用第一批GMVA + ALMA观测揭示PDKEEPAAA 287内部喷流结构
Unravelling the Innermost Jet Structure of OJ 287 with the First GMVA+ALMA Observations
摘要：
我们介绍了2017年4月2日与全球毫米VLBI阵列（GMVA）和3.5毫米的相控阿塔卡玛大型毫米/亚毫米阵列（ALMA）联合进行的blazar OJ 287的第一个甚长基线干涉（VLBI）观测。相位ALMA的参与不仅使GMVA南北分辨率提高了约3倍，而且还使条纹探测在基线长于2 Gλ时的信噪比达到300。高灵敏度促使我们用新开发的正则化极大似然成像方法对数据进行成像，以前所未有的高角分辨率揭示最内部的喷流结构。我们的图像显示了一个紧凑的和扭曲的喷流沿西北方向延伸，在内部200 μas内有两个弯曲，类似于一个旋进喷流的投影。东南端的组分具有致密的结构和较高的亮温，被认为是VLBI核。位于地核西北约200 μas处的扩展喷流特征在总强度和线偏振强度上均呈圆锥形，线偏振电矢量位置角呈双峰分布。我们讨论了这一特点的性质，通过比较我们的观察与模型和模拟的斜激波和准直激波与各种磁场配置。我们的高保真图像还使我们能够从次级超大质量黑洞（SMBH）中寻找可能的喷流特征，并测试为该来源提出的SMBH二元假设。
英文摘要：
We present the first very-long-baseline interferometric (VLBI) observations of the blazar OJ287 carried out jointly with the Global Millimeter VLBI Array (GMVA) and the phased Atacama Large Millimeter/submillimeter Array (ALMA) at 3.5 mm on April 2, 2017. Participation of phased-ALMA not only has improved the GMVA north-south resolution by a factor of ~3, but also has enabled fringe detection with signal-to-noise ratios up to 300 at baselines longer than 2 Gλ. The high sensitivity has motivated us to image the data with the newly developed regularized maximum likelihood imaging methods, revealing the innermost jet structure with unprecedentedly high angular resolution. Our images reveal a compact and twisted jet extending along the northwest direction with two bends within the inner 200 μas that resembles a precessing jet in projection. The component at the southeastern end shows a compact morphology and high brightness temperature, and is identified as the VLBI core. An extended jet feature that lies at ~200 μas northwest of the core shows a conical shape in both total and linearly polarized intensity, and a bimodal distribution of the linear polarization electric vector position angle. We discuss the nature of this feature by comparing our observations with models and simulations of oblique and recollimation shocks with various magnetic field configurations. Our high-fidelity images also enabled us to search for possible jet features from the secondary supermassive black hole (SMBH) and test the SMBH binary hypothesis proposed for this source.
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