捕获CTA 102 III中的无线电耀斑。核位移与谱分析
Catching the Radio Flare in CTA 102 III. Core-Shift and Spectral Analysis
摘要：
多频、多历元VLBI观测可以研究活动星系核喷流的时空光谱演化。形态和光谱参数的组合可用于导出源固有物理性质，例如磁场和非热粒子密度。在本系列的前两篇论文中，我们分析了blazar CTA 102的单碟光变曲线和VLBI运动学，并提出了一种可能的方案，以解释与2006年耀斑相关的组件的观测演变。在本文中，我们研究的核心移动和光谱的演变，以检验我们的假设，冲击波相互作用。利用8个多频VLBA观测资料，分析了耀斑期间光谱参数的时空演化特征。我们在2005年5月至2007年4月期间使用VLBA在2 - 86 GHz的六个不同频率下观察了CTA 102。在校正VLBA图像的不透明度后，我们进行了详细的光谱分析。从导出的值，我们估计的磁场和相对论粒子的密度。对不透明度变化的详细分析表明，喷流核心的位置与nu^-1成正比，但存在一定的时间变化。该值表明在最致密的区域磁场能量和粒子动能密度之间可能存在均分。从物理参数的变化，我们推断，2006年耀斑在CTA 102连接到一个新的旅行功能（t=2005.9）和这个冲击波和一个静止的结构之间的相互作用，从核心约0.1质量的喷射。震源运动学、频谱和结构变化可以用超压射流中的螺旋运动来描述。
英文摘要：
The temporal and spatial spectral evolution of the jets of AGN can be studied with multi-frequency, multi-epoch VLBI observations. The combination of both, morphological and spectral parameters can be used to derive source intrinsic physical properties such as the magnetic field and the non-thermal particle density. In the first two papers of this series, we analyzed the single-dish light curves and the VLBI kinematics of the blazar CTA 102 and suggested a shock-shock interaction between a traveling and a standing shock wave as a possible scenario to explain the observed evolution of the component associated to the 2006 flare. In this paper we investigate the core-shift and spectral evolution to test our hypothesis of a shock-shock interaction. We used 8 multi-frequency VLBA observations to analyze the temporal and spatial evolution of the spectral parameters during the flare. We observed CTA 102 between May 2005 and April 2007 using the VLBA at six different frequencies spanning from 2 - 86 GHz. After the calibrated VLBA images were corrected for opacity, we performed a detailed spectral analysis. From the derived values we estimated the magnetic field and the density of the relativistic particles. The detailed analysis of the opacity shift reveals that the position of the jet core is proportional to nu^-1 with some temporal variations. The value suggests possible equipartition between magnetic field energy and particle kinetic energy densities at the most compact regions. From the variation of the physical parameters we deduced that the 2006 flare in CTA 102 is connected to the ejection of a new traveling feature (t=2005.9) and the interaction between this shock wave and a stationary structure around 0.1 mas from the core. The source kinematics together with the spectral and structural variations can be described by helical motions in an over-pressured jet.
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