MOJAVE. X. PARSEC-SCALE JET ORIENTATION VARIATIONS AND SUPERLUMINAL MOTION IN ACTIVE GALACTIC NUCLEI
MOJAVE. X. PARSEC-SCALE JET ORIENTATION VARIATIONS AND SUPERLUMINAL MOTION IN ACTIVE GALACTIC NUCLEI
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DOI：
10.1088/0004-6256/146/5/120
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发表时间：
2013-08
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通讯作者：
M. Lister;M. Aller;H. Aller;D. Homan;K. Kellermann;Y. Kovalev;Y. Kovalev;A. Pushkarev;A. Pushkare
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作者：
M. Lister;M. Aller;H. Aller;D. Homan;K. Kellermann;Y. Kovalev;Y. Kovalev;A. Pushkarev;A. Pushkare
基于1994年8月31日至2011年5月1日期间获得的15 GHz甚长基线阵列（VLBA）数据，我们描述了200个活动星系核（AGN）喷流的秒差距尺度运动学。我们提出了新的VLBA 15 GHz的图像，这些和59个额外的活动星系核的莫哈韦和2厘米的调查计划。几乎所有60个观测最多的喷流在12-16年的时间间隔内，其最内侧位置角都有显著的变化，在天空上的变化范围从10°到150°，对应的内在变化范围为0.5 °到0.2 °。BL Lac喷流的变化比类星体小。大约一半的大量观察到的射流显示系统的位置角随时间的趋势，和20个显示振荡行为的迹象。然而，与拟合周期（5-12年）相比，数据集的时间跨度太短，无法可靠地确定周期性。在许多情况下看到的位置角的快速变化和大的跳跃表明，超光速活动星系核喷流的功能只占整个喷流横截面的一部分，并可能在喷流内薄的不稳定结构的通电部分。我们推导出矢量自行887移动功能在200个喷气机至少有五个VLBA时代。对于557个良好采样的特征，有足够的数据来进一步研究可能的加速度。我们发现，移动的功能一般是非弹道，与70%的良好采样的功能显示出显着的加速度或非径向运动。向内运动很少见（占所有特征的2%），速度很慢（<0.1 mas yr-1），在BL Lac喷流中更为普遍，并且通常在未解决的核心特征的1 mas范围内发现。射电星系和BL Lac天体的表观速度都有随着距离的增加而增加的趋势。在大多数射流中，特征的速度聚集在特征值周围，但分布中存在相当大的分散性。射流内的取向变化不能完全解释色散，这意味着特征具有洛伦兹因子和/或图案速度的范围。非常慢的模式速度特征是罕见的，仅占样本的4%，并且在射电星系和BL Lac喷流中更为普遍。我们证实了以前报道的上包络线的速度与光束亮度的移动射流功能的分布。在1026 W Hz−1以下，随着15 GHz射电光度的降低，最大速度会下降。包络线的一般形状意味着，本质上最强大的活动星系核喷流有一个范围很广的洛伦兹因子，最高可达1040，而本质上较弱的喷流只有轻微的相对论性。
We describe the parsec-scale kinematics of 200 active galactic nucleus (AGN) jets based on 15 GHz Very Long Baseline Array (VLBA) data obtained between 1994 August 31 and 2011 May 1. We present new VLBA 15 GHz images of these and 59 additional AGNs from the MOJAVE and 2 cm Survey programs. Nearly all of the 60 most heavily observed jets show significant changes in their innermost position angle over a 12–16 yr interval, ranging from 10° to 150° on the sky, corresponding to intrinsic variations of ∼0.°5 to ∼2°. The BL Lac jets show smaller variations than quasars. Roughly half of the heavily observed jets show systematic position angle trends with time, and 20 show indications of oscillatory behavior. The time spans of the data sets are too short compared to the fitted periods (5–12 yr), however, to reliably establish periodicity. The rapid changes and large jumps in position angle seen in many cases suggest that the superluminal AGN jet features occupy only a portion of the entire jet cross section and may be energized portions of thin instability structures within the jet. We have derived vector proper motions for 887 moving features in 200 jets having at least five VLBA epochs. For 557 well-sampled features, there are sufficient data to additionally study possible accelerations. We find that the moving features are generally non-ballistic, with 70% of the well-sampled features showing either significant accelerations or non-radial motions. Inward motions are rare (2% of all features), are slow (<0.1 mas yr−1), are more prevalent in BL Lac jets, and are typically found within 1 mas of the unresolved core feature. There is a general trend of increasing apparent speed with distance down the jet for both radio galaxies and BL Lac objects. In most jets, the speeds of the features cluster around a characteristic value, yet there is a considerable dispersion in the distribution. Orientation variations within the jet cannot fully account for the dispersion, implying that the features have a range of Lorentz factor and/or pattern speed. Very slow pattern speed features are rare, comprising only 4% of the sample, and are more prevalent in radio galaxy and BL Lac jets. We confirm a previously reported upper envelope to the distribution of speed versus beamed luminosity for moving jet features. Below 1026 W Hz−1 there is a fall-off in maximum speed with decreasing 15 GHz radio luminosity. The general shape of the envelope implies that the most intrinsically powerful AGN jets have a wide range of Lorentz factors up to ∼40, while intrinsically weak jets are only mildly relativistic.