Analysis Strategies for the Densification of the ICRF with VLBA Calibrator Survey Sources
Six campaigns with a total of twenty-four Very Long Baseline Array Calibrator Survey (VCS) observing sessions were carried out with ten radio telescopes located on U.S. territory from 1994 to 2007. The aim of those astrometric sessions was to estimate source positions and to make snapshot images of compact radio sources. Coordinates of about two thirds of the sources in the ICRF2 catalogue are estimated from VCS sessions, most of them from two scans in one session only. Moreover, there are systematic errors due to the deficiencies of a continent-wide network for the estimation of Earth orientation parameters (EOP) and the linking between the celestial and terrestrial frame. We investigate the impact of EOP estimation on source positions for those sessions and we use polar motion estimates from the analysis of Global Navigation Satellite Systems (GNSS) observations to strengthen the solution. We find that there is a systematic effect up to 1 mas in the estimated source coordinates between a solution with fixed EOP coming from the GNSS techniques and a solution where the EOP are estimated in the Very Long Baseline Interferometry analysis. Furthermore, we discuss analysis strategies for these sessions including the proper use of datum or “transfer sources”.
KeywordsCelestial reference frames Earth orientation parameters ICRF VLBI
We gratefully acknowledge Chris Jacobs and two anonymous reviewers for their valuable and constructive comments which helped to improve the manuscript significantly. The authors acknowledge the International VLBI Service for Geodesy and Astrometry (IVS) and all its components for providing VLBI data (Nothnagel et al. 2015). The VLBA is operated by the National Radio Astronomy Observatory, which is a facility of the National Science Foundation, and operated under cooperative agreement by Associated Universities, Inc. Hana Krásná works within the Hertha Firnberg position T697-N29, funded by the Austrian Science Fund (FWF).
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