Search for the Radio Sources with a Significant Change in the Coordinates

A. A. Osetrova, O. A. Titov, A. E. Melnikov

Transactions of IAA RAS, issue 64, 38–45 (2023)

DOI: 10.32876/ApplAstron.64.38-45

Keywords: AGN, quasars, apparent proper motion, reference frame, VLBI, unstable radio sources, IVS

Abstract

The third realization of the fundamental ICRS coordinate system is based on the positions of 4536 radio sources. The basis of the ICRF3 catalog consists of 303 «defining» objects, the floor accuracy of their positions reaches 30 mas. However, the recent VLBI observations (after the ICRF3 was released) have disclosed an unprecedented change in apparent positions of some ICRF3 radio sources (as much as 130 mas) over rather short time interval. This displacement significantly exceeds all previous known variations in radio source positions (within 3 mas). Using these objects as «reference» ones may lead to a significant loss of accuracy of other geodetic parameters (station positions, Earth Orientation Parameters, etc.). In the worst case, the whole geodetic VLBI experiment would be unusable for analysis. In the paper, we have analyzed the time series of radio source coordinates which based on the International VLBI Service (IVS) programme in 1993–2021 and 7 experiments obtained at the Institute of Applied Astronomy (IAA) the (Ru-A programme in 2019–2021). We found 64 radio sources with statistically significant change in positions, and distinguished three types of instability («bouncing» first and last points, «step» at the position time series, and steady apparent proper motion) using original statistical criteria. Such «unstable» radio sources should not be scheduled in standard geodetic VLBI experiments due to potentially severe loss of accuracy. In the context of next ICRF catalogue preparation, such radio sources should be moved in the list of astrometrically unstable objects.

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