标题： HESS J1943+213：一个非经典高频率峰值BL Lac天体 显示英文标题

标题： HESS J1943+213: a non-classical high-frequency-peaked BL Lac object

摘要： HESS J1943+213是一个未被识别的TeV源，很可能是一个高频率峰值BL Lac（HBL）天体，但也与脉冲星风星云（PWN）性质相容。这些截然不同的天文学解释都得到了一些观测到的异常特征的支持。为了最终对该天体进行分类和理解，我们采取了三种方法，通过时域、高角分辨率和多频率射电研究。首先，我们使用阿雷西博望远镜进行的深度时域观测未能发现可能为所提议的PWN提供能量的脉冲星。我们以约70%的确定性得出结论，HESS J1943+213不包含脉冲星。其次，使用e-MERLIN在1.5-和5-GHz频率下对源进行长基线干涉测量，仅显示出一个核心，即在~1 - 100毫角秒分辨率下的点源。其2013年的流量密度比2011年类似分辨率观测中检测到的低约三分之一。核心的射电变化加强了HBL天体假说。第三，来自我们编译的射电谱的更多证据反对PWN情景。扩展结构遵循幂律行为，光谱指数alpha = -0.54 +- 0.04，而核心成分是平坦谱（alpha = -0.03 +- 0.03）。相反，PWNe的射电同步辐射发射预测一个单一的幂律分布。总体而言，我们排除了PWN假说，并得出结论该源是一个BL Lac天体。从扩展结构中持续的高流量密度比例（70%）则使我们得出结论，HESS J1943+213必须是一个非经典的HBL天体。 显示英文摘要

摘要： HESS J1943+213 is an unidentified TeV source that is likely a high-frequency-peaked BL Lac (HBL) object but also compatible with a pulsar wind nebula (PWN) nature. Each of these enormously different astronomical interpretations is supported by some of the observed unusual characteristics. In order to finally classify and understand this object we took a three-pronged approach, through time-domain, high angular resolution, and multi-frequency radio studies. First, our deep time-domain observations with the Arecibo telescope failed to uncover the putative pulsar powering the proposed PWN. We conclude with ~70% certainty that HESS J1943+213 does not host a pulsar. Second, long-baseline interferometry of the source with e-MERLIN at 1.5- and 5- GHz, shows only a core, a point source at ~ 1 - 100 milli-arcsecond resolution. Its 2013 flux density is about one-third lower than detected in 2011 observations with similar resolution. This radio variability of the core strengthens the HBL object hypothesis. More evidence against the PWN scenario comes, third, from the radio spectrum we compiled. The extended structure follows a power-law behavior with spectral index alpha = -0.54 +- 0.04 while the core component is flat spectrum (alpha = -0.03 +- 0.03). In contrast, the radio synchrotron emission of PWNe predicts a single power-law distribution. Overall we rule out the PWN hypothesis and conclude the source is a BL Lac object. The consistently high fraction (70%) of the flux density from the extended structure then leads us to conclude that HESS J1943+213 must be a non-classical HBL object.