THERMAL EQUILIBRIA OF MAGNETICALLY SUPPORTED BLACK HOLE ACCRETION DISKS
THERMAL EQUILIBRIA OF MAGNETICALLY SUPPORTED BLACK HOLE ACCRETION DISKS
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DOI：
10.1088/0004-637x/697/1/16
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发表时间：
2009-03
期刊：
影响因子：
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通讯作者：
H. Oda;M. Machida;K. Nakamura;R. Matsumoto
中科院分区：
文献类型：
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作者：
H. Oda;M. Machida;K. Nakamura;R. Matsumoto
我们提出了包含磁场的光薄和光厚圆盘的新的热平衡解。本文的目的是解释在候选黑洞爆发上升阶段观测到的明亮硬态和亮/慢跃迁。基于三维磁流体力学模拟的结果，我们假设圆盘内的磁场是湍流的，由方位分量主导，并且方位平均麦克斯韦应力与总（气体、辐射和磁）压力成正比。我们规定了磁通量平流率来确定给定半径处的方位磁通量。局部热平衡解是通过将加热、辐射冷却和热平流项相等得到的。我们发现了磁支持（β = (pgas + prad)/pmag < 1）的光薄和光厚磁盘的热稳定解决方案，其中强磁场增强的加热平衡了辐射冷却。低β盘的温度（T ~ 107 ~ 1011k）低于以平流为主的吸积流（或辐射低效吸积流），但高于标准盘。我们还研究了热平衡解的径向依赖性。光学薄的低β分支延伸至，其中为质量吸积率，为Eddington质量吸积率，其中温度与质量吸积率反相关。因此，光学薄的低β盘可以解释明亮的硬态。光学厚的低β盘的有效温度Teff∝ω−3/4与径向相关。这样的磁盘将被观察到保持在高/软状态。此外，由于光学厚的低β盘分支与辐射压力主导的标准盘分支相交，在光学厚的低β盘和薄盘之间会发生极限环振荡。这些极限环振荡将显示出比标准圆盘和薄圆盘之间更小的光度变化。
We present new thermal equilibrium solutions for optically thin and optically thick disks incorporating magnetic fields. The purpose of this paper is to explain the bright hard state and the bright/slow transition observed in the rising phases of outbursts in black hole candidates. On the basis of the results of three-dimensional magnetohydrodynamic simulations, we assume that magnetic fields inside the disk are turbulent and dominated by the azimuthal component and that the azimuthally averaged Maxwell stress is proportional to the total (gas, radiation, and magnetic) pressure. We prescribe the magnetic flux advection rate to determine the azimuthal magnetic flux at a given radius. Local thermal equilibrium solutions are obtained by equating the heating, radiative cooling, and heat advection terms. We find magnetically supported (β = (pgas + prad)/pmag < 1), thermally stable solutions for both optically thin disks and optically thick disks, in which the heating enhanced by the strong magnetic field balances the radiative cooling. The temperature in a low-β disk (T ∼ 107–1011K) is lower than that in an advection-dominated accretion flow (or radiatively inefficient accretion flow) but higher than that in a standard disk. We also study the radial dependence of the thermal equilibrium solutions. The optically thin, low-β branch extends to , where is the mass accretion rate and is the Eddington mass accretion rate, in which the temperature anticorrelates with the mass accretion rate. Thus, optically thin low-β disks can explain the bright hard state. Optically thick, low-β disks have the radial dependence of the effective temperature Teff ∝ ϖ−3/4. Such disks will be observed as staying in a high/soft state. Furthermore, limit cycle oscillations between an optically thick low-β disk and a slim disk will occur because the optically thick low-β branch intersects with the radiation pressure dominated standard disk branch. These limit cycle oscillations will show a smaller luminosity variation than that between a standard disk and a slim disk.