Multi-Frequency Imaging Results of 453 Extragalactic ICRF-3 Radio Sources from Multi Epoch, Near-Simultaneous Astrometric VLBA Observations

We present multi-frequency images of 452 compact extragalactic radio sources | most of them from the ICRF-3|with sub-milliarcsecond (sub-mas) resolution, based on Very Long Baseline Array (VLBA) imaging observations taken between April and June 2021. We compare images and astrometry from S (2.3 GHz), X (8.4 GHz), K (24 GHz) and Q-band (43 GHz) in order to study the astrophysical di erences and determine the optimal frequency band for Celestial Reference Frame observations. In order to do this we conducted multi-epoch, quasi-simultaneous S/X, K and Q- band astrometric-imaging observations. We characterise each source by the following properties: peak brightness, core and total ux density, the ratio of peak and core to total ux (compactness measure), radial source extent, structure index, source size, and jet direction. We will show how source structure compares amongst all four bands and we will assess the potential advantages of higher radio frequencies for Celestial Reference Frame work.