Evolution of the radio source position uncertainties in radio astrometric catalogs over the past three decades

TL;DR

This study analyzes three decades of radio astrometric catalogs, showing significant improvements in source position uncertainties due to increased observations, with uncertainties decreasing by an order of magnitude and following power law trends.

Contribution

It provides a comprehensive analysis of the evolution of radio source position uncertainties and identifies the number of observations as the key factor in improvements.

Findings

Median source position uncertainty decreased from 0.156 mas to 0.015 mas.

Number of observations increased from 1.3 to 14.4 million, following a power law.

Position uncertainty improvement correlates strongly with the number of observations.

Abstract

In this paper, progress in improving the coordinates uncertainty of extragalactic radio sources derived from astrometric and geodetic VLBI observations is investigated. For this purpose, 30 catalogs of radio source positions computed in 1997-2025 were analyzed. Over these years, the median source position uncertainty represented by the semi-major axis of the error ellipse for 467 sources in common to all catalogs improved by one order of magnitude: from 0.156 mas to 0.015 mas. It was also found that the improvement in the position uncertainty over time follows a power law with high accuracy. The number of observations used for determination of the coordinates of the common sources in the input catalogs increased over time from 1.3 to 14.4 million, also following a power law. A discussion of the results led us to the conclusion that the number of observations is the primary factor in improving the source positions uncertainty compared to the number of sessions in which the source was observed.