shuttle during the August 1989 solar proton event with the dose computed from solar particles predicted to be allowed through the magnetosphere to the space shuttle position. We find a one-to-one correspondence between the portion of the orbit predicted to be subjected to solar protons and the portion of the orbit where solar particle dose measurements were obtained.     

Heliotropic dust rings for Earth climate engineering

This paper examines the concept of a Sun-pointing elliptical Earth ring comprised of dust grains to offset global warming. A new family of non-Keplerian periodic orbits, under the effects of solar radiation pressure and the Earth’s J₂ oblateness perturbation, is used to increase the lifetime of the passive cloud of particles and, thus, increase the efficiency of this geoengineering strategy. An analytical model is used to predict the orbit evolution of the dust ring due to solar-radiation pressure and the J₂ effect. The attenuation of the solar radiation can then be calculated from the ring model. In comparison to circular orbits, eccentric orbits yield a more stable environment for small grain sizes and therefore achieve higher efficiencies when the orbit decay of the material is considered. Moreover, the novel orbital dynamics experienced by high area-to-mass ratio objects, influenced by solar radiation pressure and the J₂ effect, ensure the ring will maintain a permanent heliotropic shape, with dust spending the largest portion of time on the Sun facing side of the orbit. It is envisaged that small dust grains can be released from a circular generator orbit with an initial impulse to enter an eccentric orbit with Sun-facing apogee. Finally, a lowest estimate of 1 × 10¹² kg of material is computed as the total mass required to offset the effects of global warming.     

Navigating BepiColombo during the weak-stability capture at Mercury

BepiColombo is scheduled for launch in August 2013 and to arrive after a nearly six-year long transfer at Mercury in June 2019. The trajectory has a number of challenging elements: a launch with Soyuz/Fregat into a geostationary transfer orbit, followed by a lunar flyby, long low-thrust arcs and five more planetary flybys (one at the Earth, two at Venus and two at Mercury). At arrival the low thrust arcs reduce the approach velocity so much that BepiColombo passes by the Sun–Mercury Lagrange points L₁ and L₂ and gets weakly captured in a highly eccentric orbit around Mercury in case the orbit insertion manoeuvre would fail.This paper describes the navigation strategy during the final phase. Five trajectory correction manouevres during the last 65 days requiring up to 20 m/s (3σ) are proposed. With this strategy it is possible to navigate BepiColombo safely through the weak-stability boundary of Mercury and to reach the target periherm with a precision of 11 km.     

Drag balance Cubesat attitude motion effects on in-situ thermosphere density measurements

The dynamics of Cubesats carrying a drag balance instrument (DBI) for in situ atmosphere density measurements is analyzed. Atmospheric drag force is measured by the displacement of two light plates exposed to the incoming particle flow. This system is well suited for a distributed sensor network in orbit, to get simultaneous in situ local (non orbit averaged) measurements in multiple positions and orbit heights, contributing to the development and validation of global atmosphere models. The implementation of the DBI leads to orbit normal pointing spinning two body system. The use of a spin-magnetic attitude control system is suggested, based only on magnetometer readings, contributing to making the system simple, inexpensive, and reliable. It is shown, by an averaging technique, that this system provides for orbit normal spin axis pointing. The effect of the coupling between the attitude dynamics and the DBI is evaluated, analyzing its frequency content and showing that no frequency components arise, affecting the DBI performance. The analysis is confirmed by Monte Carlo numerical simulation results.     

月球轨道编队超长波天文观测微卫星任务

月球背面能够有效屏蔽来自地球并同时遮挡来自太阳的射电信号干扰,拥有太阳系中近乎最安静的电磁环境,是开展空间超长波天文观测的最佳选择区域。在立足完成空间干涉实验的基本任务目标基础、并力争实现重大科学发现的研究思路基础上,研制并发射两颗微卫星,搭载"嫦娥4号"任务进入地月转移轨道,自主完成地月转移、近月制动,在有效燃料约束下形成环月大椭圆轨道编队,构建环月超长波天文干涉仪。说明了系统的工作模式,对数据处理与科学分析方法进行了论述,包括数据预处理、干涉成像与全天功率谱获取角度,进而从支持服务模块和科学载荷模型两个方面对微卫星方案进行了简要概述,凝练了项目任务解决的关键科学与技术问题。月球轨道编队超长波天文观测微卫星的实施将通过全球首个绕月近距编队飞行系统,构建全球首个星–星干涉射电天文观测系统,进而打开人类认识宇宙的新窗口。     

MISTRAM系统定轨的数学方法

通过对ＭＩＳＴＲＡＭ系统跟踪航天飞行器定轨原理的细致的数学分析,得到了一种解算轨道的新方法。该方法不需要标称轨道,计算极为简便,而且精度高;同时还给出了误差传递方式。实测数据和大量模拟计算均表明,该方法有很好的效果。