Centimeter-Wavelength Total Flux and Linear Polarization Properties of Radio-loud BL Lacertae Objects
Centimeter-Wavelength Total Flux and Linear Polarization Properties of Radio-loud BL Lacertae Objects
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DOI：
10.1086/306799
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发表时间：
1998-10
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影响因子：
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通讯作者：
M. Aller;H. Aller;P. Hughes;G. E. Latimer
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文献类型：
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作者：
M. Aller;H. Aller;P. Hughes;G. E. Latimer
我们目前的结果，从一个长期的计划，以量化的厘米波长的总通量和线性偏振的变化特性的41个无线电大声BL紫胶对象的样本的行为范围，每周到三个月的观测与密歇根大学的26米望远镜在14.5，8.0，和4.8 GHz的;这些观测被用于识别这些BL拉克和皮尔逊-读数头样本中的类星体之间的类相关差异。作为一个群体，BL拉克被发现是更高度可变的总通量密度比类星体。这些变化往往是几乎同时发生的，在14.5和4.8 GHz的幅度相当，这与类星体的行为形成鲜明对比，并支持存在类相关的差异，在秒差距尺度的射流不透明度。通量观测的结构-功能分析量化了特征时间尺度仅在三分之一的BL拉克中是可识别的，并且在大多数程序源中，活动在探测的时间尺度内是不相关的。时间平均分数线性极化仅为百分之几的顺序，并与发射区域内的纠缠磁场的存在是一致的。在许多源中，存在电矢量位置角的优选长期取向。当与非常长的基线干涉结构轴相比，没有首选的位置角的差异被确定;衍生的分布类似于已知的核心组件从非常长的基线偏振测量。极化通量通常表现出几个月到几年的时间尺度的变化，并在几次分解爆发期间表现出传播冲击波的特征。通量和偏振的变化表明，源发射主要是由于不断变化的源组件，并支持发生更频繁的冲击形成BL Lac秒差距尺度流比类星体喷流，其中的磁场拓扑结构，即使在爆发是类似的底层静态流。我们发现BL拉克和类星体在变率行为和极化方面的差异可以用最近的相对论流体动力学研究发现的喷流之间稳定性的差异来解释。
We present results from a long-term program to quantify the range of behavior of the centimeter-wavelength total flux and linear polarization variability properties of a sample of 41 radio-loud BL Lac objects using weekly to trimonthly observations with the University of Michigan 26 m telescope operating at 14.5, 8.0, and 4.8 GHz; these observations are used to identify class-dependent differences between these BL Lacs and QSOs in the Pearson-Readhead sample. As a group, the BL Lacs are found to be more highly variable in total flux density than the QSOs. These changes are often nearly simultaneous and of comparable amplitude at 14.5 and 4.8 GHz, which contrasts with the behavior in the QSOs and supports the existence of class-dependent differences in opacity within the parsec-scale jet flows. Structure-function analyses of the flux observations quantify that a characteristic timescale is identifiable in only one-third of the BL Lacs and that in the majority of the program sources the activity is uncorrelated within the timescales probed. The time-averaged fractional linear polarizations are only on the order of a few percent and are consistent with the presence of tangled magnetic fields within the emitting regions. In many sources a preferred long-term orientation of the electric vector position angle is present. When compared with the very long baseline interferometry structural axis, no preferred position angle difference is identified; the derived distribution resembles that known for core components from very long baseline polarimetry measurements. The polarized flux typically exhibits variability with timescales of months to a few years and exhibits the signature of a propagating shock during several resolved outbursts. The flux and polarization variability indicate that the source emission is predominately due to evolving source components and supports the occurrence of more frequent shock formation in BL Lac parsec-scale flows than in QSO jets, where the magnetic field topology even during outbursts is similar to that of the underlying quiescent flow. The differences that we find in variability behavior and polarization between BL Lacs and QSOs can be explained by differences in stability between the jet flows found by recent studies of relativistic hydrodynamic flows.