一种估计VLBI喷流成分抛射历元的概率方法及其在MOJAVE 15 GHz VLBA运动学中的应用
A Probabilistic Method for Estimating VLBI Jet-Component Ejection Epochs. Application to MOJAVE 15 GHz VLBA Kinematics
- Max-Planck-Institut für Radioastronomie（马克斯·普朗克射电天文研究所）
- Department of Physics and Astronomy, Denison University（丹尼森大学物理与天文学系）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
提出一种概率框架，通过蒙特卡洛传播轨迹不确定性并校准有效核心区域，估计VLBI喷流成分抛射历元，应用于MOJAVE样本得到1589个历元，有效样本量提升至传统方法的2.8倍。
AI中文摘要：
活动星系核（AGN）中秒差距尺度喷流成分的抛射历元通常通过将拟合轨迹外推回VLBI核心来估计，这些成分由甚长基线干涉测量（VLBI）追踪。然而，轨迹不确定性、非径向运动、加速度以及核心的有限尺寸和位置变化可能使此类估计变得不确定，并限制可用样本。我们开发了一个概率框架，用于估计VLBI成分的抛射历元（包括加速特征），并量化每条向后外推轨迹与有效VLBI核心区域相关联的一致性程度。我们将该框架应用于15 GHz MOJAVE运动学样本中的1923条喷流成分轨迹。抛射历元定义为外推轨迹最接近核心的时间，轨迹不确定性通过蒙特卡洛采样传播。有效核心半径被视为一个随机变量，其总体尺度根据最接近位置分布进行校准。随后，每个成分被赋予一个依赖于模型的概率，表示其最接近位置位于该有效核心区域内的可能性。该方法得到1589个抛射历元。拟合的有效核心区域尺度为$\sigma_{\rm c}=0.16\pm0.02$毫角秒，对应平均核心半径为$0.20\pm0.03$毫角秒，并给出垂直于喷流方向的15 GHz特征核心漂移的总体上限为$\lesssim0.16$毫角秒。使用相同的概率加权，完整概率样本的有效数量为$N_{\rm eff}=624$，是传统MOJAVE值222的2.8倍，而重叠的抛射历元与先前估计保持一致。该框架为喷流结构演化和AGN变异的群体研究及互相关分析提供了灵活基础。
英文摘要：
Ejection epochs of parsec-scale jet components in active galactic nuclei (AGN), tracked with Very Long Baseline Interferometry (VLBI), are commonly estimated by extrapolating fitted trajectories back to the VLBI core. However, trajectory uncertainties, non-radial motion, acceleration, and the finite size and position variability of the core can make such estimates uncertain and restrict usable samples. We develop a probabilistic framework for estimating VLBI-component ejection epochs, including accelerated features, and for quantifying how consistently each backward-extrapolated trajectory is associated with an effective VLBI core region. We apply the framework to 1923 jet-component trajectories from the 15 GHz MOJAVE kinematic sample. Ejection epochs are defined as the times of closest approach of the extrapolated trajectories to the core, with trajectory uncertainties propagated through Monte Carlo sampling. The effective core radius is treated as a random variable, whose population-level scale is calibrated from the distribution of closest-approach positions. Each component is then assigned a model-dependent probability that its closest approach lies within this effective core region. The method yields 1589 ejection epochs. The fitted effective core-region scale is $σ_{\rm c}=0.16\pm0.02$ mas, corresponding to an average core radius of $0.20\pm0.03$ mas, and gives a population-level upper limit of $\lesssim0.16$ mas on the characteristic 15 GHz core wander perpendicular to the jet. Using the same probability weighting, the full probabilistic sample has $N_{\rm eff}=624$, 2.8 times the legacy MOJAVE value of 222, while the overlapping ejection epochs remain consistent with previous estimates. The framework provides a flexible basis for population studies and cross-correlation analyses of jet structural evolution and AGN variability.
