Observations & positions of 377 AGNs using VLBI

Their positions form a celestial reference frame that plays an important role in both astronomy and geodesy. This study investigates the accuracy and stability of the positions of the AGNs that are measured by simultaneous VLBI observations at 3.3, 5.5, 6.6, and 10.5GHz.

Based on position time series from dedicated geodetic solutions, we characterize the observed source position variations and identify the possible factors causing such variations. We find that the primary contributor is source structure for sources above 20{deg} decl., while the sensitivity of the observations to the decl. coordinate predominates for sources below 20{deg} decl. The position time series are further explored to derive more realistic uncertainties for the quad-band positions.