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Christopher Jacobs
Type of contribution: poster

The X/Ka-band (8.4/32 GHz) Celestial Frame: Can it be more accurate than the ICRF2?

Christopher S. Jacobs, JPL Cristina García-Miró, INTA/NASA  S. Horiuchi, CSIRO/NASA Lawrence G. Snedeker, SaiTech/NASA J.Eric Clark, JPL Robserto Maddè, ESA  Matia Mercolino, ESA  Charles J. Naudet, JPL Diego Pazos, Telespazio Phil Pope, CSIRO/NASA  Ioana Sotuela, ITNA/NASA Leslie A. White, JPL

Observations at X/Ka-band are motivated by their ability to access more compact source morphology and reduced core shift relative to observations at the historically standard S/X-band. In addition, the factor of four increase in interferometer resolution at Ka-band should resolve out some wide binary black holes which are a topic of concern for AGN centroid stability. Given these motivations, an X/Ka-band (8.4/32 GHz) celestial reference frame has been constructed using a combined NASA and ESA Deep Space Network.  In 110 observing sessions we detected 660 sources covering the full 24 hours of right ascension and the full range of declinations. The resulting XKa median precision is now comparable to the ICRF-2 precision thereby raising the question of which frame is more accurate. Comparison of about 530 X/Ka sources in common with the S/X-band (2.3/8.4 GHz) ICRF2 produced wRMS agreement of about 200 uas. There is evidence for systematic errors at the 100 uas level. Known errors include limited SNR, lack of phase calibration, troposphere mismodelling, and terrestrial frame distortions. Actions are underway to reduce all of these errors. In particular, a collaboration between NASA and the ESA deep space antenna in Malargüe, Argentina is quickly reducing weaknesses in the southern hemisphere. By looking at the best observed sources, we probe the accuracy limits of current celestial frames in an effort to understand the advantages of each frame.