Measuring the matter distribution within z = 0.2 cluster lenses with XMM-Newton

We present an analysis of seven clusters observed by XMM-Newton as part of our survey of 17 most X-ray luminous clusters of galaxies at z  0.2 selected for a comprehensive and unbiased study of the mass distribution in massive clusters. Using the public software FTOOLS and XMMSAS we have set up an automated pipeline to reduce the EPIC MOS and pn spectro-imaging data, optimized for extended sources analysis. We also developped a code to perform intensive spectral and imaging analysis particularly focussing on proper background estimate and removal. XMM-Newton deep spectro-imaging of these clusters allowed us to fit a standard β-model to their gas emission profiles as well as a standard MEKAL emission model to their extracted spectra, and test their inferred characteristics against already calibrated relations.     

Time-dependent thermal X-ray afterglows from GRBS

Time-dependent thermal X-ray spectra are calculated from physically plausible conditions around GRB. It is shown that account for time-dependent ionization processes strongly affects the observed spectra of hot rarefied plasma. These calculations may provide an alternative explanation to the observed X-ray lines of early GRBs afterglows (such as GRB 011211). Our technique will allow one to obtain independent constraints on the GRB collimation angle and on the clumpiness of circumstellar matter.     

Kilohertz quasi-periodic oscillations in SAX J1808.4–3658

I present a short overview of the behavior and properties of the two simultaneous kilohertz quasi-periodic oscillations (kHz QPOs) seen in the accreting millisecond X-ray pulsar SAX J1808.4–3658. I will focus on the behavior of the upper frequency QPO as a function of time and count rate as seen during the 2002 outburst of this source. I will also discuss briefly the correlated behavior of this QPO with QPOs at lower frequencies (several tens of hertz).     

Appearance of neutron stars in the state of subsonic propeller

The state of subsonic propeller is intermediate between the states of supersonic propeller and accretor in the evolutionary tracks of magnetized compact stars. The rotational rate of a star at this stage decelerates due to the interaction between its magnetosphere and the surrounding hot, quasi-static plasma envelope. The magnetospheric radius is smaller than the corotation radius and the boundary of the magnetosphere is stable with respect to interchange instabilities. The rate of the mass flux from the inner radius of the envelope to the stellar surface is limited by the rate of plasma diffusion into the magnetic field of the star. As a result, the subsonic propeller would appear as a low-luminosity accretion-powered pulsar with a soft X-ray spectrum.     

太阳微波爆发精细结构与硬X射线耀斑的相关

北京天文台在２．８４ＧＨｚ频率上观测到的带短时标精细结构的微波爆发与日本ＹＯＨＫＯＨ卫星上ＨＸＴ在１９９１年１０月－１９９２年１２月观测到的硬Ｘ射线爆发（ＨＸＢ）事件作了比较，发现在２０个微波精细结构爆发事件只有１２个与ＹＯＨＫＯＨ卫星记录的ＨＸＢ有对应关系．本文对１９９２年６月７日典型事件中２．８４ＧＨｚ与ＨＸＢ共同存在的百秒量级的准周期振荡作了分析及源区参数的计算，并作了简要的讨论．     

X-ray synchrotron nebulae and the origin of neutron stars

“With all reserve, we advance the view that a supernova represents the transition of an ordinary star into a neutron star.”This conclusion, reached just 50 years ago in a classic paper by Walter Baade and Fritz Zwicky (1934), was published three decades before the first direct observational evidence for the existence of neutron stars was uncovered. It still informs the standard picture of neutron star production in the Galaxy. We examine herein some recent evidence bearing on this question which has been derived from Observatory X-ray observations of supernova remnants and radio pulsars. In particular, the discovery that X-ray synchrotron nebulae are found surrounding most young ( 10⁶ yr) pulsars observed to date is discussed. We explore the implications of the lack of such nebulae in the majority of supernova remnants (SNR) for the properties and frequency of neutron star formation in supernova events.     

Magnetar spectra and twisted magnetospheres

The huge potential drop between the footpoints of the closed field lines in the twisted magnetospheres of magnetars may accelerate electrons up to very high energies, γ ? 10⁶. On the other hand, the comparison between the observed spectra of magnetars and spectra obtained by accurate theoretical models seems to favor of a picture in which the magnetosphere is filled by “slow” electrons (v ? 0.8c), rather than by ultra-relativistic particles.     

Modeling the broadband persistent emission of magnetars

In this paper, we discuss our first attempts to model the broadband persistent emission of magnetars within a self-consistent, physical scenario. We present the predictions of a synthetic model that we calculated with a new Monte Carlo 3D radiative code. The basic idea is that soft thermal photons (e.g. emitted by the star surface) can experience resonant cyclotron upscattering by a population of relativistic electrons treated in the twisted magnetosphere. Our code is specifically tailored to work in the ultra-magnetized regime; polarization and QED effects are consistently accounted for, as well different configurations for the magnetosphere. We discuss the predicted spectral properties in the 0.1–1000 keV range, the polarization properties, and we present the model application to a sample of magnetars soft X-ray spectra.     

ASTROSAT

The ASTROSAT satellite is an Indian National Space Observatory under development in India. Due for launch in 2010, ASTROSAT will carry a complement of five scientific instruments enabling simultaneous observations from the optical through to the hard X-ray energy band. This capability will enable broad-band spectroscopy and high time-resolution monitoring of both galactic and extra-galactic targets, such as X-ray binaries and AGN. One of the instruments is being built in collaboration with the Canadian Space Agency and another in collaboration with the University of Leicester. ASTROSAT also carries a scanning sky monitor to observe the variable X-ray sky. After an initial period of science verification and guaranteed time, a certain fraction of ASTROSAT observing time will also be made available to the community via a call for proposals. Here I summarise the instrument complement and principle scientific objectives of the mission.     

X射线脉冲星导航硬件脉冲轮廓累积研究

为了在X射线脉冲星地面实验系统仿真源模拟产生X射线的基础上,能够快速稳定地得到脉冲轮廓,采用硬件历元叠加的方法获得脉冲轮廓。研究了用硬件实现历元叠加及其数据整合的算法,该算法首先在MATLAB现场可编程逻辑阵列(FPGA)中实现,再通过MATLAB硬件描述语言(HDL)代码生成模块把算法转换成HDL,经编译后获得配置硬件的Bit文件,最终在开发板FPGA上实现数据处理的硬件模块。一段时间内的光子到达时间数据通过MATLAB算法得到的脉冲轮廓数据与通过硬件模块处理后得到的数据结果存在误差,在单个时间窗口内误差最大值为2个光子数,误差平均值占光子数统计平均值的0.084%;两组统计的脉冲轮廓数据中不同数据占总数据个数的9.481%,这样的误差不影响后端模拟导航模块的导航。利用硬件实现的历元叠加及其数据整合模块具有处理速度快、设备紧凑、功耗低的特点,为航天器利用X射线脉冲星导航提供了一种可行的硬件数据处理技术上的支持。