MAGNETIC ACCELERATION OF ULTRARELATIVISTIC GRB AND AGN JETS
MAGNETIC ACCELERATION OF ULTRARELATIVISTIC GRB AND AGN JETS
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DOI：
10.1142/s0218271808013285
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发表时间：
2008-01
影响因子：
2.2
通讯作者：
M. Barkov;S. Komissarov
中科院分区：
文献类型：
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作者：
M. Barkov;S. Komissarov
我们提出了冷，轴对称，磁驱动相对论外流的数值模拟。外流最初是亚Alfvenic和坡印廷通量占主导地位，与总静止质量的能量通量比高达μ ~ 620。为了研究喷流的磁加速度，我们模拟了一个漏斗内的流动，漏斗有一个规定形状的刚性壁，我们取它为z ra（在柱坐标系中，a的范围从1到2）。这使我们能够消除数值耗散的影响所引起的自由边界与周围介质。我们发现，在所有情况下，他们收敛到一个稳定的状态，其特征在于由一个空间扩展的加速区域。对于喷流解来说，加速过程非常有效--在模拟的最外尺度上，超过一半的坡印廷通量已转化为动能通量，并且终端洛伦兹因子接近其最大可能值（r ∞ μ）。加速伴随着磁场线的准直，超过了漏斗形状所指示的磁场线。数值解与半解析的自相似喷流解以及在某些天体物理相对论喷流中观测到的空间扩展加速度基本一致。与之前的研究一致，我们还发现加速度对于风解的有效性显着降低，这表明脉冲星风在到达终止激波时可能仍保持坡印廷主导。
We present numerical simulations of cold, axisymmetric, magnetically driven relativistic outflows. The outflows are initially sub-Alfvenic and Poynting-flux dominated, with total–to–rest-mass energy flux ratio up to μ ~ 620. To study the magnetic acceleration of jets we simulate flows confined within a funnel with a rigid wall of prescribed shape, which we take to be z ∝ ra (in cylindrical coordinates, with a ranging from 1 to 2). This allows us to eliminate the numerical dissipative effects induced by a free boundary with an ambient medium. We find that in all cases they converge to a steady state characterized by a spatially extended acceleration region. For the jet solutions the acceleration process is very efficient — on the outermost scale of the simulation more than half of the Poynting flux has been converted into kinetic energy flux, and the terminal Lorentz factor approached its maximum possible value (Γ∞ ≃ μ). The acceleration is accompanied by the collimation of magnetic field lines in excess of that dictated by the funnel shape. The numerical solutions are generally consistent with the semi-analytic self-similar jets solutions and the spatially extended acceleration observed in some astrophysical relativistic jets. In agreement with previous studies, we also find that the acceleration is significantly less effective for wind solutions suggesting that pulsar winds may remain Poynting dominated when they reach the termination shock.