High-energy particle enhancements in the solar wind upstream Mercury during the first BepiColombo flyby: SERENA/PICAM and MPO-MAG observations

Abstract

Context. The first BepiColombo Mercury flyby offered the unique opportunity to simultaneously characterize the plasma and the magnetic field properties of the solar wind in the vicinity of the innermost planet of the Solar System (0.4 AU). Aims. In this study, we use plasma observations by SERENA/PICAM and magnetic field measurements by MPO-MAG to characterize the source with intermittent features (with a timescale of a few minutes) at ion energies above 1 keV observed in the solar wind upstream of Mercury. Methods. The solar wind properties have been investigated by means of low-resolution magnetic field (1 s) and plasma (64 s) data. The minimum variance analysis and the Lundquist force-free model have been used. Results. The combined analyses demonstrate that the intermittent ion features observed by PICAM at energies above 1 keV can be associated with the passage of an interplanetary magnetic flux rope. We also validate our findings by means of Solar Orbiter observations at a larger distance (0.6 AU). Conclusions. The core of an interplanetary magnetic flux rope, hitting BepiColombo during its first Mercury flyby, produced high-energy (> -pagination1 keV) intermittent-like particle acceleration clearly distinct from the background solar wind, while at the edges of this interplanetary structure compressional low-energy fluctuations have also been observed.