Consistency and precision of very long baseline interferometry source coordinate time series

Abstract

Context. Coordinate time series of extragalactic radio sources produced by different analysis centers from very long baseline interferometry observations are widely used to evaluate source positional stability, select stable sources for celestial reference frames, assess the stability of reference-frame axes, and investigate source-related astrometric variability. The external consistency and realistic errors of these time-series products, as well as their relation to processing strategies and analysis configurations, remain to be further investigated. Aims. We aim to compare source coordinate time-series solutions from different analysis centers and investigate how processing strategies and configurations contribute to their differences. Methods. We collected eight coordinate time-series solutions from seven analysis centers and constructed a final sample of 496 common sources after data selection, reference-frame alignment, and the extraction of common observing sessions. The inter-solution differences were characterized using pairwise positional offsets and correlation analysis. The positional realistic errors of each solution were estimated with the N-cornered-hat (NCH) method and bootstrap resampling. Results. For most solutions, the median weighted root mean square (WRMS) values of the coordinate time-series solutions are at the level of a few hundred micro-arc seconds (μas), and the median NCH-derived precision is approximately 200–300 μas in right ascension and 250–400 μas in declination. Solutions with similar processing strategies, software packages, or source constraints typically show higher inter-solution consistency, as reflected by more similar WRMS values, stronger correlations, and closer NCH-derived precision estimates. The consistency among solutions is therefore affected not only by the broad distinction between global and independent modes but also by the detailed analysis configuration. The NCH-derived precision shows a clear dependence on source declination, with poorer precision in the southern sky, and becomes more stable for sources with a larger number of observing sessions. Conclusions. Different processing strategies and analysis configurations introduce marginal differences, while the source coordinate time-series solutions generally remain consistent. Inter-solution comparisons provide an independent way to obtain a realistic estimate of the stochastic errors of these products beyond their formal errors.