Imaging, Modelfitting, and Source Structure Corrections for the K-band (24 GHz) Celestial Reference Frame

Abstract

The K-band (24-GHz) celestial reference frame (K-CRF) program, supported through the United States Naval Observatory’s (USNO) 50% timeshare allocation of the Very Long Baseline Array (VLBA), has so far provided high-resolution VLBA images for more than 800 Active Galactic Nuclei (AGN) at up to 81 epochs, as part of extending the International Celestial Reference Frame (ICRF) to K-band. A comprehensive analysis of these images has yielded metrics that serve as indicators for the suitability of each source as a calibrator or reference point. Additionally, our modelling efforts provide crucial insights into the overall dimensions and orientation of the source structure. Although AGN such as the Celestial Reference Frame (CRF) sources typically appear more compact at K-band than at X-band (8.4 GHz), they can, on occasion, still display noticeable extended emissions at K-band. We therefore initiated a project aimed at modelling structure effects in the astrometric analysis process. This involves utilizing readily available K-CRF VLBI images and up-to-date source structure models. This paper offers an overview of our image analysis efforts and outlines our plans to investigate the impact of source structure using all available K-CRF sources.