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251.
S.C. Gallagher W.N. Brandt G. Chartas G.P. Garmire R.M. Sambruna 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2594-2598
Energetic outflows appear to occur in conjunction with active mass accretion onto supermassive black holes. These outflows are most readily observed in the 10% of quasars with broad absorption lines, where the observer’s line of sight passes through the wind. Until fairly recently, the paucity of X-ray data from these objects was notable, but now sensitive hard-band missions such as Chandra and XMM-Newton are routinely detecting broad absorption line quasars. The X-ray regime offers qualitatively new information for the understanding of these objects, and these new results must be taken into account in theoretical modeling of quasar winds. 相似文献
252.
M. Coleman Miller 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2680-2683
Kilohertz QPOs have been detected from more than 20 neutron stars in low-mass X-ray binaries. Several different ideas have been proposed for their generation, involving resonances, magnetic interactions, and sharp transitions in the accretion flow. We show that although details are uncertain at this time, it is clear that the stellar magnetic field has a dynamic influence on the accretion flow. We also discuss the inferences about dense matter and strong gravity that can be drawn from all models, and the qualitative advances expected with a future X-ray timing mission. 相似文献
253.
254.
基于UKF和信息融合的航天器自主导航方法 总被引:1,自引:0,他引:1
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%。 相似文献
255.
物质对X射线的吸收系数和散射系数的计算 总被引:2,自引:0,他引:2
介绍了物质对X射线的光电吸收系数和康普顿散射系数的计算方法。作为算例,在约1keV~1MeV的X射线能量范围内,计算了聚四氟乙烯、某双基推进剂和人体鲜骨对X射线的光电吸收系数和康普顿散射系数。 相似文献
256.
针对能量色散X荧光(Energy dispersive X-ray fluorescence,EDXRF)分析技术应用于煤炭中硫分快速测量过程中存在的基体效应和边缘效应干扰问题,采用蒙特卡罗计算程序Electron-Gamma Shower(EGS)模拟了在不同管电压、不同样品直径、厚度以及不同硫元素浓度条件下的X荧光强度。结果表明,合适的X光管的管电压为15 kV,样
品的临界直径和厚度分别大于1.04 cm和0.05 cm。根据模拟结果,通过实验得到X荧光强度与硫元素浓度的关系曲线,实验结果经过探测效率修正后与EGS模拟结果符合良好,为后续的煤炭中硫分在线快速分析系统的设计和实施提供了有力的技术支撑。 相似文献
257.
Konrad Dennerl 《Space Science Reviews》2006,126(1-4):403-433
X-rays from Mars were first detected in July 2001 with the satellite Chandra. The main source of this radiation was fluorescent
scattering of solar X-rays in its upper atmosphere. In addition, the presence of an extended X-ray halo was indicated, probably
resulting from charge exchange interactions between highly charged heavy ions in the solar wind and neutrals in the Martian
exosphere. The statistical significance of the X-ray halo, however, was very low. In November 2003, Mars was observed again
in X-rays, this time with the satellite XMM-Newton. This observation, characterized by a considerably higher sensitivity,
confirmed the presence of the X-ray halo and proved that charge exchange is indeed the origin of the emission. This was the
first definite detection of charge exchange induced X-ray emission from the exosphere of another planet. Previously, this
kind of emission had been detected from comets (which are largely exospheres) and from the terrestrial exosphere. Because
charge exchange interactions between atmospheric constituents and solar wind ions are considered as an important nonthermal
escape mechanism, probably responsible for a significant loss of the Martian atmosphere, X-ray observations may lead to a
better understanding of the present state of the Martian atmosphere and its evolution. X-ray images of the Martian exosphere
in specific emission lines exhibited a highly anisotropic morphology, varying with individual ions and ionization states.
With its capability to trace the X-ray emission out to at least 8 Mars radii, XMM-Newton can explore exospheric regions far
beyond those that have been observationally explored to date. Thus, X-ray observations provide a novel method for studying
processes in the Martian exosphere on a global scale. 相似文献
258.
Alan M. Levine Hale Bradt Edward H. Morgan Ron Remillard The MIT/GSFC ASM Team 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2970-2975
Selected results from the Rossi X-ray Timing Explorer All-Sky Monitor are presented to illustrate the phenomenology of the light curves. The sensitivity to periodic intensity variations is indicated by the folded light curve of AM Her. The gray line between transient and persistent sources is emphasized. Light curves of a range of systems comprising black holes or neutron stars and low and high mass companion stars show that the behavior of these systems is often, but not always, characteristic. 相似文献
259.
Marina M. Romanova Akshay Kulkarni Min Long Richard V.E. Lovelace Justin V. Wick Galina V. Ustyugova Alexander V. Koldoba 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2887-2892
We performed 2D and full 3D magnetohydrodynamic simulations of disk accretion to a rotating star with an aligned or misaligned dipole magnetic field. We investigated the rotational equilibrium state and derived from simulations the ratio between two main frequencies: the spin frequency of the star and the orbital frequency at the inner radius of the disk. In 3D simulations we observed different features related to the non-axisymmetry of the magnetospheric flow. These features may be responsible for high-frequency quasi-periodic oscillations (QPOs). Variability at much lower frequencies may be connected with restructuring of the magnetic flux threading the inner regions of the disk. Such variability is specifically strong at the propeller stage of evolution. 相似文献
260.
A.M. Soltan M.J. Freyberg 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2535-2539
The X-ray background intensity around galaxies and rich clusters of galaxies is investigated in three energy bands using the ROSAT All-Sky Survey maps. It is found that an amplitude of the XRB enhancements surrounding the Abell clusters and high density areas in the Lick galaxy counts depends on photon energy. Excess flux generated in the surrounding of the galaxy concentrations is consistent with the thermal emission by hot gas postulated by hydrodynamic simulations. 相似文献