An HLLC Riemann solver for relativistic flows – II. Magnetohydrodynamics     

A. Mignone  G. Bodo 《Monthly notices of the Royal Astronomical Society》2006,368(3):1040-1054

An approximate Riemann solver for the equations of relativistic magnetohydrodynamics (RMHD) is derived. The Harten–Lax–van Leer contact wave (HLLC) solver, originally developed by Toro, Spruce and Spears, generalizes the algorithm described in a previous paper to the case where magnetic fields are present. The solution to the Riemann problem is approximated by two constant states bounded by two fast shocks and separated by a tangential wave. The scheme is Jacobian-free, in the sense that it avoids the expensive characteristic decomposition of the RMHD equations and it improves over the HLL scheme by restoring the missing contact wave.
Multidimensional integration proceeds via the single step, corner transport upwind (CTU) method of Colella, combined with the constrained transport (CT) algorithm to preserve divergence-free magnetic fields. The resulting numerical scheme is simple to implement, efficient and suitable for a general equation of state. The robustness of the new algorithm is validated against one- and two-dimensional numerical test problems.  相似文献   

Studies of accretion flows around rotating black holes – II. Standing shocks in the pseudo-Kerr geometry     

Soumen Mondal  Sandip K. Chakrabarti 《Monthly notices of the Royal Astronomical Society》2006,371(3):1418-1426

Standing, propagating or oscillating shock waves are common in accretion and winds around compact objects. We study the topology of all possible solutions using the pseudo-Kerr geometry. We present the parameter space spanned by the specific energy and angular momentum and compare it with that obtained from the full general relativity to show that the potential can work satisfactorily in fluid dynamics also, provided the polytropic index is suitably modified. We then divide the parameter space depending on the nature of the solution topology. We specifically study the nature of the standing Rankine–Hugoniot shocks. We also show that as the Kerr parameter is increased, the shock location generally moves closer to the black hole. In future, these solutions can be used as guidelines to test numerical simulations around compact objects.  相似文献   

Self-similar shocks in polytropic gas flows around star-forming regions     

Yu-Qing Lou  Yang Gao 《Monthly notices of the Royal Astronomical Society》2006,373(4):1610-1618

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Observations of high co rotational lines in post-AGBs and PN     

K. Justtanont  A. G. G. M. Tielens  C. J. Skinner  M. R. Haas 《Astrophysics and Space Science》1995,224(1-2):305-308

We present a preliminary interpretation of high CO rotational line data obtained from KAO. The possibility of either a PDR or a shock model is considered in order to explain the observations.  相似文献   

1993年7月湖北咸宁4.1级地震序列的活动特征     

杨福平  周昕  严尊国 《大地测量与地球动力学》2001,21(4):81-86

1993年 7月底至 8月中旬在咸宁发生的ML4 .1震群是一比较典型的有感震群 ,通过多种测震手段对该震群进行分析和处理 ,得到下列认识和结果 :1、该震群是一个非前兆震群。 2、此震群是一个主震型震群 ,地震主要发生在两个阶段 ,每个阶段均出现密集 -平静过程。 3、该震群可能与NE向潜山断裂的活动有关。 4、对咸宁震群的各种测震学参数计算表明 ,有一些参数在湖北省比较适用 (如b ,η ,U ,K ,ρ等 ) ,而有些则不适合 (如h ,F 等 )。  相似文献   

Gamma—Ray Bursts：Afterglows and Central Engines   总被引：5，自引：0，他引：5  

K.S.Cheng T.Lu 《中国天文和天体物理学报》2001,1(1):1-20

Gamma-ray bursts (GRBs) are the most intense transient gamma-ray events in the sky; this, together with the strong evidence (the isotropic and inhomogeneous distribution of GRBs detected by BASTE) that they are located at cosmological distances, makes them the most energetic events ever known. For example, the observed radiation energies of some GRBs are equivalent to the total convertion into radiation of the mass energy of more than one solar mass. This is thousand times stronger than the energy of a supernova explosion. Some unconventional energy mechanism and extremely high conversion efficiency for these mysterious events are required. The discovery of host galaxies and association with supernovae at cosmoligical distances by the recently launched satellite of BeppoSAX and ground based radio and optical telescopes in GRB afterglow provides further support to the cosmological origin of GRBs and put strong constraints on their central engine. It is the aim of this article to review the possible central engines, energy mechanisms, dynamical and spectral evolution of GRBs, especially focusing on the afterglows in multi-wavebands.  相似文献   

空间无碰撞激波的数值研究   总被引：2，自引：0，他引：2  

王水  陆全明 《天文学进展》1997,15(3):218-230

无碰撞激波是空间等离子体和宇宙等离子体中的重要物理现象。文中评述了数值研究空间无碰撞激波的两种方法－粒子模拟和混合模拟，给出了准垂直和准平行无碰撞激波的数值研究结果。还指出了一些尚未解决的研究问题。  相似文献   

Blazar天体中光学射电大爆发的频谱演化     

钱善Jie 《天文学报》1997,38(3):239-249

本文讨论Ｂｌａｚａｒ天体中光学射电大爆发频谱演化的理论模型．考虑沿喷流传播的相对论性激波所注入或加速的相对论性电子，受到康普顿、同步辐射和绝热膨胀三种损耗，并计及相对论电子能谱的高能截断．假定喷流轴线与观测者方向构成很小角度．文中给出了大爆发频谱三阶段连续演化的特性，即康普顿阶段，同步辐射阶段和绝热膨胀阶段的爆发特性．频谱演化用（Ｓｍ－ｖｍ）关系表达（见图２，图中Ｓｍ为频谱反转流量，ｖｍ为反转频率），它与一些Ｂｌａｚａｒ天体中观测到的典型形式相符合．  相似文献   

Shock temperatures in anorthite glass     

Mark B. Boslough  Thomas J. Ahrens  Arthur C. Mitchell 《Geophysical Journal International》1986,84(3):475-489

Summary. Temperatures of CaAl₂Si₂O₈ (anorthite glass) shocked to pressures between 48 and 117 GPa have been measured in the range from 2500 to 5600 K, using optical pyrometry techniques. The pressure dependence of the shock temperatures deviates significantly from predictions based on a single high-pressure phase. Either a variable specific heat, or the existence of three phase transitions, at pressures of about 55, 85 and 100 GPa and with transition energies of about 0.5 MJ kg⁻¹ each (∼ 1.5 MJ kg⁻¹ total) can explain the shock-temperature data. The proposed phase transition at 100 GPa can possibly be identified with the stishovite melting transition. Theoretical models of the time dependence of the thermal radiation from the shocked anorthite based on the geometry of the experiment and the absorptive properties of the shocked material yield good agreement with observations, indicating that it is not necessary to invoke intrinsic time dependences to explain the data in many cases. Observed time dependences were used to calculate absorption coefficients of the shocked material of from about 2 mm⁻¹ to greater than 24 mm⁻¹– an increasing function of shock pressure. The assumption that the shocked material radiates as a black body is supported by the theoretical model, and by the close agreement between measured and calculated black body spectral radiance as a function of wavelength.  相似文献   

Low velocity shock-cloud encounters I.     

András Horváth Jr.  L. Viktor Tóth 《Astrophysics and Space Science》1995,233(1-2):169-173

Shocks propagating in the interstellar medium (ISM) play an important role in the life of molecular clouds. Through a theoretical study of interaction between clouds and shocks we can understand, for example, the density distribution of observed molecular clouds and the first steps of star formation. The only way to study of interaction in detail is via a numerical hydrodynamical simulation. In this paper we present the first results of a hydrocode which is able to follow the processes after the collision between the cloud and shock front.Our main theoretical result is that the chemical processes (e.g. H₂ dissociation) can affect the dynamical processes significantly. Global parameters of the cloud are calculated for the comparision of the simulation and the observations.  相似文献