利用具备甚长基线干涉测量（VLBI）探测到反向喷流的活动星系核（AGN）的变异性和自行测量宇宙学距离的改进方法
A refined method for measuring cosmological distances using variability and proper motions in AGN with VLBI-detected counter-jets
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中文总结 AI 辅助
该研究改进了利用AGN射电变异性的标准测速枪距离法，通过VLBI探测到的喷流与反向喷流自行消除了对多普勒因子的依赖，得到3C 84的角直径距离，结果与不同宇宙学模型的预期相符。
中文摘要 AI 辅助
在之前的一篇论文中，我们描述了一种“标准测速枪”（SSG）距离测量方法，该方法基于耀变体的射电变异性受因果限制的假设，利用光速来标准化标尺，随后通过甚长基线干涉测量（VLBI）测量视大小，进而推导角直径距离。该方法的一个关键局限是需要知晓相对论性多普勒因子。此前，我们假设多普勒因子δ≈1，估算了英仙座星系团中心明亮射电源3C 84的距离。在本文中，我们旨在说明如何利用探测到的反向喷流与前向喷流的自行，来消除这种距离测量方法对多普勒因子的依赖。在假设发射区为盘状（或球状）几何结构，并通过因果校正因子（κ）参数化物理发射区与变时标的关系的前提下，我们估算了3C 84（红移z=0.0178）的改进角直径距离及其统计误差。假设κ=1，我们得到盘状几何下的距离D_A,disk=78.9(-9.8+11.0)Mpc，球状几何下的距离D_A,sphere=71.2(-8.8+9.7)Mpc。将这些结果与文献基准对比后发现，球状假设得到的距离与经SH0ES哈勃常数（H0）校准的本地Ia型超新星结果一致，而盘状几何假设则与低H0宇宙学的预期相符。最终，这表明利用喷流与反向喷流的运动学特性，成功消除了标准测速枪方法对多普勒因子的依赖，一旦明确喷流的几何结构，就能提供一种可行的独立距离估算方式。
英文摘要
In a previous paper, we described a `standard speed-gun' (SSG) distance that uses the speed of light to standardize a ruler under the assumption that the radio variability seen in blazars is causally limited. The apparent size is then measured with Very Long Baseline Interferometry in order to derive the angular diameter distance. A key limitation of this method is that it requires knowledge of the relativistic Doppler factor. Previously, we estimated the distance to the bright radio source, 3C 84 at the center of the Perseus cluster assuming a Doppler factor of δ~ 1. In this paper, we aim to describe how a detected counter-jet and approaching jet proper motions can be used to remove the need for knowledge of the Doppler factor when measuring cosmological distances in this way. Under the assumption of a disk (or spherical) geometry and parameterizing the relationship between the physical emitting region and the variability timescale via a causality correction factor (kappa), we estimate a refined angular diameter distance to 3C 84 (z=0.0178) with statistical errors. Assuming kappa=1, we derive distances of D_A,disk = 78.9(-9.8+11.0) Mpc (or D_A,sphere = 71.2(-8.8+9.7) Mpc). Comparing these results to literature benchmarks, we find that the spherical assumption yields a distance consistent with local Type Ia supernovae calibrated to the SH0ES H0, while a disk-like geometry aligns with expectations from a lower H0 cosmology. Ultimately, this demonstrates that utilizing jet and counter-jet kinematics successfully removes the Doppler-factor dependence from the standard speed-gun method, providing a viable independent distance estimate once the geometric structure of the jet is resolved.
