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A super-high angular resolution principle for coded-mask X-ray imaging beyond the diffraction limit of a single pinhole

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Chinese Journal of Astronomy and Astrophysics 2009年第3期9卷 333-340页

作者： Chen zhang shuang-nan zhang Department of Engineering Physics ＆ Center for Astrophysics Tsinghua University Beijing 100084 China Key Labora.tory of Particle Astrophysics Institute of High Energy Physics the Chinese Academy of Sciences Beijing 100049 China Department of Physics ＆ Center for Astrophysics Tsinghua University Beijing 100084 China

High angular resolution X-ray imaging is always useful in astrophysics and solar physics. In principle, it can be performed by using coded-mask imaging with a very long mask-detector distance. Previously, the diffraction-interference effect was thought to degrade coded-mask imaging performance dramatically at the low energy end with its very long mask-detector distance. The diffraction-interference effect is described with numerical calculations, and the diffraction-interference cross correlation reconstruction method （DICC） is developed in order to overcome the imaging performance degradation. Based on the DICC, a super-high angular resolution principle （SHARP） for coded-mask X-ray imaging is proposed. The feasibility of coded mask imaging beyond the diffraction limit of a single pinhole is demonstrated with simulations. With the specification that the mask element size is 50 × 50 μm^2 and the mask-detector distance is 50 m, the achieved angular resolution is 0.32arcsec above about 10keV and 0.36arcsec at 1.24keV （λ = 1 nm）, where diffraction cannot be neglected. The on-axis source location accuracy is better than 0.02 arcsec. Potential applications for solar observations and wide-field X-ray monitors are also briefly discussed.

关键词： instrumentation high angular resolution - techniques image processing - telescopes

Development of the super high angular resolution principle for X-ray imaging

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Research in Astronomy and Astrophysics 2011年第1期11卷 119-124页

作者： Chen zhang shuang-nan zhang National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China Department of Physics ＆ Center for Astrophysics Tsinghua University Beijing 100084 China Key Laboratory of Particle Astrophysics Institute of High Energy Physics Chinese Academy ofSciences Beijing 100049 China

Development of the Super High Angular Resolution Principle （SHARP） for coded-mask X-ray imaging is presented. We prove that SHARP can be considered as a generalized coded mask imaging method with a coding pattern comprised of diffraction-interference fringes in the mask pattern. The angular resolution of SHARP can be improved by detecting the fringes more precisely than the mask＇s element size, i.e. by using a detector with a pixel size smaller than the mask＇s element size. The proposed mission SHARP-X for solar X-ray observations is also briefly discussed.

关键词： instrumentation: high angularresolution-- techniques: image processing-- telescopes

Detecting super-Nyquist-frequency gravitational waves using a pulsar timing array

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Science China(Physics,Mechanics & Astronomy) 2016年第8期59卷 78-86页

作者： Shu-Xu Yi shuang-nan zhang Key Laboratory of Particle Astrophysics Institute of High Energy Physics Chinese Academy of Sciences Beijing 100049 China University of Chinese Academy of Sciences Beijing 100049 China Space Science Division National Astronomical Observatories of China Chinese Academy of Sciences Beijing 100012 China

The maximum frequency of gravitational waves(GWs) detectable with traditional pulsar timing methods is set by the Nyquist frequency( fNy) of the observation. Beyond this frequency, GWs leave no temporal-correlated signals; instead, they appear as white noise in the timing residuals. The variance of the GW-induced white noise is a function of the position of the pulsars relative to the GW source. By observing this unique functional form in the timing data, we propose that we can detect GWs of frequency >f_(Ny)(super-Nyquist frequency GWs; SNFGWs). We demonstrate the feasibility of the proposed method with simulated timing *** a selected dataset from the Parkes Pulsar Timing Array data release 1 and the North American nanohertz Observatory for Gravitational Waves publicly available datasets, we try to detect the signals from single SNFGW sources. The result is consistent with no GW detection with 65.5% probability. An all-sky map of the sensitivity of the selected pulsar timing array to single SNFGW sources is generated, and the position of the GW source where the selected pulsar timing array is most sensitive to is λ_s =.0.82,β_s =-1.03(rad); the corresponding minimum GW strain is h = 6.31 × 10^(-11) at f = 1 × 10^(-5) Hz.

关键词： gravitational wave pulsar black hole

Comparison between Windowed FFT and Hilbert-Huang Transform for Analyzing Time Series with Poissonian Fluctuations: A Case Study

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Chinese Journal of Astronomy and Astrophysics 2006年第4期6卷 503-512页

作者： Dong Han shuang-nan zhang Department of Engineering Physics ＆ Center for Astrophysics Tsinghua University Beijing 100084 Department of Physics ＆ Center for Astrophysics Tsinghua University Beijing 100084 Key Laboratory of Particle Astrophysics Institute of High Energy Physics Chinese Academy of Sciences Beijing 100049

Hilbert-Huang Transform （HHT） is a novel data analysis technique for nonlinear and non-stationary data. We present a time-frequency analysis of both simulated fight curves and an X-ray burst from the X-ray burster 4U 1702-429 with both the HHT and the Windowed Fast Fourier Transform （WFFT） methods. Our results show that the HHT method has failed in all cases for light curves with Poissonian fluctuations which axe typical for all photon counting instruments used in astronomy, whereas the WFFT method can sensitively detect the periodic signals in the presence of Poissonian fluctuations; the only drawback of the WFFT method is that it cannot detect sharp frequency variations accurately.

关键词： methods: data analysis -- stars: oscillations (including pulsations) -- X-rays:bursts

Cross-Correlation Detection of Point Sources in the WMAP First Year Data

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Chinese Journal of Astronomy and Astrophysics 2007年第2期7卷 199-208页

作者： Jian-Yin Nie shuang-nan zhang Department of Physics and Center for Astrophysics Tsinghua University Beijing 100084 Key Laboratory of Particle Astrophysics Institute of High Energy Physics Chinese Academy ofSciences Beijing 100049

We apply a Cross-Correlation （CC） method developed previously for detecting gamma-ray point sources to the WMAP first year data by using the Point-Spread Function of WMAP and obtain a full sky CC coefficient map. We find that the CC method is a powerful tool to examine the WMAP foreground residuals which can be further cleaned accord- ingly. Evident foreground signals are found in the WMAP foreground cleaned maps and the Tegmark cleaned map. In this process 101 point sources are detected, and 26 of them are new sources additional to the originally listed WMAP 208 sources. We estimate the flux of these new sources and verify them by another method. As a result, a revised mask file based on the WMAP first year data is produced by including these new sources.

关键词： cosmic microwave background: WMAP - cross-correlation - radio point source

Modeling the evolution and distribution of the frequency's second derivative and the braking index of pulsar spin

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Research in Astronomy and Astrophysics 2015年第7期15卷 963-974页

作者： Yi Xie shuang-nan zhang Jin-Yuan Liao National Astronomical Observatories Chinese Academy of Sciences University of Chinese Academy of Sciences Key Laboratory of Particle Astrophysics Institute of High Energy Physics Chinese Academy of Sciences Physics Department University of Alabama in Huntsville

We model the evolution of the spin frequency＇s second derivative ν¨ and the braking index n of radio pulsars with simulations within the phenomenological model of their surface magnetic field evolution, which contains a long-term power-law decay modulated by short-term oscillations. For the pulsar PSR B0329＋54, a model with three oscillation components can reproduce its ν¨ variation. We show that the ＂averaged＂ n is different from the instantaneous n, and its oscillation magnitude decreases abruptly as the time span increases, due to the ＂averaging＂ effect. The simulated timing residuals agree with the main features of the reported data. Our model predicts that the averaged ν¨ of PSR B0329＋54 will start to decrease rapidly with newer data beyond those used in Hobbs et al. We further perform Monte Carlo simulations for the distribution of the reported data in ｜ν¨｜ and ｜n｜ versus characteristic age τ*** is found that the magnetic field oscillation model with decay index α = 0 can reproduce the distributions quite well. Compared with magnetic field decay due to the ambipolar diffusion（α = 0.5） and the Hall cascade（α = 1.0）, the model with no long term decay（α = 0） is clearly preferred for old pulsars by the p-values of the two-dimensional Kolmogorov-Smirnov test.

关键词： stars: neutron -- pulsars: individual (B0329+54) -- pulsars: general --magnetic fields

A possible origin of the Galactic Center magnetar SGR 1745–2900

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Research in Astronomy and Astrophysics 2017年第6期17卷 47-54页

作者： Quan Cheng shuang-nan zhang Xiao-Ping Zheng Key Laboratory of Particle Astrophysics Institute of High Energy PhysicsChinese Academy of Sciences Institute of Astrophysics Central China Normal University

Since there is a large population of massive O/B stars and putative neutron stars （NSs） located in the vicinity of the Galactic Center （GC）, intermediate-mass X-ray binaries （IMXBs） constituted by an NS and a B-type star probably exist there. We investigate the evolutions of accreting NSs in IMXBs （similar to M82 X-2） with a - 5.2 M companion and orbital period 2.53 d. By adopting a mildly super-Eddington rate M = 6 × 10-8 M yr-1 for the early Case B Roche-lobe overflow （RLOF） accretion, we find that only in accreting NSs with quite elastic crusts （slippage factor s = 0.05） can the toroidal magnetic fields be amplified within 1 Myr, which is assumed to be the longest duration of the RLOF. These IMXBs will evolve into NS＋white dwarf （WD） binaries if they are dynamically stable. However, before the formation of NS＋WD binaries, the high stellar density in the GC will probably lead to frequent encounters between the NS＋evolved star binaries （in post-early Case B mass transfer phase） and NSs or exchange encounters with other stars, which may produce single NSs. These NSs will evolve into magnetars when the amplified poloidal magnetic fields diffuse out to the NS surfaces. Consequently, our results provide a possible expianation for the origin of the GC magnetar SGR 1745-2900. Moreover, the accreting NSs with s 〉 0.05 will evolve into millisecond pulsars （MSPs）. Therefore, our model reveals that the GC magnetars and MSPs could both originate from a special kind of IMXB.

关键词： stars neutron - stars magnetars - stars magnetic field - pulsars individual (SGR1745-2900)

An unusual timing and spectral state of a black hole microquasar XTE J1550-564

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Chinese Journal of Astronomy and Astrophysics 2009年第2期9卷 179-190页

作者： Ying-Kang Jin shuang-nan zhang Ti-Pei Li Department of Engineering Physics and Center for Astrophysics Tsinghua University Beijing 100084 China Department of Physics and Center for Astrophysics Tsinghua University Beijing 100084 China Key Laboratory of Particle Astrophysics Institute of High Energy Physics Chinese Academy of Sciences Beijing 100049 China

An unusual timing and spectral state of a black hole microquasar XTE J1550- 564 observed with RXTE is analyzed. Millisecond variabilities are found, which are significantly shorter than the minimum possible time scale in the light curves of black hole binaries, as suggested by Sunyaev ＆ Revnivtsev （2000）. The X-ray spectral fitting result indicates that there is an unusual soft component in the spectrum, which may be responsible for the millisecond variabilities. The millisecond variabilities as well as the unusual soft spectral component should be produced from some small, but independent active regions in the accretion disk.

关键词： methods data analysis -- X-rays binaries -- X-rays individual (XTEJ1550-564)

Comparisons of Jet Properties between GeV Radio Galaxies and Blazars

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Research in Astronomy and Astrophysics 2017年第9期17卷 15-24页

作者： Zi-Wei Xue Jin zhang Wei Cui En-Wei Liang shuang-nan zhang Key Laboratory of Space Astronomy and Technology National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100012China University of Chinese Academy of Sciences Beijing 100049China Department of Physics and Astronomy Purdue UniversityWest LafayetteIN 47907USA Guangxi Key Laboratory for Relativistic Astrophysics Department of PhysicsGuangxi UniversityNanning 530004China Key Laboratory of Particle Astrophysics Institute of High Energy PhysicsChinese Academy of SciencesBeijing 100049China

We compile a sample of spectral energy distributions （SEDs） of 12 GeV radio galaxies （RGs）, including eight FR I RGs and four FR II RGs. These SEDs can be represented with the one-zone leptonic model. No significant unification, as expected in the unification model, is found for the derived jet parameters between FR I RGs and BL Lacertae objects （BL Lacs） and between FR II RGs and flat spectrum radio quasars （FSRQs）. However, on average FR I RGs have a larger ＇Tb （break Lorentz factor of electrons） and lower B （magnetic field strength） than FR II RGs, analogous to the differences be- tween BL Lacs and FSRQs. The derived Doppler factors （~） of RGs are on average smaller than those of blazars, which is consistent with the unification model such that RGs are the misaligned parent pop- ulations of blazars with smaller tS. On the basis of jet parameters from SED fits, we calculate their jet powers and the powers carded by each component, and compare their jet compositions and radiation efficiencies with blazars. Most of the RG jets may be dominated by particles, like BL Lacs, not FSRQs. However, the jets of RGs with higher radiation efficiencies tend to have higher jet magnetization. A strong anticorrelation between synchrotron peak frequency and jet power is observed for GeV RGs and blazars in both the observer and co-moving frames, indicating that the ＂sequence＂ behavior among blazars, together with the GeV RGs, may be intrinsically dominated by jet power.

关键词： galaxies: active -- galaxies: general -- galaxies jets -- gamma rays galaxies -- radiation mechanisms non-thermal