Oonk, J., van Weeren, R., Salgado, F., Morabito, L., Tielens, A., Rottgering, H., …Zensus, A. (2013). Discovery of carbon radio recombination lines in absorption towards Cygnus A. Monthly Notices of the Royal Astronomical Society, 437(4), https://doi.org/10.1093/mnras/stt2158