论文标题
vlbi测量的偏差，对AGN射流的核心移位效应
A bias in VLBI measurements of the core shift effect in AGN jets
论文作者
论文摘要
AGN喷气机的Blandford和Königl模型预测，明显不透明喷气基础的位置 - 核心 - 随频率而变化。通过无线电干涉法观察到这种效果，并广泛用于推断最内向喷气区域的参数和结构。通常，通过将高斯模板拟合到干涉可见性来估计无线电芯的位置。这会导致模型近似误差，即可以通过使用现实的喷气模型的观测值模拟来检测和评估的偏差。为了评估偏见，我们基于根据来自真实VLBI通量密度有限的样品的参数的网格进行评估的AGN喷气模型构建人工样本，并在2.3、8.1和15.4 GHz时创建模拟的VLBI数据集。我们发现，核心位置从真正的喷气顶点转移通常被高估了。偏置通常与核心移动随机误差相当，并且对于具有较大明显开口角的喷射器可能达到两个因子。这种观察偏置主要取决于真实核心移位与图像分辨率之间的比率。这意味着磁场，核心径向距离和从核心移位测量值推断的射流速度被高估了。我们提出了一种解决偏见的方法。
The Blandford and Königl model of AGN jets predicts that the position of the apparent opaque jet base - the core - changes with frequency. This effect is observed with radio interferometry and is widely used to infer parameters and structure of the innermost jet regions. The position of the radio core is typically estimated by fitting a Gaussian template to the interferometric visibilities. This results in a model approximation error, i.e. a bias that can be detected and evaluated through simulations of observations with a realistic jet model. To assess the bias, we construct an artificial sample of sources based on the AGN jet model evaluated on a grid of the parameters derived from a real VLBI flux-density-limited sample and create simulated VLBI data sets at 2.3, 8.1 and 15.4 GHz. We found that the core position shifts from the true jet apex are generally overestimated. The bias is typically comparable to the core shift random error and can reach a factor of two for jets with large apparent opening angles. This observational bias depends mostly on the ratio between the true core shift and the image resolution. This implies that the magnetic field, the core radial distance and the jet speed inferred from the core shift measurements are overestimated. We present a method to account for the bias.
