Frequency analysis of the rf emission of oscillating Josephson supercurrent is a powerful passive way of probing properties of topological Josephson junctions. In particular, measurements of the Josephson emission enables to detect the expected presence of topological gapless Andreev bound states that give rise to emission at half the Josephson frequency f_J, rather than conventional emission at f_J. Here we report direct measurement of rf emission spectra on Josephson junctions made of

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... ed gate-tunable topological weak links. The emission spectra exhibit a clear signal at half the Josephson frequency f_ J/2. The linewidths of emission lines indicate a coherence time of 0.3-4ns for the f_ J/2 line, much shorter than for the f_ J line (3-4ns). These observations strongly point towards the presence of topological gapless Andreev bound states, and pave the way for a future HgTe-based platform for topological quantum computation.