Imaging ICRF3 sources at 0.2 mas resolution with the European VLBI Network at K band

The presentation reports on the results of imaging extragalactic radio sources at K band (22 GHz) from observations conducted with the European VLBI Network (EVN). These data were acquired as part of the JUMPING JIVE project with the primary goal of measuring the geodetic positions of non-geodetic EVN antennas (i.e. antennas not equipped with the proper dual-frequency S/X (2.3/8.4 GHz) receivers traditionally used for geodesy). To this end, two experiments have been carried out, in June 2018 and October 2020. The EVN includes long East-West and North-South baselines (from Europe to Asia and from Europe to South Africa) along with baselines of shorter and intermediate lengths within Europe, making it a prime network for imaging. In all, 17 EVN telescopes have the capability to observe at K band, allowing for a resolution of 0.2 mas. The vast majority of these telescopes participated in the said experiments. The network for the October 2020 experiment was further augmented with the four e-MERLIN out-stations (in the UK) and the 26~m antenna in Hobart (Australia), thus forming a large array of 22 stations. Scheduling was accomplished by using sub-netting to optimize the sky coverage at each telescope, as in standard geodesy experiments. In this scheme, a minimum of four stations per sub-net was also ensured to provide useful closure quantities for imaging. A total of 80 different sources belonging to the third realization of the International Celestial Reference Frame (ICRF3) were observed in the October 2020 experiment, all of which are defining sources. The imaging results from that experiment, which are solely reported in the presentation, demonstrates the capability of the EVN to image large number of sources, with about 30% increased resolution compared to the Very Long Baseline Array. As expected, the majority of the sources were found to be quite compact. Southern stations (Hartrao, Hobart) are essential to image low-declination sources. Future plans include continuing observations with the EVN for mixed geodetic, astrometric and imaging goals. The VLBI images will be made publicly available through the Bordeaux VLBI Image Database, which may be accessed at https://bvid.astrophy.u-bordeaux.fr/.