Realization of a multifrequency celestial reference frame through a combination of normal equation systems

TL;DR

This paper develops a precise, multifrequency celestial reference frame by combining radio source catalogs from VLBI observations over 40 years, using a novel covariance-preserving method, resulting in a highly accurate and validated catalog aligned with ICRF3.

Contribution

It introduces a new combination approach that preserves full covariance information across catalogs, improving the accuracy and consistency of the celestial reference frame.

Findings

The final catalog contains 4617 sources with high positional accuracy.

The combined frame aligns with ICRF3 within 3 microarcseconds.

Significant differences observed when comparing with Gaia-CRF.

Abstract

Context. We present a celestial reference frame (CRF) based on the combination of independent, multifrequency radio source position catalogs using nearly 40 years of Very Long Baseline Interferometry observations at the standard geodetic frequencies at SX band and about 15 years of observations at higher frequencies (K and XKa). The final catalog contains 4617 sources. Aims. We produce a multifrequency catalog of radio source positions with full variance-covariance information across all radio source positions of all input catalogs. Methods. We combined three catalogs, one observed at 8 GHz (X band), one at 24 GHz (K band) and one at 32 GHz (Ka band). Rather than only using the radio source positions, we developed a new, rigorous combination approach by carrying over the full covariance information through the process of adding normal equation systems. Special validation routines were used to characterize the random and systematic errors between the input reference frames and the combined catalog. Results. The resulting CRF contains precise positions of 4617 compact radio astronomical objects, 4536 measured at 8 Ghz, 824 sources also observed at 24 GHz, and 674 at 32 GHz. The frame is aligned with ICRF3 within 3 $\mu$as and shows an average positional uncertainty of 0.1 mas in right ascension and declination. No significant deformations can be identified. Comparisons with Gaia-CRF remain inconclusive, nonetheless significant differences between all frames can be attested.