论文标题

用径向速度剪切的相对论电流的磁力

Magnetization of Relativistic Current-Carrying Jets with Radial Velocity Shear

论文作者

Król, Dominika Ł., Stawarz, Łukasz, Begelman, Mitchell C., Martí, José-María, Perucho, Manel, Petrenko, Bohdan A.

论文摘要

天体物理喷头是从积聚黑洞附近发射的,以射流颗粒和电磁通量的大量动能形式携带大量功率。在这里,我们考虑了一个简单的分析模型,用于在距离发射部位较大距离处的相对论喷气机,假设具有径向速度剪切的圆柱形轴对称几何形状,并且纯粹是环形磁场。我们认为,只要射流等离子体处于磁液压平衡状态,这种流出往往会以粒子为主,即电磁与粒子能量的比率,在射流横截面区域集成,通常低于统一以下,$σ<1 $。同时,对于特定的磁性和径向速度曲线,磁压在某些射流半径范围内仍可能在颗粒压力上占主导地位,即局部喷气等离子体参数$β_{pl} <1 $,这可能与此类系统中高增强发射的粒子加速度和产生相关。射流磁化参数只能将其提升到适度的值$σ\ Lessim \ Mathcal {O}(10)$仅在气压中极端梯度或不连续性的情况下,并且速度剪切速度受到了显着抑制。这样的配置由狭窄的,不磁的喷气脊柱组成,该脊柱被扩展的,无力的层包围,可能需要额外的poloidal场分量来稳定它们,以在电流驱动的振荡下稳定下来,但即使这也不会大大提升其$σ$参数。

Astrophysical jets, launched from the immediate vicinity of accreting black holes, carry away large amounts of power in a form of bulk kinetic energy of jet particles and electromagnetic flux. Here we consider a simple analytical model for relativistic jets at larger distances from their launching sites, assuming a cylindrical axisymmetric geometry with a radial velocity shear, and purely toroidal magnetic field. We argue that, as long as the jet plasma is in magnetohydrostatic equilibrium, such outflows tend to be particle dominated, i.e. the ratio of the electromagnetic to particle energy flux, integrated over the jet cross-sectional area, is typically below unity, $σ< 1$. At the same time, for particular magnetic and radial velocity profiles, magnetic pressure may still dominate over particle pressure for certain ranges of the jet radius, i.e. the local jet plasma parameter $β_{pl} < 1$, and this may be relevant in the context of particle acceleration and production of high-energy emission in such systems. The jet magnetization parameter can be elevated up to the modest values $σ\lesssim \mathcal{O}(10)$ only in the case of extreme gradients or discontinuities in the gaseous pressure, and a significantly suppressed velocity shear. Such configurations, which consist of a narrow, unmagnetized jet spine surrounded by an extended, force-free layer, may require an additional poloidal field component to stabilize them against current-driven oscillations, but even this will not elevate substantially their $σ$ parameter.

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