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The cometary plasma environment at low gas production rates is dominated by highly compressional, large-amplitude magnetic field waves in the 10-100 mHz range. They are thought to be caused by an ion-Weibel instability due to a cross-field current, which is caused by the cometary ions that are accelerated along the solar wind convective electric field. We devise a new method to determine the location of the wave source, the wave power, frequency, and bandwidth. It is found that the wave occurs everywhere in the coma, regardless of electric field direction. There is no correlation between the wave frequency and the measured plasma density. This is not in agreement with previous studies. A dependence of the frequency on the position of the spacecraft in a comet-fixed frame is in agreement with the prediction from the ion-Weibel instability. We infer a wave generation region much larger than the cometocentric distances covered by Rosetta.

Plain Language Summary We study the properties and region of occurrence of so-called singing comet waves. This type of electromagnetic wave has only been observed at comet 67P/Churyumov-Gerasimenko at low gas production rates. Contrary to previous simulations our results indicate that this wave is not only found in one hemisphere of the comet's plasma environment. Instead it is generated in a much bigger region around the nucleus than previously considered.