An application of the Kerr black hole fly-wheel model to statistical properties of QSOs/AGNs     

Shin-ya Nitta 《Monthly notices of the Royal Astronomical Society》1999,308(4):995-1005

The aim of this work is to demonstrate the properties of the magnetospheric model around Kerr black holes (BHs), the so-called fly-wheel (rotation driven) model. The fly-wheel engine of the BH–accretion disc system is applied to the statistics of QSOs/AGNs. In the model, the central BH is assumed to be formed at z ∼10² and obtains nearly maximum but finite rotation energy (∼extreme Kerr BH) at the formation stage. The inherently obtained rotation energy of the Kerr BH is released through a magnetohydrodynamic process. This model naturally leads to a finite lifetime of AGN activity.
Nitta, Takahashi & Tomimatsu clarified the individual evolution of the Kerr BH fly-wheel engine, which is parametrized by BH mass, initial Kerr parameter, magnetic field near the horizon and a dimensionless small parameter. We impose a statistical model for the initial mass function (IMF) of an ensemble of BHs using the Press–Schechter formalism. With the help of additional assumptions, we can discuss the evolution of the luminosity function and the spatial number density of QSOs/AGNs.
By comparing with observations , it is found that a somewhat flat IMF and weak dependence of the magnetic field on the BH mass are preferred. The result explains well the decrease of very bright QSOs and decrease of population after z ∼2.  相似文献   

The spatial distribution of coalescing neutron star binaries: implications for gamma-ray bursts     

Joshua S. Bloom  Steinn Sigurdsson  Onno R. Pols 《Monthly notices of the Royal Astronomical Society》1999,305(4):763-769

  相似文献   

Gamma-ray bursts: post-burst evolution of fireballs   总被引：3，自引：0，他引：3  

Y. F. Huang  Z. G. Dai  D. M. Wei  & T. Lu 《Monthly notices of the Royal Astronomical Society》1998,298(2):459-463

The post-burst evolution of fireballs that produce γ-ray bursts (GRBs) is studied, assuming the expansion of fireballs to be adiabatic and relativistic. Numerical results as well as an approximate analytic solution for the evolution are presented. Owing to the adoption of a new relation between t R and γ, our results differ markedly from previous studies. Synchrotron radiation from the shocked interstellar medium is carefully calculated, using a conventional set of equations. The observed X-ray flux of GRB afterglows can be reproduced easily. Although the optical afterglows seem much more complicated, our results can still present a rather satisfactory agreement with observations. We also find that the expansion will no longer be highly relativistic about 4 d after the main GRB. We thus suggest that the marginally relativistic phase of the expansion should be investigated so as to check the afterglows observed a week or more later.  相似文献   

Slim accretion discs: a model for ADAF–SLE transitions     

Igor V. Igumenshchev  Marek A. Abramowicz  & Igor D. Novikov 《Monthly notices of the Royal Astronomical Society》1998,298(4):1069-1078

We numerically construct slim, global, vertically integrated models of optically thin, transonic accretion discs around black holes, assuming a regularity condition at the sonic radius and boundary conditions at the outer radius of the disc and near the black hole. In agreement with several previous studies, we find two branches of shock-free solutions, in which the cooling is dominated either by advection or by local radiation. We also confirm that the part of the accretion flow where advection dominates is in some circumstances limited in size: it does not extend beyond a certain outer limiting radius. New results found in our paper concern the location of the limiting radius and the properties of the flow near to it. In particular, we find that beyond the limiting radius the advective-dominated solutions match on to Shapiro, Lightman &38; Eardley (SLE) discs through a smooth transition region. Therefore, the full global solutions are shock-free and unlimited in size. There is no need to postulate an extra physical effect (e.g. evaporation) for triggering the ADAF–SLE transition. It occurs as a result of standard accretion processes described by the classic slim disc equations.  相似文献   

Non-axisymmetric relativistic Bondi–Hoyle accretion on to a Schwarzschild black hole     

José A. Font  & J. M. Ibáñez 《Monthly notices of the Royal Astronomical Society》1998,298(3):835-846

We present the results of an exhaustive numerical study of fully relativistic non-axisymmetric Bondi–Hoyle accretion on to a moving Schwarzschild black hole. We have solved the equations of general relativistic hydrodynamics with a high-resolution shock-capturing numerical scheme based on a linearized Riemann solver. The numerical code was previously used to study axisymmetric flow configurations past a Schwarzschild black hole. We have analysed and discussed the flow morphology for a sample of asymptotically high Mach number models. The results of this work reveal that initially asymptotic uniform flows always accrete on to the hole in a stationary way, which closely resembles the previous axisymmetric patterns. This is in contrast with some Newtonian numerical studies where violent flip-flop instabilities were found. As discussed in the text, the reason can be found in the initial conditions used in the relativistic regime, as they cannot exactly duplicate the previous Newtonian setups where the instability appeared. The dependence of the final solution on the inner boundary condition as well as on the grid resolution has also been studied. Finally, we have computed the accretion rates of mass and linear and angular momentum.  相似文献   

DSC2型称重式降水传感器测雨性能的分析   总被引：1，自引：0，他引：1  

李林  范雪波  孙雪琪  崔炜  张治国 《气象》2016,42(8):1013-1019

为更有效地利用降雨观测数据,充分发挥新型探测设备建设效益,文章对DS(2型称重降水传感器的测雨性能进行分析评估,选取北京市13个国家级地面气象观测站在2013年4—10月,称重式降水传感器与人工、翻斗观测降雨量的业务观测资料,分析称重与人工和翻斗观测在降雨总量、日降雨量等方面的差异。结果表明:在选取样本中,12个台站的总降雨量误差符合现行业务要求,三种测量在日降雨量等级判断方面基本一致。称重比人工观测的日降雨量平均偏小0.13 mm,日降雨量相关系数为0.9968,对应地,称重比翻斗观测的结果平均偏小0.17 mm,日降雨量相关系数为0.9983。  相似文献   

The Momentum 4-Vector Imparted by Gravitational Waves in Bianchi-Type Metrics     

Ali Havare  Murat Korunur  Mustafa Salti 《Astrophysics and Space Science》2006,301(1-4):43-46

Considering the Møller, Weinberg and Qadir-Sharif's definitions in general relativity, we find the momentum 4-vector of the closed universe based on the Bianchi-type metrics. The momentum 4-vector (due to matter plus fields) is found to be zero. This result supports the viewpoints of Albrow and Tryon and extends the previous works by Cooperstock–Israelit, Rosen, Johri et al., Banerjee–Sen and Vargas who investigated the problem of the energy in Friedmann–Robertson–Walker universe and Salt?-Havare who studied the problem of the energy-momentum of the viscous Kasner-type space-times.  相似文献   

Opening angles, Lorentz factors and confinement of X-ray binary jets     

J. C. A. Miller-Jones  R. P. Fender  E. Nakar 《Monthly notices of the Royal Astronomical Society》2006,367(4):1432-1440

We present a collation of the available data on the opening angles of jets in X-ray binaries, which in most cases are small (≲10°). Under the assumption of no confinement, we calculate the Lorentz factors required to produce such small opening angles via the transverse relativistic Doppler effect. The derived Lorentz factors, which are in most cases lower limits, are found to be large, with a mean >10, comparable to those estimated for active galactic nuclei (AGN) and much higher than the commonly assumed values for X-ray binaries of 2–5. Jet power constraints do not, in most cases, rule out such high Lorentz factors. The upper limits on the opening angles show no evidence for smaller Lorentz factors in the steady jets of Cygnus X-1 and GRS 1915+105. In those sources in which deceleration has been observed (notably  XTE J1550−564  and Cygnus X-3), some confinement of the jets must be occurring, and we briefly discuss possible confinement mechanisms. It is however possible that all the jets could be confined, in which case the requirement for high bulk Lorentz factors can be relaxed.  相似文献   

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   

Relativistic gravitational collapse of a cool white dwarf with allowance for the neutronization kinetics     

A. I. Voropinov  M. A. Podurets 《Astronomy Letters》2001,27(6):366-375

We consider and numerically solve the problem of the relativistic gravitational collapse of a spherically symmetric cool nonrotating white dwarf with allowance for the neutronization kinetics. We propose a model equation of state and analyze the neutronization kinetics under simplifying assumptions. A comprehensive mathematical model is constructed for the phenomenon. The system of equations is integrated numerically. The gravitational collapse of a white dwarf that lost its stability is shown to lead to the envelope ejection and to the final state of a hot static neutron star. For comparison, we solve the problem with an equilibrium equation of state. We show that in this case, the entire mass ultimately goes under the gravitational radius to form a black hole.  相似文献