The X/Ka-band (8.4/32 GHz) 2024a Celestial Reference Frame

Abstract: The X/Ka-band (8.4/32 GHz) Celestial Reference Frame became one of three components of the ICRF-3 in 2018. In the five years since, the X/Ka data set has increased by about 93% as well as adding the much needed north-south geometry from Japan to Australia. The latest solutions have 686 sources with median formal precisions of 43 μas in α cosδ and 62 μas in δ.

The large spherical harmonic distortions seen in the ICRF3-X/Ka are greatly improved with the Z-dipole term reduced from 314 μas to a statistically insignificant -49 +- 40 μas and with the quadrupole 2,0 magnetic term of 186 +- 15 μas and a quadrupole 2,0 electric term of 80 +- 24 μas. We note that the X/Ka frame is derived from a limited geometry of only five observing sites of which the two DSN baselines dominate with 85% of the total data thus creating a susceptibility of this frame to geometric distortions. The prospects for future improvements are bright and we expect the distortions to be reduced as more data from the ESA Malargüe and JAXA Misasa stations are added.