New calibration sources for very long baseline interferometry at 1.6 GHz

Abstract

I present new 1.6 GHz VLBI observations of sample of 43 radio sources in the Southern celestial Hemisphere. My goals were firstly to establish the suitability of the 43 sources as calibrators for 1.6 GHz VLBI observations, and secondly to determine, based on some selected sources from the sample, how the properties of the sources seen at 8.4 GHz are related to those seen at 1.6 GHz. I used seven telescopes; ASKAP, ATCA, Ceduna, Hobart, Mopra and Parkes from Australia, and HartRAO from South Africa. By evaluating the sources radial extents, flux density of the central components of the sources and their brightness, I classified the sources into very good, good, intermediate and bad calibrators. Among the 43 sources, I found that 38 sources fell into the good or very good calibrator classes. Among 35 of our sources, which are known to be good calibrators at 8.4 GHz, I found that 32 sources fell into the good or very good calibrator classes. Of the basis of my sample therefore, I can say that 91 percent of the good calibrators at 8.4 GHz are also safe to use at 1.6 GHz.