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arXiv 0907.2068astro-ph.HE
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湍流吸积盘中大尺度磁场引起的日冕

Coronae as Consequence of Large Scale Magnetic Fields in Turbulent Accretion Disks

Eric G. Blackman, Martin E. Pessah

摘要:

致密吸积引擎中的非热X射线发射可以解释为在光学厚的吸积盘上方的光学薄磁化日冕中的磁耗散。如果日冕磁场起源于圆盘,而圆盘是湍流的,那么只有足够大的磁性结构才能在到达日冕的过程中幸存下来,它们的湍流破碎时间超过了它们的浮力上升时间。我们使用这个概念和一个物理模型来约束的最小比例的磁能以上的浮力作为观测到的日冕辐射热发射的函数的临界尺度。我们的研究结果表明,在吸积盘中的磁能的显着部分驻留在大规模的领域,这反过来又提供了间接的证据,显着的非本地传输现象和需要大规模的磁场产生。以塞弗特活动星系核为例,其辐射热通量的30%量级在X射线波段,我们发现,超过20%的磁能必须有足够大的尺度才能在日冕中上升和消散。

英文摘要:

Non-thermal X-ray emission in compact accretion engines can be interpreted to result from magnetic dissipation in an optically thin magnetized corona above an optically thick accretion disk. If coronal magnetic field originates in the disk and the disk is turbulent, then only magnetic structures large enough for their turbulent shredding time to exceed their buoyant rise time survive the journey to the corona. We use this concept and a physical model to constrain the minimum fraction of magnetic energy above the critical scale for buoyancy as a function of the observed coronal to bolometric emission. Our results suggest that a significant fraction of the magnetic energy in accretion disks resides in large scale fields, which in turn provides circumstantial evidence for significant non-local transport phenomena and the need for large scale magnetic field generation. For the example of Seyfert AGN, for which of order 30 per cent of the bolometric flux is in the X-ray band, we find that more than 20 per cent of the magnetic energy must be of large enough scale to rise and dissipate in the corona.

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