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arXiv 1209.4707astro-ph.HE
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低吸积率下黑洞相对论喷流的发射和熄灭

Launching and Quenching of Black Hole Relativistic Jets at Low Accretion Rate

Hung-Yi Pu, Kouichi Hirotani, Hsiang-Kuang Chang

摘要:

相对论喷流是从黑洞(BH)X射线双星和活动星系核中发射的,当盘吸积率低于某个极限时(即,当吸积速率与Eddingtion吸积速率之比$\dot{m}$低于约0.01时),但当高于约0.01时淬灭。我们提出了一个新的范式来解释这种观察到的喷流和吸积盘之间的耦合,通过调查提取的旋转能量的BH时,它被包围在不同类型的吸积盘。在低吸积速率(例如,当$\dot{m}\lesssim0.1$)时,在事件视界附近的吸积是准球形的。吸积等离子体落在大范围纬度的事件视界上,打破了视界附近的无力近似。为了考虑等离子体惯性效应,我们考虑了磁流体动力学(MHD)提取旋转能量从BH的吸积MHD流体,所描述的MHD彭罗斯过程。研究发现,当吸积盘由外部的Shakura-Sunyaev盘(SSD)和内部的对流主导的吸积流组成时,吸积盘的能量提取起作用,从而产生相对论性喷流.当整个吸积盘类型转变为SSD时,由于等离子体带来的静止质量能量大于电磁从空穴中提取的能量,从而停止提取,因此喷流被淬灭。其他几个观察到的BH盘喷流耦合,如为什么无线电光度增加,增加X射线光度,直到无线电发射下降,也得到了解释。

英文摘要:

Relativistic jets are launched from black hole (BH) X-ray binaries and active galactic nuclei when the disk accretion rate is below a certain limit (i.e., when the ratio of the accretion rate to the Eddingtion accretion rate, $\dot{m}$, is below about 0.01) but quenched when above. We propose a new paradigm to explain this observed coupling between the jet and the accretion disk by investigating the extraction of the rotational energy of a BH when it is surrounded by different types of accretion disk. At low accretion rates (e.g., when $\dot{m}\lesssim0.1$), the accretion near the event horizon is quasi-spherical. The accreting plasmas fall onto the event horizon in a wide range of latitudes, breaking down the force-free approximation near the horizon. To incorporate the plasma inertia effect, we consider the magnetohydrodynamical (MHD) extraction of the rotational energy from BHs by the accreting MHD fluid, as described by the MHD Penrose process. It is found that the energy extraction operates, and hence a relativistic jet is launched, preferentially when the accretion disk consists of an outer Shakura-Sunyaev disk (SSD) and an inner advection-dominated accretion flow. When the entire accretion disk type changes into an SSD, the jet is quenched because the plasmas brings more rest-mass energy than what is extracted from the hole electromagnetically to stop the extraction. Several other observed BH disk-jet couplings, such as why the radio luminosity increases with increasing X-ray luminosity until the radio emission drops, are also explained.

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