Evidence that Interaction with the Spacecraft Plasma Wake Generates Plasma Waves Close to the Electron Cyclotron Frequency in the Near-Sun Solar Wind

Prior observations of the near-Sun solar wind (sunward of 0.25 au) identified frequent, intense plasma waves near the local electron cyclotron frequency (fce), and its harmonics. In this Letter, it is shown that near-fce wave properties are consistent with generation via interaction between the observing spacecraft's ion wake and the ambient plasma and magnetic fields. This result implies that many observed near-fce waves are not intrinsic to the unobstructed solar wind flow, and therefore are unlikely to play a significant role in the dynamic evolution of particle distributions in the solar wind.