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arXiv 1010.0903astro-ph.HE
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伽马射线暴中央引擎不稳定。是什么让喷射流变了?

Instabilities in the Gamma Ray Burst central engine. What makes the jet variable?

Agnieszka Janiuk, Ye-Fei Yuan, Rosalba Perna, Tiziana Di Matteo

摘要:

这两种类型的长和短伽马射线暴都涉及到一个阶段的超爱丁顿吸积的热和密集的等离子体环到一个新诞生的黑洞。瞬发伽马射线发射起源于距离这个“中央引擎”一定距离的喷流,在大多数情况下是快速变化的,具有尖峰和子脉冲的形式。这表明了发动机本身的可变性质,对于这种可变性质,一个合理的机制是吸积流中的内部不稳定性。我们数值求解了中微子冷却环面的结构和演化。我们考虑到微观物理的详细处理,在核物质状态方程,包括中微子捕获效应。模型计算的史瓦西和克尔黑洞。我们发现,对于足够大的吸积率(> 10 Msun/s的非旋转黑洞,和>1 Msun/s的旋转黑洞,取决于它的自旋),盘的内部区域变得不透明,而氦核被光解。该区域压力的突然变化导致粘性和热不稳定性的发展,中微子压力的作用类似于亚爱丁顿盘中的辐射压力。在快速旋转的黑洞的情况下,不稳定性增强,并出现低得多的吸积率。我们还发现了重要的和可能进一步的不稳定的作用,从旋转的黑洞的能量转移到环面通过磁耦合。

英文摘要:

Both types of long and short gamma ray bursts involve a stage of a hyper-Eddington accretion of hot and dense plasma torus onto a newly born black hole. The prompt gamma ray emission originates in jets at some distance from this 'central engine' and in most events is rapidly variable, having a form of spikes and subpulses. This indicates at the variable nature of the engine itself, for which a plausible mechanism is an internal instability in the accreting flow. We solve numerically the structure and evolution of the neutrino-cooled torus. We take into account the detailed treatment of the microphysics in the nuclear equation of state that includes the neutrino trapping effect. The models are calculated for both Schwarzschild and Kerr black holes. We find that for sufficiently large accretion rates (> 10 Msun/s for non-rotating black hole, and >1 Msun/s for rotating black hole, depending on its spin), the inner regions of the disk become opaque, while the helium nuclei are being photodissociated. The sudden change of pressure in this region leads to the development of a viscous and thermal instability, and the neutrino pressure acts similarly to the radiation pressure in sub-Eddington disks. In the case of rapidly rotating black holes, the instability is enhanced and appears for much lower accretion rates. We also find the important and possibly further destabilizing role of the energy transfer from the rotating black hole to the torus via the magnetic coupling.

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