超新星遗迹和脉冲星风云的X射线偏振成像

年轻超新星遗迹和脉冲星风云中的高能粒子可以通过同步辐射产生X射线。对该辐射的偏振测量有助于揭示粒子加速区磁场的性质,进而研究粒子加速的机制。首颗X射线偏振成像卫星于2021年底发射升空,已揭示了数个年轻超新星遗迹和脉冲星风云的X射线偏振图像。观测显示,仙后A和第谷超新星遗迹的偏振度较低,平均值分别约为2.5%和9%;而蟹状星云和船帆脉冲星风云的偏振度较高,平均值分别约为20%和45%。结果表明脉冲星风云的磁场较为有序,而两个年轻超新星遗迹的粒子加速区磁场是高度湍动的,且激波附近的磁场结构呈现径向分布。未来,随着对IXPE的使用越来越广泛,以及与我国建设中的增强型X射线时变与偏振探测器(eXTP)等更多望远镜投入使用,以上两类天体的磁场构型和粒子加速模型将得到进一步的限定。

Denoising of X-ray pulsar observed profile using biorthogonal lifting wavelet transform

In X-ray pulsar-based navigation, strong X-ray background noise leads to a low signal-to-noise ratio（SNR） of the observed profile, which consequently makes it very difficult to obtain an accurate pulse phase that directly determines the navigation precision. This signifies the necessity of denoising of the observed profile. Considering that the ultimate goal of denoising is to enhance the pulse phase estimation, a profile denoising algorithm is proposed by fusing the biorthogonal lifting wavelet transform of the linear phase characteristic with the thresholding technique. The statistical properties of X-ray background noise after epoch folding are studied. Then a wavelet-scale dependent threshold is introduced to overcome correlations between wavelet coefficients. Moreover, a modified hyperbola shrinking function is presented to remove the impulsive oscillations of the observed profile. The results of numerical simulations and real data experiments indicate that the proposed method can effectively improve SNR of the observed profile and pulse phase estimation accuracy, especially in short observation durations. And it also outperforms the Donoho thresholding strategy normally used in combination with the orthogonal discrete wavelet transform.

Suzaku observation of Be / X-ray binary pulsar EXO 2030+375

We study the timing and spectral properties of Be/X-ray binary pulsar EXO 2030＋375 using a Suzaku observation taken on 2012 May 23, during a less intense Type I outburst. Pulsations were clearly detected in the X-ray light curves at a barycentric period of 41.2852 s, which suggest that the pulsar is spinning-up. The pulse profiles were found to be peculiar, e.g. unlike those obtained from the earlier Suzaku observation acquired on 2007 May 14. A single-peaked narrow profile at soft X-rays （0.5-10 keV range） changed to a double-peaked broad profile in the 12-55 keV energy range and again reverted back to a smooth single-peaked profile at hard X-rays （55-70 keV range）. The 1.0-100.0 keV broadband spectrum of the pulsar was found to be well described by three continuum models described as （i） a partial covering high energy cut-off power-law model, （ii） a partially absorbed power-law with high- energy exponential rolloff and （iii） a partial covering Negative and Positive power law with EXponential （NPEX） continuum model. Unlike the earlier Suzaku observation during which several low energy emission lines were detected, a weak and narrow Iron Ka emission line at 6.4 keV was only present in the pulsar spectrum during the 2012 May outburst. Non-detection of any absorption like feature in the 1-100 keV energy range supports the claim of the absence of the cyclotron resonance scattering feature in EXO 2030＋375 from the earlier Suzaku observation. Pulse-phase resolved spectroscopy revealed the presence of additional dense matter causing the absence of a second peak from the soft X-ray pulse profiles. The details of the results are described in the paper.

一种快速X射线脉冲星光子到达时间转换的简化模型

高精度X射线光子到达时间转换模型对脉冲星导航的精度至关重要,针对目前完整模型复杂而简化模型精度有限的问题,本文提出了一种精度不低于已有简化模型的快速简化模型.通过对现有完整模型的推导,从理论上分析了各延迟项对模型精度的影响,指出罗曼延迟仍是影响简化模型精度的关键.通过改变罗曼延迟的表达式及其二阶展开方式并考虑物理量的易获取度,得到一种快速简化模型.利用完整模型及所提简化模型对中子星内部组成探测器(Neutron star Interior Composition Explorer,NICER)和慧眼硬X射线调制望远镜(Hard X-ray Modulation Telescope,HXMT)的实测光子数据进行时间转换,分析了所提模型的精度和计算效率;利用数值仿真分析了轨道高度、脉冲星角位置测量误差对简化模型精度的影响,讨论了不同高度地球轨道应用中该简化模型的精度及计算效率.结果表明本文所提简化模型相比Sheikh简化模型和fei模型计算效率分别提高50%和10%,且未造成精度降低.

AstroSat observation of the Be/X-ray binary Pulsar 3A 0726–260(4U 0728–25)

Results on timing and spectral properties of the Be/X-ray binary pulsar 3A 0726-260(4U 0728-25)are presented.The binary was observed on 2016 May 6-7 with the Large Area X-ray Proportional Counter(LAXPC)and Soft X-ray Telescope(SXT)instruments onboard the AstroSat satellite.During this observation,the source was in non-flaring persistent state at a flux level of^8.6±0.3×10^-11 erg cm^-2 s^-1in 0.4-20 keV.Strong X-ray pulsations with a period of 103.144±0.001 s are detected in 0.3-7 keV with the SXT and in 3-40 keV with the LAXPC.The pulse profile is energy dependent,and there is an indication that the pulse shape changes from a broad single pulse to a double pulse at higher energy.At energies above20 keV,we report the first time detection of pulsation period 103.145±0.001 s and the double peaked pulse profile from the source.The energy spectrum of the source is derived from the combined analysis of the SXT and LAXPC spectral data in 0.4-20 keV.The best spectral fit is obtained by a power law model with a photon index(1.7±0.03)with high energy spectral cut-off at 12.9±0.7 keV.A broad iron line at^6.3 keV is detected in the energy spectrum.We briefly discuss the implications of these results.

Modification of gravitational redshift of x-ray burst produced by pulsar surface magnetoplasma

In this paper, the propagation of x-ray bursts in the magnetoplasma of pulsar magnetosphere is discussed. The electromagnetic interaction between x-ray bursts and magnetoplasma is described as some geometry. The electromagnetic effects of surface superstrong magnetic field and dynamic effects of outflowing magnetoplasma of pulsars are treated as an optical metric. The Gordon metric is introduced to represent the gravitational metric and optical metric. So the propagation of x-ray bursts in magnetoplasma of pulsars can be described as x-ray bursts transmitting in an effective space characterized by Gordon metric. The modification of gravitational redshift, attributed to the flowing magnetoplasma of pulsars, is obtained and it is shown that the modification is of redshift and can reach the same magnitude as the gravitational redshift for ordinary pulsars.

Detectability of rotation-powered pulsars in future hard X-ray surveys

Recent INTEGRAL/IBIS hard X-ray surveys have detected about 10 young pulsars. We show hard X-ray properties of these 10 young pulsars, which have a luminosity of 10^33 - 10^37 erg s^-1 and a photon index of 1.6-2.1 in the energy range of 20-100 keV. The correlation between X-ray luminosity and spin-down power of Lx ∝ Lsd^1.31 suggests that the hard X-ray emission in rotation-powered pulsars is dominated by the pulsar wind nebula （PWN） component. Assuming spectral properties are similar in 20-100keV and 2-10 keV for both the pulsar and PWN components, the hard X-ray luminosity and flux of 39 known young X-ray pulsars and 8 millisecond pulsars are obtained, and a correlation of Lx ∝ Lsd^1.5 is derived. About 20 known young X-ray pulsars and 1 millisecond pulsars could be detected with future INTEGRAL and HXMT surveys. We also carry out Monte Carlo simulations of hard X-ray pulsars in the Galaxy and the Gould Belt, assuming values for the pulsar birth rate, initial position, proper motion velocity, period, and magnetic field distribution and evolution based on observational statistics and the Lx - Lsd reltions：Lx ∝Lsd^1.31 and Lx∝Lsd^1.5 More than 40 young pulsars （mostly in the Galactic plane） could be detected after ten years of INTEGRAL surveys and the launch of HXMT. So, the young pulsars would be a significant part of the hard X-ray source population in the sky, and will contribute to unidentified hard X-ray sources in present and future hard X-ray surveys by INTEGRAL and HXMT.

Spectral Properties of Anomalous X-ray Pulsars

We examine the spectra of the persistent emission from anomalous X-ray pulsars (AXPs) and their variation with the spin-down rate . Based on an accretion-powered model, the influences of both the magnetic field and the mass accretion rate on the spectral properties of AXPs are addressed. We then investigate the relation between the spectral property of AXPs and mass accretion rate . The result shows that there exists a linear correlation between the photon index and the mass accretion rate: the spectral hardness increases with increasing . A possible emission mechanism for the explanation of the spectral properties of AXPs is also discussed.

A Two-Temperature Supernova Fallback Disk Model for Anomalous X-ray Pulsars

We present a case study of the relevance of the radially pulsational instability of a two-temperature accretion disk around a neutron star to anomalous X-ray pulsars (AXPs). Our estimates are based on the approximation that such a neutron star disk with mass in the range of 10-6-10-5 M⊙ is formed by supernova fallback. We derive several peculiar properties of the accretion disk instability: a narrow interval of X-ray pulse periods; lower X-ray luminosities; a period derivative and an evolution time scale. All these results are in good agreement with the observations of the AXPs.

Understanding the X-ray spectrum of anomalous X-ray pulsars and soft gamma-ray repeaters

Hard X-rays above 10 keV are detected from several anomalous X-ray pul- sars （AXPs） and soft gamma-ray repeaters （SGRs）, and different models have been proposed to explain the physical origin within the frame of either a magnetar model or a fallback disk system. Using data from Suzaku and INTEGRAL, we study the soft and hard X-ray spectra of four AXPs/SGRs： 1RXS J 170849-400910, 1E 1547.0- 5408, SGR 1806-20 and SGR 0501＋4516. It is found that the spectra could be well reproduced by the bulk-motion Comptonization （BMC） process as was first suggested by Triimper et al., showing that the accretion scenario could be compatible with X- ray emission from AXPs/SGRs. Simulated results from the Hard X-ray Modulation Telescope using the BMC model show that the spectra would have discrepancies from the power-law, especially the cutoff at -200 keV. Thus future observations will allow researchers to distinguish different models of the hard X-ray emission and will help us understand the nature of AXPs/SGRs.

Broad-band spectroscopy of the transient X-ray binary pulsar KS 1947+300 during 2013 giant outburst: Detection of pulsating soft X-ray excess component

We present the results obtained from detailed timing and spectral studies of the Be/X-ray binary pulsar KS 1947＋300 during its 2013 giant outburst. We used data from Suzaku observations of the pulsar at two epochs, i.e. on 2013 October 22 （close to the peak of the outburst） and 2013 November 22. X- ray pulsations at - 18.81 s were clearly detected in the light curves obtained from both observations. Pulse periods estimated during the outburst showed that the pulsar was spinning up. The pulse profile was found to be single-peaked up to -10 keV beyond which a sharp peak followed by a dip-like feature appeared at hard X-rays. The dip-like feature has been observed up to -70 keV. The 1-110 keV broad-band spectroscopy of both observations revealed that the best-fit model was comprised of a partially absorbed Negative and Positive power law with EXponential cutoff （NPEX） continuum model along with a blackbody component for the soft X-ray excess and two Gaussian functions at 6.4 and 6.7 keV for emission lines. Both the lines were identified as emission from neutral and He-like iron atoms. To fit the spectra, we included the previously reported cyclotron absorption line at 12.2 keV. From the spin-up rate, the magnetic field of the pulsar was estimated to be -1.2 x 10^12 G and found to be comparable to that obtained from the detection of the cyclotron absorption feature. Pulse-phase resolved spectroscopy revealed the pulsating nature of the soft X-ray excess component in phase with the continuum flux. This confirms that the accretion column and/or accretion stream are the most probable regions of the soft X-ray excess emission in KS1947＋300. The presence of the pulsating soft X-ray excess in phase with continuum emission may be the possible reason for not observing the dip at soft X-rays.

In-Orbit Calibration and Data Analysis of China＇s First Grazing Incidence Focusing X-Ray Pulsar Telescope

The grazing incidence focusing X-ray pulsar telescope(iFXPT), as the main payload of the X-ray Pulsar Navigation Test Satellite(XPNAV-1), will have great significance on China's space scientific exploration and X-ray pulsar navigation. With PSR B0531+21(Crab Pulsar) as the observation target, the pulsar profile has been recovered based on the data obtained by iFXPT, realizing the main objective of "observing" PSR B0531+21 for the first time in China. This payload mainly consists of the Wolter-I X-ray optics, silicon drift detector, magnetic deflector, electronics, high-energy particle shield and high-stability structures. Currently, the iFXPT, with its good in-orbit performance, has obtained a considerable observation data. The effective area, sensitivity and energy response have been calibrated both on ground and in-orbit, demonstrating a high degree of consistency. Meanwhile, the in-orbit observation data and information for pulsar navigation has also been analyzed simultaneously. As a result, the feasibility of the exploration scheme and the performance of the telescope have been fully validated.

X射线脉冲星计时导航应用模式与空间试验进展

结合国家导航体系发展与工程应用迫切需求,主要讨论了X射线脉冲星计时导航的应用模式,并介绍了国内外空间试验进展。总结了脉冲星计时地基射电与空间X射线观测的特点和发展现状,阐释了脉冲星时研究与发展的重要意义;总结并归纳了X射线脉冲星导航的应用特点和现有水平,讨论了X射线脉冲星导航的技术优势和典型应用场景;总结了国内外X射线脉冲星计时导航的空间试验进展。根据国内外的空间试验结果,脉冲星时稳定度可达10^(-14)量级,脉冲星导航精度可达到km量级,初步具备在轨应用价值。因此,加快推进国内脉冲星计时导航技术的在轨演示验证与工程应用具有重要意义。

STUDY ON WOOD COMPOSITES DENSITY UNIFORMITY BY X-RAY

X-ray is irradiated in some wood composites(multi-layer particleboard.sin-gle-layer particleboard,reconsolidated wood,).According to the gray degree principle(0-255 grade degree)and the corresponding relation between density and gray,X-raynegatives are scanned.The numbers and pictures of every degree density are obtained andaccurate composite densities are counted.

XPNAV-1和NICER对Crab脉冲星观测数据的比较分析

通过对比NICER(Neutron Star Interior Composition Explorer)和XPNAV-1(X-ray Pulsar Navigation-1)关于Crab脉冲星同一时段(108天)观测数据的计时处理结果,发现在周期跃变发生前的时段(95天),NICER数据的拟合前计时残差的RMS(root mean square)为5.77μs,远优于XPNAV-1数据的拟合前计时残差的RMS 51.56μs,体现了NICER在有效面积、探测效率、数据采集等方面的优势,给未来我国的X射线脉冲星探测器研制提供了发展方向;而在周期跃变发生后的时段(13天),发现XPNAV-1数据的拟合前计时残差的RMS为55.87μs,而NICER数据的拟合前计时残差的RMS为167.27μs,周期跃变对NICER的影响更大,说明在处理周期跃变发生后时段的NICER数据时,由于NICER的观测精度非常高,需要更频繁地更新Crab星历。最后分别得到了两个探测器整段数据的计时残差。XPNAV-1数据的拟合前计时残差的RMS为55.94μs,而NICER数据的拟合前计时残差的RMS为64.34μs,这说明NICER数据受周期跃变影响更为明显,进一步证明了上述结论。

Variations in the X-ray eclipse transitions of Cen X-3

We report here an investigation of the X-ray eclipse transitions of the high mass X-ray binary pulsar Cen X-3 in different intensity states. The long term light curve of Cen X-3 obtained with RXTE-ASM spanning more than 5000 d shows strong aperiodic flux variations with low and high states. We have investigated the eclipse transitions of Cen X-3 in different intensity states with data obtained from pointed observations with the more sensitive instruments onboard ASCA, BeppoSAX, XMM- Newton, Chandra and RXTE. We found a very clear trend of sharp eclipse transitions in the high state and longer transitions in the low state. This is a confirmation of this feature first observed with the RXTE-ASM but now observed with much better clarity. From the light curves obtained from several missions, it is seen that the eclipse egress in the low state starts earlier by an orbital phase of 0.02 compared to the eclipse egress in the high state indicating that the observed X-rays originate from a much larger region. We have also performed spectral analysis of the post-eclipse part of each observation. From BeppoSAX observations, the out-of-eclipse X-ray flux is found to differ by a factor of -26 during the high and low intensity states while the eclipse count rates differ by a factor of only ~ 4.7. This indicates that in the low state, there is an additional scattering medium which scatters some of the source photons towards the observer even when the neutron star is completely eclipsed. We could also resolve the three iron line components using XMM-Newton observation in the low state. By comparing the iron line equivalent width during the high and low states, it is seen that the width of the iron line is relatively large during the low state which supports the fact that significant reprocessing and scattering of X-rays takes place in the low state.

Variations of the harmonic components of the X-ray pulse profile of PSR B1509–58

We used the Fourier decomposition technique to investigate the stability of the X-ray pulse profile of a young pulsar PSR B1509–58 by studying the relative amplitudes and phase differences of its harmonic components with respect to the fundamental using data from the Rossi X-Ray Timing Explorer. Like most young rotation powered pulsars, PSR B1509–58 has a high spin down rate. It also has less timing noise, allowing accurate measurement of higher order frequency derivatives which in turn helps in the study of the physics of pulsar spin down. Detailed investigation of pulse profiles over the years will help us establish any possible connection between the timing characteristics and the high energy emission characteristics for this pulsar.Furthermore, the study of pulse profiles of short period X-ray pulsars can also be useful when used as a means of interplanetary navigation. The X-ray pulse profile of this source has been analyzed for 15 yr（1996–2011）. The long term average amplitudes of the first, second and third harmonics（and their standard deviation for individual measurements） compared to the fundamental are 36.9%（1.7%）, 13.4%（1.9%） and 9.4%（1.8%） respectively. Similarly, the phases of the three harmonics（and standard deviations） with respect to the fundamental are 0.36（0.06）, 1.5（0.2） and 2.5（0.3） radian respectively. We do not find any significant variation of the harmonic components of the pulse profile in comparison to the fundamental.

X射线脉冲星导航原理

X射线脉冲星导航是以脉冲星的X射线辐射信号作为信息输入,经过相应的信号和数据处理,为近地轨道、深空和星际空间飞行的航天器提供高精度的位置、速度、时间和姿态等导航信息的实现过程。首先提出了基于X射线脉冲星的卫星自主导航的基本框架和实现流程;然后,概述X射线脉冲导航的时空基准,重点研究X射线脉冲星导航定位的测量方程、系统状态方程及其噪声统计特征等数学模型。最后,详细论述卫星自主导航信息处理的鲁棒滤波算法,即经典算法和现代鲁棒滤波算法。从理论方法和工程应用角度,初步论证X射线脉冲星导航的原理可行性和算法可实现性。

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．

X射线脉冲星导航测量延时补偿方法研究

X射线脉冲光子是脉冲星导航系统原始观测量,利用脉冲叠加技术获取的脉冲星观测量存在测量延时问题。通过分析脉冲叠加技术原理,将脉冲星导航系统测量延时问题转化为对光子延迟时间序列的研究。提出基于轨道外推的延时补偿方法和基于组合导航的延时补偿方法,前者计算量小,宜于在测量延时较小时使用,后者不受延时大小的限制。最后通过数学仿真验证了所提方法的有效性。