Dead Zone Formation and Nonsteady Hyperaccretion in Collapsar Disks: A Possible Origin of Short-Term Variability in the Prompt Emission of Gamma-Ray Bursts
Dead Zone Formation and Nonsteady Hyperaccretion in Collapsar Disks: A Possible Origin of Short-Term Variability in the Prompt Emission of Gamma-Ray Bursts
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DOI：
10.1086/518088
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发表时间：
2006-12
期刊：
影响因子：
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通讯作者：
Y. Masada;N. Kawanaka;T. Sano;K. Shibata
中科院分区：
文献类型：
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作者：
Y. Masada;N. Kawanaka;T. Sano;K. Shibata
伽马射线暴的中心引擎被认为是一个热而致密的盘，它与一些太阳质量的黑洞发生了超吸积。我们调查的磁旋转不稳定性（MRI）积极运作的超吸积盘，这可能会导致角动量输运的磁盘。超吸积盘的内部区域可以是中微子不透明的，中微子的能量和动量输运可以显著影响磁共振成像的生长。在合理的吸积盘模型和弱磁场B = 10 14 G的假设下，发现在超吸积盘的内部区域，磁共振成像受到中微子粘性的强烈抑制。另一方面，磁共振成像可以驱动主动磁流体动力学湍流的中微子透明的外部区域，而不管场强。这表明重子物质被积累到内部死区，在那里MRI不活跃地生长，角动量传输效率低下。当死区获得大量的质量并变得引力不稳定时，通过引力矩，中心黑洞会发生强烈的质量吸积。这一过程可能是伽玛暴瞬时发射短期变化的物理机制。最后，在我们的情节吸积情景的背景下，在X射线余辉的耀斑活动的起源进行了预测。
The central engine of gamma-ray bursts (GRBs) is believed to be a hot and dense disk with hyperaccretion onto a few solar-mass black hole. We investigate where the magnetorotational instability (MRI) actively operates in the hyperaccretion disk, which can cause angular momentum transport in the disk. The inner region of hyperaccretion disks can be neutrino opaque, and the energy and momentum transport by neutrinos could affect the growth of the MRI significantly. Assuming reasonable disk models and a weak magnetic field B ≲ 1014 G, it is found that the MRI is strongly suppressed by the neutrino viscosity in the inner region of hyperaccretion disks. On the other hand, the MRI can drive active magnetohydrodynamic turbulence in the outer neutrino-transparent region regardless of the field strength. This suggests that the baryonic matter is accumulated into the inner dead zone, where the MRI grows inactively and the angular momentum transport is inefficient. When the dead zone gains a large amount of mass and becomes gravitationally unstable, intense mass accretion onto the central black hole would occur episodically through the gravitational torque. This process can be a physical mechanism of the short-term variability in the prompt emission of GRBs. Finally, the origin of flaring activities in the X-ray afterglow is predicted in the context of our episodic accretion scenario.