Low-state disks and low-beta disks
Low-state disks and low-beta disks
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低状态磁盘和低 beta 磁盘
DOI：
10.1086/187885
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发表时间：
1995
期刊：
影响因子：
--
通讯作者：
R. Matsumoto
中科院分区：
文献类型：
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作者：
S. Mineshige;Masaaki Kusnose;R. Matsumoto
恒星黑洞候选者（BHC）表现出双峰光谱状态。我们计算了非热磁盘光谱，表明在软（高）状态下观察到的大光子指数（α（sub x）约2 - 3）是由于丰富的软光子供应，而软光子饥饿导致在硬（低）状态下的较小指数（α（sub x）约1.5 - 2）。因此，在低状态下不存在软分量通量不可能是由于遮蔽。一个可能的磁盘配置期间的低状态进行了讨论。我们提出，由于强剪切抑制了场逃逸，低态盘可能是磁压超过气压的低β盘。结果，磁盘材料将采取主要由环形磁场约束的斑点的形式。场的消散主要是由于偶尔发生的重联事件和巨大的能量释放。这将解释大振幅，非周期性的X射线变化（闪烁）和高能量辐射与小阿尔法（子x）从硬状态BHC和可能从活动星系核。此外，我们提出了一个滞后的质量流量和等离子体β，气体压力的磁压力比之间的关系，瞬态BHC的光谱演化。盘在静止和早期上升时处于低β状态。低β盘在光学上是薄的，并受到平流的影响。由于在较高的光度下没有平流主导的分支，所以在峰值光度之前发生硬到软的转变。在小半径处出现一个光学上厚的高β盘。在光变曲线的衰减阶段，当触发软硬转变时，标准型盘变得有效地光学薄。主体中的高β等离子体收缩形成微小的斑点，低β日冕等离子体填充斑点间的空间。
Stellar black hole candidates (BHCs) exhibit bimodal spectral states. We calculate nonthermal disk spectra, demonstrating that a large photon index (alpha (sub x) approximately 2-3) observed in the soft (high) state is due to a copious soft photon supply, whereas soft photon starvation leads to a smaller index (alpha (sub x) approximately 1.5-2) in the hard (low) state. Thus, the absence of the soft component flux in the low state cannot be due to obscuration. A possible disk configuration during the low state is discussed. We proposed that a low-state disk may be a low-beta disk in which magnetic pressure may exceed gas pressure becuase of the suppression of field escape by a strong shear. As a result, disk material will take the form of blobs constricted by mainly toroidal magnetic fields. Fields are dissipated mainly by occasional reconnection events with a huge energy release. This will account for large-amplitude, aperiodic X-ray variations (flickering) and high-energy radiation with small alpha(sub x) from hard state BHCs and possibly from active galactic nuclei. Further, we propose a hysteretic relation between the mass-flow rate and plasma-beta, a ratio of gas pressure to magnetic pressure, for the spectral evolution of transient BHCs. The disk is in the low-beta state in quiescence and early rise. The low-beta disk is optically thin and affected by advection. A hard-to-soft transition occurs before the peak luminosity, since there is no advection-dominated branch at higher luminosities. An optically thick, high-beta disk appears at small radii. In the decay phase of the light curve, the standard-type disk becomes effectively optically thin, when a soft-hard transition is triggered. High-beta plasmas in the main body shrink to form minute blobs, and low-beta coronal plasma fills interblob space.