Revealing the Nature of Blazar Radio Cores through Multifrequency Polarization Observations with the Korean VLBI Network
Revealing the Nature of Blazar Radio Cores through Multifrequency Polarization Observations with the Korean VLBI Network
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DOI：
10.3847/1538-4357/aac490
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发表时间：
2018-05
期刊：
影响因子：
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通讯作者：
Jongho Park;M. Kam;S. Trippe;Sincheol Kang;D. Byun;Dae-Won Kim;J. Algaba;Sang-Sung Lee;
中科院分区：
文献类型：
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作者：
Jongho Park;M. Kam;S. Trippe;Sincheol Kang;D. Byun;Dae-Won Kim;J. Algaba;Sang-Sung Lee;
我们利用韩国 VLBI 网络 (KVN) 在 2016 年底至 2017 年初的三个时期在活跃星系核项目的等离子体物理框架内获得的观测数据，同时研究了 8 个耀变体的无线电核心在 22、43 和 86 GHz 下的线性极化。我们研究了磁芯的法拉第旋转测量（RM）；如果核心位置由于同步加速器自吸收而取决于频率，则 RM 预计会随着观测频率而增加。我们发现，在我们的目标中，观测频率较高时，RM 会系统性增加。 RM-ν 关系遵循幂律，指数分布在 2 附近，表明圆锥形扩展的流出充当法拉第旋转介质。将我们的 KVN 数据与来自 Steward 天文台的几个来源的同期光学偏振数据进行比较，我们发现有迹象表明 RM 随频率的增加在几百吉赫兹的频率处达到饱和。这表明耀变体核心是物理结构而不是简单的 τ = 1 表面。单个区域，例如重准激波，可能主导喷气发射区域下游的喷气发射。我们在大约 1 个月的时间尺度上检测到 CTA 102 观测到的 RM 的符号变化，这可能与其核心出现的新超光速组件经历加速/减速和/或弯曲有关。我们看到类星体的核心 RM 比 BL Lac 天体更高的迹象，这可能是由于类星体的流入/流出更密集。
We study the linear polarization of the radio cores of eight blazars simultaneously at 22, 43, and 86 GHz with observations obtained by the Korean VLBI Network (KVN) in three epochs between late 2016 and early 2017 in the frame of the Plasma-physics of Active Galactic Nuclei project. We investigate the Faraday rotation measure (RM) of the cores; the RM is expected to increase with observing frequency if core positions depend on frequency owing to synchrotron self-absorption. We find a systematic increase of RMs at higher observing frequencies in our targets. The RM–ν relations follow power laws with indices distributed around 2, indicating conically expanding outflows serving as Faraday rotating media. Comparing our KVN data with contemporaneous optical polarization data from the Steward Observatory for a few sources, we find indications that the increase of RM with frequency saturates at frequencies of a few hundred gigahertz. This suggests that blazar cores are physical structures rather than simple τ = 1 surfaces. A single region, e.g., a recollimation shock, might dominate the jet emission downstream of the jet-launching region. We detect a sign change in the observed RMs of CTA 102 on a timescale of ≈1 month, which might be related to new superluminal components emerging from its core undergoing acceleration/deceleration and/or bending. We see indications for quasars having higher core RMs than BL Lac objects, which could be due to denser inflows/outflows in quasars.