The Celestial Reference Frame at K Band: Imaging. I. The First 28 Epochs
Aletha de Witt, C. S. Jacobs, David Gordon, M. F. Bietenholz, Marisa Nickola, Alessandra Bertarini
Abstract
Abstract We present K -band (24 GHz) images of 731 compact extragalactic radio sources with submilliarcsecond resolution, based on radio interferometric observations made with the Very Long Baseline Array of 10 telescopes during 29 day long sessions spanning from 2015 to 2018 and recorded at 2048 Mbps. Many of these sources are imaged with submilliarcsecond resolution for the first time at frequencies above X band (8 GHz). From each of the K -band images, we derive the following source properties: peak brightness, core and total flux density, the ratio of peak and core to total flux (compactness measure), radial source extent, structure index, source size, and jet direction. The vast majority of sources are imaged at multiple epochs, providing insights into their temporal behavior. The use of K band was motivated by the fact that the sources are generally intrinsically more compact at higher frequencies, as well as by the factor of 3 improvement in interferometer resolution relative to the historically standard S / X band (2.3/8.4 GHz) used for a large amount of reference frame and calibrator work. Lastly, as most of the sources imaged here are in the K -band component of the third International Celestial Reference Frame, these images serve to characterize the objects used in that International Astronomical Union standard.