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Do Globular Clusters Harbor Black Holes?

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chinese Journal of Astronomy and Astrophysics 2001年第4期1卷 291-295页

作者： Xian-Zhong Zheng (national astronomical Observatories, chinese academy of sciences, beijing 100012)E-mail:zxz@*** national astronomical Observatories Chinese Academy of Sciences Beijing 100012

It has been firmly established that there exists a tight correlation be- tween the mass of the central black hole and velocity dispersion (or luminosity) in elliptical galaxies, 'pseudobulges' and bulges of galaxies, although the nature of this correlation still remains nuclear. We explore the possibility of extrapolating such a correlation to less massive, spherical systems like globular clusters. In particular, motivated by the apparent success in the globular cluster M15, we present an estimate of the central black hole mass for a number of globular clusters with available velocity dispersion data.

关键词： black hole physics-globular clusters: general - galaxies: general

A Check on the Cardassian Expansion Model with Type-la Supernovae Data

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chinese Journal of Astronomy and Astrophysics 2003年第4期3卷 341-346页

作者： Li Caonational astronomical Observatories, chinese academy of sciences, beijing 100012

We use the magnitude-redshift relation for the type Ia supernova datacompiled by Riess et al. to analyze the Cardassian expansion scenario. This scenario assumes theuniverse to be flat, matter dominated, and accelerating, but contains no vacuum contribution. Thebest fitting model parameters are H_0 = 65.3 km s^(-1) Mpc^(-1), n = 0.35 and Ω_m = 0.05. When thehighest redshift supernova, SN 1997ck, is excluded, H_0 remains the same, but n becomes 0.20 andΩ_m, 0.15, and the matter density remains unreasonably low. Our result shows that this particularscenario is strongly disfavoured by the SNeIa data.

关键词： supernovae: general cosmology: theory distances and redshifts

Spectral Properties of Anomalous X-ray Pulsars

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chinese Journal of Astronomy and Astrophysics 2003年第6期3卷 543-550页

作者： Ye Lu, Wei Wang and Yong-Heng Zhaonational astronomical Observatories, chinese academy of sciences, beijing 100012 national astronomical Observatories CAS NAOC Beijing 100012 China

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.

关键词： pulsars: general stars: neutron X-rays: stars accretion: accretion disks

Polynomial regression calculation of the Earth's position based on millisecond pulsar timing

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Research in Astronomy and Astrophysics 2012年第2期12卷 219-234页

作者： Feng Tian 1,2,Zheng-Hong Tang 1,Qing-Zeng Yan 1,2 and Yong Yu 11 Shanghai astronomical observatory,chinese academy of sciences,Shanghai 200030,china 2 Graduate University of chinese academy of sciences,beijing 100049,china Shanghai astronomical observatory Chinese Academy of Sciences Shanghai 200030 China Graduate University of chinese academy of sciences Beijing 100049 China

Prior to achieving high precision navigation of a spacecraft using X-ray observations, a pulsar rotation model must be built and analysis of the precise posi- tion of the Earth should be performed using ground pulsar timing observations. We can simulate time-of-arrival ground observation data close to actual observed values before using pulsar timing observation data. Considering the correlation between the Earth＇s position and its short arc section of an orbit, we use polynomial regression to build the correlation. Regression coefficients can be calculated using the least square method, and a coordinate component series can also be obtained; that is, we can calcu- late Earth＇s position in the Barycentric Celestial Reference System according to pulse arrival time data and a precise pulsar rotation model. In order to set appropriate param- eters before the actual timing observations for Earth positioning, we can calculate the influence of the spatial distribution of pulsars on errors in the positioning result and the influence of error source variation on positioning by simulation. It is significant that the threshold values of the observation and systematic errors can be established before an actual observation occurs; namely, we can determine the observation mode with small errors and reject the observed data with big errors, thus improving the positioning result.

关键词： autonomous positioning - millisecond pulsar - pulsar timing - re-gression analysis

Evidence of a two-component jet in the afterglow of GRB 070419A

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Science china(Physics,Mechanics & Astronomy) 2010年第S1期53卷 265-266页

作者： ZHENG WeiKang1,2 & DENG JinSong1 1 national astronomical Observatories,chinese academy of sciences,beijing 100012,china 2 Graduate University of chinese academy of Science,beijing 100049,china 1. national astronomical Observatories Chinese Academy of Sciences Beijing 100012 China 2. Graduate University of chinese academy of Science Beijing 100049 China

A two-component jet model is proposed to explain the unusual afterglow of GRB *** the optical light curve,a wide "jet" with an opening angle of >30-40 degrees is assumed to produce the late shallow decay,while the three early power-law segments must be caused by a narrow jet with an opening angle of-2-4 *** energy injections to both components are *** X-ray emission may come from either the wide jet or the narrow *** the latter is correct,the jets may run into an ISM environment and the temporal index of the late energy injection may be q-0.65.

关键词： gamma-rays:bursts gamma-rays:observations

Formation of Solar Delta Active Regions:Twist and Writhe of Magnetic Ropes

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chinese Journal of Astronomy and Astrophysics 2004年第6期4卷 563-577页

作者： Hong-QiZhang nationalastronomicalObservatories ChineseAcademyofSciencesBeijing100012

We analyze the process of formation of delta configuration in some well-known super active regions based on photospheric vector magnetogram observations. It is found that the magnetic field in the initial developing stage of some delta active regions shows a potential-like configuration in the solar atmosphere, the magnetic shear develops mainly near the magnetic neutral line with magnetic islands of opposite polarities, and the large-scale photospheric twisted field forming gradually later. Some results are obtained: (1) The analysis of magnetic writhe of whole active regions cannot be limited in the strong field of sunspots, because the contribution of the fraction of decayed magnetic field is non-negligible. (2) The magnetic model of kink magnetic ropes, supposed to be generated in the subatmosphere, is not consistent with the evolution of large-scale twisted photospheric transverse magnetic field and not entirely consistent with the relationship with magnetic shear in some delta active regions. (3) The proposition is that the large-scale delta active regions are formed from contribution by small-scale non-potential magnetic flux bundles generated in the subatmosphere.

关键词： sun activity sun flares sun magnetic fields

Expectation for the X-ray Galactic Halo

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chinese Journal of Astronomy and Astrophysics 2002年第2期2卷 112-116页

作者： Zhi-Ying Huo national astronomical Observatories, chinese academy of sciences, beijing 100012 Department of Physics, Tianjin Normal University, Tianjin 300073 national astronomical Observatories Chinese Academy of Sciences Beijing 100012 []Department of Physics Tianjin Normal University Tianjin 300073

We present an estimate of the strength and spectrum of the X-ray background from the warm gas associated with the Galactic halo. This investigation is motivated primarily by the recent detection of a spatially variable soft X-ray component towards the north Galactic polar cap by Kuntz et al. (2001), suggesting that the warm gas heated by gravitational shocks of the Galactic halo may produce a significant contribution to the soft X-ray sky. Another purpose of the study is to refine the recent theoretical prediction of the X-ray spectrum from the Galactic halo by Xue (2001) who adopted an ideal and simple isothermal model for the gas and dark matter distributions of the Galactic halo. We use the universal density profile for the dark matter distributions of the Galactic halo to evaluate the X- ray properties of the warm gas either in hydrostatic equilibrium with, or tracing the underlying gravitational potential of the Galaxy. It has been shown that our prediction is consistent with the measured soft X-ray component towards the north Galactic polar cap if the gas fraction is taken to be^0.005.

关键词： cosmology: diffuse radiation -Galaxy: formation - X-rays: galaxies

Evolution of the Level of Sunspot Activity in Solar Cycles I. Evolution in the Descending Phase

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chinese Journal of Astronomy and Astrophysics 2006年第3期6卷 354-362页

作者： Jia-Long Wang national astronomical Observatories Chinese Academy of Sciences Beijing 100012

Taking the 13-point smoothed monthly sunspot number,Ri, and the deviation of the 13 associated monthly sunspot numbers from the smoothed one, Di, as a number-pair describing the global level of sunspot activity, the evolution of the level is statistically studied for the period from the month which is just 48 months before the minimum to the minimum in the descending phase, using the observed data of Solar Cycles 10 to 22. Our results show （1） for 46 months （94%） of the studied 49 months it is found that for a given month, the distribution of the 13 pairs which come from the 13 solar cycles on a log Ri - Di plane may be fitted by a straight line with a correlation coefficient larger than the critical one at confidence level a = 5%, and for 36 months （73%） the fitting is even better, for a = 1%; （2） time variations of these two parameters and their correlations in the studied period can be described respectively by functions of time, whose main trends may be expressed by a linear or simple curvilinear function; （3） the evolutionary path of the level of sunspot activity may be represented by a logarithmic function as log/~ = 0.704 lnDi - 0.291.

关键词： Sun - sunspots - active level evolution

Magnetic Helicity Injection in Solar Active Regions

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chinese Journal of Astronomy and Astrophysics 2006年第1期6卷 96-112页

作者： Hong-Qi Zhang national astronomical Observatories Chinese Academy of Sciences Beijing 100012

We present the evolution of magnetic field and its relationship with magnetic （current） helicity in solar active regions from a series of photospheric vector magnetograms obtained by Huairou Solar Observing Station, longitudinal magnetograms by MDI of SOHO and white light images of TRACE. The photospheric current helicity density is a quantity reflecting the local twisted magnetic field and is related to the remaining magnetic helicity in the photosphere, even if the mean current helicity density brings the general chiral property in a layer of solar active regions. As new magnetic flux emerges in active regions, changes of photospheric cur- rent helicity density with the injection of magnetic helicity into the corona from the subatmosphere can be detected, including changes in sign caused by the injection of magnetic helicity of opposite sign. Because the injection rate of magnetic helicity and photospheric current helicity density have different means in the solar atmosphere, the injected magnetic helicity is probably not proportional to the current helicity density remaining in the photosphere. The evidence is that rotation of sunspots does not synchronize exactly with the twist of photospheric transverse magnetic field in some active regions （such as, delta active regions）. They represent different aspects of magnetic chirality. A combined analysis of the observational magnetic helicity parameters actually provides a relative complete picture of magnetic helicity and its transfer in the solar atmosphere.

关键词： Sun: activity Sun: magnetic fields