The MHz-peaked radio spectrum of the unusual γ-ray source PMN J1603–4904 C. Müller, P. R. Burd, R. Schulz, R. Coppejans, H. Falcke, H. Intema, M. Kadler, F. Krauß and R. Ojha A&A, 593 (2016) L19 Published online: 27 September 2016 DOI: 10.1051/0004-6361/201629547