MOJAVE：使用VLBA实验监测AGN中的射流。VII。Blazar喷气加速
MOJAVE: Monitoring of Jets in AGN with VLBA Experiments. VII. Blazar Jet Acceleration
摘要：
我们讨论了大样本的河外射电喷流的MOJAVE计划，研究秒差距尺度的喷流结构和运动学的一个完整的，通量密度有限的样本活动星系核（AGN）的加速度测量。加速度是从单个射流特征或“组件”的表观运动中测量的，这些特征或“组件”可以代表射流中的模式。我们发现，显着的加速度是共同的平行和垂直于所观察到的分量速度。表示视速度变化的平行加速度通常大于表示视方向变化的垂直加速度。更大的平行加速度的趋势表明，这些表观速度的变化中有很大一部分是由于部件的固有速度变化而不是视线方向的变化。我们发现一个整体的趋势，增加表观速度的组件更接近他们的射流比组件的表观速度下降的基础。这表明观测到的模式运动和底层流动之间存在联系，在某些情况下，底层流动可能在靠近底部的地方速度增加，而在更远的地方速度降低;然而，传播激波的常见流体动力学过程也可能发挥作用。大约一半的部件显示出“非径向”运动，或者部件的结构位置角与其速度方向之间的不对准，并且这些不对准通常更好地将部件运动与下游发射对准。周向加速度与非径向运动密切相关。当一起观察时，垂直加速度通常在正确的方向上，导致观察到的不对准。
英文摘要：
We discuss acceleration measurements for a large sample of extragalactic radio jets from the MOJAVE program which studies the parsec-scale jet structure and kinematics of a complete, flux-density-limited sample of Active Galactic Nuclei (AGN). Accelerations are measured from the apparent motion of individual jet features or "components" which may represent patterns in the jet flow. We find that significant accelerations are common both parallel and perpendicular to the observed component velocities. Parallel accelerations, representing changes in apparent speed, are generally larger than perpendicular acceleration that represent changes in apparent direction. The trend for larger parallel accelerations indicates that a significant fraction of these changes in apparent speed are due to changes in intrinsic speed of the component rather than changes in direction to the line of sight. We find an overall tendency for components with increasing apparent speed to be closer to the base of their jets than components with decreasing apparent speed. This suggests a link between the observed pattern motions and the underlying flow which, in some cases, may increase in speed close to the base and decrease in speed further out; however, common hydro-dynamical processes for propagating shocks may also play a role. About half of the components show "non-radial" motion, or a misalignment between the component's structural position angle and its velocity direction, and these misalignments generally better align the component motion with the downstream emission. Perpendicular accelerations are closely linked with non-radial motion. When observed together, perpendicular accelerations are usually in the correct direction to have caused the observed misalignment.
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