An Introduction of the 3rd Realization of the International Celestial Reference Frame (ICRF3)

Abstract

The 3rd realization of the International Celestial Reference Frame, ICRF3, has been the latest ICRF (the International Celestial Reference Frame) as the replacement of its previous realization, ICRF2, since January 1, 2019. The ICRF3 is aligned to the ICRS (the International Celestial Reference System) to within the accuracy of the ICRF2. After its publication, the ICRF3 has played a vital role in many scientific disciplines.

The ICRF3 has some largely improved characteristics compared to the ICRF1 and the ICRF2: (1) In addition to the traditional S/X band (8.4 / 2.3 GHz) reference frame, the ICRF3 also contains two higher frequency band frames, namely K band (24 GHz) and X/Ka band (8.4 / 32 GHz). (2) The ICRF3 is the first reference frame that considers the influence of the Galactic aberration effect, and reports the source position at the epoch of 2015.0.

Having an overall understanding of the ICRF3, especially its new features, is very important for using it correctly. In this paper, we introduce the basic information of the ICRF3 in detail, and offer guidelines for users. We also provide comparisons between the different band frames of the ICRF3, and between the ICRF3 and the Gaia-CRF3. Through the comparisons of different catalogues, we test the stability of the ICRF3, and discuss the systematic errors in it.