论文标题

来自开普勒积分磁盘I重新检查冲击的MHD喷气机的数值模拟

Numerical simulations of MHD jets from Keplerian accretion disks I-Recollimation shocks

论文作者

Jannaud, Thomas, Zanni, Claudio, Ferreira, Jonathan

论文摘要

目标。我们希望从开普勒积聚磁盘对磁驱动的稳态喷气机之间建立牢固的联系。特别是,后者已经预测了由于主导压力而引起的回忆冲击,到目前为止,在平台模拟中从未观察到。 方法。我们使用Pluto代码对非相对性喷气机进行了一组轴对称MHD模拟。这些模拟旨在重现分析研究中通常预期的边界条件。我们改变了两个参数:磁通量径向指数$α$和喷气质量负载$κ$。为了达到分析溶液所隐含的巨大前所未有的空间量表,已经使用了一种新方法,可以提高时间进化。 结果。我们证实了在大距离内存在站立回归冲击的存在,与自相似研究一样,以质量载荷$κ$的定性行为。冲击很弱,对应于中等高的快速磁通流中的倾斜冲击。从磁盘发射的射流集中在轴向内脊柱上,该脊柱是连接到中央OBJET的流出。该脊柱的存在表明对喷射渐近学具有很大影响。 结论。内部回忆冲击可能会产生可观察到的特征,例如增强发射的站立结和流动速率的降低。但是,更现实的模拟,例如为了研究非轴对称不稳定性并仅从磁盘中的有限区域射出,必须进行完全的三维,以便验证这些MHD回忆冲击是否维持了这些MHD回忆冲击及其性质。

Aims. We wish to establish a firm link between jet simulations and analytical studies of magnetically-driven steady-state jets from Keplerian accretion disks. In particular, the latter have predicted the existence of recollimation shocks due to the dominant hoop-stress, so far never observed in platform simulations. Methods. We perform a set of axisymmetric MHD simulations of non-relativistic jets using the PLUTO code. The simulations are designed to reproduce the boundary conditions generally expected in analytical studies. We vary two parameters: the magnetic flux radial exponent $α$ and the jet mass load $κ$. In order to reach the huge unprecedented spatial scales implied by the analytical solutions, a new method allowing to boost the temporal evolution has been used. Results. We confirm the existence of standing recollimation shocks at large distances, behaving qualitatively with the mass load $κ$ as in self-similar studies. The shocks are weak and correspond to oblique shocks in a moderately high fast-magnetosonic flow. The jet emitted from the disk is focused towards the axial inner spine, which is the outflow connected to the central objet. The presence of this spine is shown to have a strong influence on jet asymptotics. Conclusions. Internal recollimation shocks may produce observable features such as standing knots of enhanced emission and a decrease of the flow rotation rate. However, more realistic simulations, e.g. fully three-dimensional, must be done in order to investigate non-axisymmetric instabilities and with ejection only from a finite zone in the disk, so as to to verify whether these MHD recollimation shocks and their properties are maintained.

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