A new approach to the assessment of stochastic errors of radio source position catalogues

摘要

Assessing the external stochastic errors of radio source position cataloguesderived from VLBI observations is important for tasks such as estimating thequality of the catalogues and their weighting during combination. One of thewidely used methods to estimate these errors is the three-cornered-hattechnique, which can be extended to the N-cornered-hat technique. A criticalpoint of this method is how to properly account for the correlations betweenthe compared catalogues. We present a new approach to solving this problem thatis suitable for simultaneous investigations of several catalogues. To computethe correlation between two catalogues $A$ and $B$, the differences betweenthese catalogues and a third arbitrary catalogue $C$ are computed. Then thecorrelation between these differences is considered as an estimate of thecorrelation between catalogues $A$ and $B$. The average value of theseestimates over all catalogues $C$ is taken as a final estimate of the targetcorrelation. In this way, an exhaustive search of all possible combinationsallows one to compute the paired correlations between all catalogues. As anadditional refinement of the method, we introduce the concept of weightedcorrelation coefficient. This technique was applied to nine recently publishedradio source position catalogues. We found large systematic differences betweencatalogues, that significantly impact determination of their stochastic errors.Finally, we estimated the stochastic errors of the nine catalogues.