Space‐time curvature and recession velocities

The problem of interpretation of recession velocities reflects straightforwardly the curvature of space‐time. In a recent article it was claimed that this problem would show that the General Relativity Theory had to and would overrule the Special Relativity Theory (Davis & Lineweaver 2003; Lineweaver & Davis 2005). This must be corrected. It is shown that the simplistic definition of the recession velocity as change in distance on a space of constant cosmological time yields in fact a pseudo‐euclidean angle and that the simplest correct definition of the recession velocity fits perfectly with the SRT formula for the Doppler effect. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Models for the X‐ray spectra and variability of luminous accreting black holes

The X‐ray spectra of luminous Seyfert 1 galaxies often appear to be reflection dominated. In a number of Narrow Line Seyfert 1 (NLS1) galaxies and galactic black holes in the very high state, the variability of the continuum and of the iron line are decoupled, the reflected component being often much less variable than the continuum. These properties have been interpreted as effects of gravitational light bending. In this framework, we present detailed Monte‐Carlo simulations of the reflection continuum in the Kerr metric. These calculations confirm that the spectra and variability behaviour of these sources can be reproduced by the light bending model. As an alternative to the light bending model, we show that similar observational properties are expected from radiation pressure dominated discs subject to violent clumping instabilities and, as a result, have a highly inhomogeneous two‐phase structure. In this model, most of the observed spectral and variability features originate from the complex geometrical structure of the inner regions of near‐Eddington accretion flows and are therefore a signature of accretion physics rather than general relativity. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magnetic flares in Active Galactic Nuclei: modeling the iron Kα line

The X‐ray spectra of Active Galactic Nuclei (AGN) are complex and vary rapidly in time as seen in recent observations. Magnetic flares above the accretion disk can account for the extreme variability of AGN. They also explain the observed iron Kα fluorescence lines. We present radiative transfer modeling of the X‐ray reflection due to emission from magnetic flares close to the marginally stable orbit. The hard X‐ray primary radiation coming from the flare source illuminates the accretion disk. A Compton reflection/reprocessed component coming from the disk surface is computed for different emission directions. We assume that the density structure remains adjusted to the hydrostatic equilibrium without external illumination because the flare duration is only a quarter‐orbit. The model takes into account the variations of the incident radiation across the hot spot underneath the flare source. The integrated spectrum seen by a distant observer is computed for flares at different orbital phases close to the marginally stable orbit of a Schwarzschild black hole and of a maximally rotating Kerr black hole. The calculations include relativistic and Doppler corrections of the spectra using a ray tracing technique. We explore the practical possibilities to map out the azimuthal irradiation pattern of the inner accretion disks and conclude that the next generation of X‐ray satellites should reveal this structure from iron Kα line profiles and X‐ray lightcurves. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

工程化广播星历参数拟合算法与接口设计

对导航卫星广播星历参数拟合算法和接口设计问题进行了研究。通过条件数、参数相关性分析,指出小倾角问题是造成GPS开普勒轨道根数广播星历拟合算法不能适用于GEO卫星的最主要原因;通过分析定轨理论和拟合实例证明,GEO卫星星历参数Crc、Crs超限的主要原因是由于其轨道特性决定的;针对GEO卫星星历参数拟合法方程严重病态的问题,提出了动态加权的带参数约束条件平差算法。该方法能有效稳定星历拟合结果,解决Δn等星历参数超限的问题。     

New upper limit on the cosmological constant from solar system dynamics

The cosmological constantΛis the simplest model for explaining the dark energy which supposedly drives the observed accelerated expansion rate of the Universe.Together with the concept of cold dark matter,it satisfactorily accommodates a wealth of observations related to cosmology.Due to its assumed constancy throughout the Universe,Λmight also affect the dynamics of the planets in the solar system,although with extremely small effects.However,modern high-precision ephemerides provide a promising tool for constraining it.Using the supplementary advances in the perihelia provided by current INPOP10a and EPM2011 ephemerides,we obtain a new upper limit onΛin the solar system when the Lense-Thirring effect due to the Sun’s angular momentum and the uncertainty of the Sun’s quadrupole moment are properly taken into account.These two factors were mostly absent in previous works dealing withΛ.We find that INPOP10a yields an upper limit ofΛ=(0.26±1.45)×10-43m-2and EPM2011 givesΛ=(-0.44±8.93)×10-43m-2.Such bounds are about 10 times less than previously estimated results.     

Quasi-radial modes of rotating stars in general relativity

By using the Cowling approximation, quasi-radial modes of rotating general relativistic stars are computed along equilibrium sequences from non-rotating to maximally rotating models. The eigenfrequencies of these modes are decreasing functions of the rotational frequency. The eigenfrequency curve of each mode as a function of the rotational frequency has discontinuities, which arise from the avoided crossing with other curves of axisymmetric modes.