蒸发馈电电晕的结构与磁场蒸发特性
Disk-Evaporation Fed Corona: Structure and Evaporation Feature with Magnetic Field
摘要：
盘冠蒸发模型自然地解释了黑洞X射线双星中的许多观测现象，如吸积盘的截断和光谱态跃迁。另一方面，已知磁场在吸积流中输送角动量和产生粘性方面起重要作用。在这项工作中，我们明确考虑了吸积盘日冕中的磁场，并在我们的双温蒸发程序的基础上数值计算了日冕结构。我们发现，磁场通过对日冕中的压力、能量和辐射冷却的贡献以及通过减少垂直热传导来影响日冕结构。我们发现，当磁场强度变化时，最大蒸发速率（$\sim 0.03$爱丁顿速率）基本保持不变，但最大蒸发速率对应的半径随磁场的增大而减小。这预示着谱态跃迁总是发生在几个百分点的爱丁顿吸积率，而薄盘的内边缘可以在$\sim 100 R_{\rm S} $或更少的硬态之前过渡到软态。这些结果缓解了以前的蒸发模型预测的截断半径太大的问题，并与几个黑洞X射线双星的观测结果更好地吻合，但仍存在差异。
英文摘要：
The disk-corona evaporation model naturally interprets many observational phenomena in black hole X-ray binaries, such as the truncation of an accretion disk and the spectral state transitions. On the other hand, magnetic field is known to play an important role in transporting angular momentum and producing viscosity in accretion flows. In this work, we explicitly take the magnetic field in the accretion disk corona into account and numerically calculate the coronal structure on the basis of our two-temperature evaporation code. We show that the magnetic field influences the coronal structure by its contribution to the pressure, energy and radiative cooling in the corona and by decreasing the vertical heat conduction. We found that the maximal evaporation rate keeps more or less constant ($\sim 0.03$ Eddington rate) while the strength of magnetic fields changes, but that the radius corresponding to the maximal evaporation rate decreases with increasing magnetic field. This predicts that the spectral state transition always occurs at a few percent of Eddington accretion rate, while the inner edge of thin disk can be at $\sim 100 R_{\rm S} $ or even less in the hard state before the transition to the soft state. These results alleviate the problem that previous evaporation models predict too large a truncation radius, and are in better agreement with the observational results of several black hole X-ray binaries, though discrepancies remain.
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