湍流火箭力矩作用下吸积盘和喷流的随机摆动
Stochastic Wobble of Accretion Discs and Jets from Turbulent Rocket Torques
摘要：
吸积盘及其相关外流的模型通常包含轴对称和盘平面对称的假设。然而，对于湍流圆盘，这些对称性仅适用于平均量，而不适用于局部。局部不对称性可引起跨盘中间平面的流出功率的局部不平衡，这又可引起局部倾斜扭矩。在这里，我们计算所产生的随机扭矩盘环的影响，是一个标准的平均场吸积盘模型的后果。扭矩引起垂直于每个平均环平面的矢量的随机游走。这种随机游走的特点是由一个径向依赖的扩散系数，我们计算小角度倾斜。我们使用的系数来计算一个径向依赖的环形倾斜和相关的射流摆动的时间尺度。摆动时间取决于漂移角的平方，因此给定系统的年龄决定了最大摆动角。我们将其应用于耀变体，年轻的恒星物体和双引擎的前行星状星云和微类星体的例子。值得注意的是，对于平均时间为$t_w\sim 3$天，我们估计SS433中喷流的摆动角为$θ\sim 0.8$度，与观测数据不一致。一般来说，随机摆动的非周期性质可以将其与更快的周期性喷流进动区分开来。
英文摘要：
Models of accretion discs and their associated outflows often incorporate assumptions of axisymmetry and symmetry across the disc plane. However, for turbulent discs these symmetries only apply to averaged quantities and do not apply locally. The local asymmetries can induce local imbalances in outflow power across the disc mid-plane, which can in turn induce local tilting torques. Here we calculate the effect of the resulting stochastic torques on disc annuli that are a consequence of standard mean field accretion disc models. The torques induce a random walk of the vector perpendicular to the plane of each averaged annulus. This random walk is characterized by a radially dependent diffusion coefficient which we calculate for small angle tilt. We use the coefficient to calculate a radially dependent time scale for annular tilt and associated jet wobble. The wobble time depends on the square of the wander angle so the age of a given system determines the maximum wobble angle. We apply this to examples of blazars, young stellar objects and binary engines of pre-planetary nebulae and microquasars. It is noteworthy that for an averaging time $t_w\sim 3$ days, we estimate a wobble angle for jets in SS433 of $θ\sim 0.8$ degrees, not inconsistent with observational data. In general the non-periodic nature of the stochastic wobble could distinguish it from faster periodic jet precession.
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