AGN中的热粘盘不稳定性模型
The thermal-viscous disk instability model in the AGN context
摘要：
活动星系核中的吸积盘与激变变星（CV）或低质量X射线双星（LMXB）中的吸积盘一样，也会受到同样类型的不稳定性的影响，从而导致矮新星和软X射线瞬态爆发。有人认为，这种热/粘性不稳定性可以解释活动星系核的长期变化。我们测试这一论断提出了一个系统的研究应用磁盘不稳定性模型（DIM）活动星系核。我们正在使用自适应网格的数值代码，我们已经开发的CV的背景下，使我们能够完全解决的径向结构的磁盘。我们表明，因为在活动星系核盘的马赫数是非常大的，加热和冷却的前锋是如此之窄，他们不能解决的数值代码，一直使用到现在。此外，这些前沿传播的时间尺度比粘性时间短得多。因此，一系列的加热和冷却的前锋来回传播的磁盘，导致只有小的变化的吸积率到黑洞，与短期的静态发生非常低的质量传递速率。通过例如ADAF截断盘的内部部分不会改变该结果，但能够实现更长的静止状态。最后，我们讨论了辐射的影响，由中央X射线源，并表明，即使是非常高的辐射效率，爆发是不是一个自然的结果模型。
英文摘要：
Accretion disks in AGN should be subject to the same type of instability as in cataclysmic variables (CVs) or in low-mass X-ray binaries (LMXBs), which leads to dwarf nova and soft X-ray transient outbursts. It has been suggested that this thermal/viscous instability can account for the long term variability of AGNs. We test this assertion by presenting a systematic study of the application of the disk instability model (DIM) to AGNs. We are using the adaptative grid numerical code we have developed in the context of CVs, enabling us to fully resolve the radial structure of the disk. We show that, because in AGN disks the Mach numbers are very large, the heating and cooling fronts are so narrow that they cannot be resolved by the numerical codes that have been used until now. In addition, these fronts propagate on time scales much shorter than the viscous time. As a result, a sequence of heating and cooling fronts propagate back and forth in the disk, leading only to small variations of the accretion rate onto the black hole, with short quiescent states occurring for very low mass transfer rates only. Truncation of the inner part of the disk by e.g. an ADAF does not alter this result, but enables longer quiescent states. Finally we discuss the effects of irradiation by the central X-ray source, and show that, even for extremely high irradiation efficiencies, outbursts are not a natural outcome of the model.
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