Electron pulsations generated by rotating magnetospheric dynamics at Saturn

Quasi-periodic pulsations of energetic electrons have been frequently observed in Saturn's magnetosphere. The mechanisms for the electron pulsations are far from conclusive, although generally believed to be associated with field-line resonance due to their similar periodicities. Here we report an electron pulsation event that is related to aurora beads and energetic neutral atom (ENA) emissions. The perturbation of the magnetic field indicates that Cassini spacecraft encountered a series of field-aligned currents (FACs) connected to the aurora beads. The fluxes of energetic electrons were enhanced when the spacecraft crossed the FACs. Both aurora beads and ENA emission were rotating. Given that the FACs interconnect the aurora beads and the active region at equator, a hot plasma population associated with the ENA enhancement, we conclude that the FACs were rotating with Saturn and had finite extent in the azimuthal direction. The periodic features also manifested in the whistler-mode auroral hiss emissions in the same event. We proposed that the electron pulsations we studied are spatial effect of the rotating magnetosphere. The rotation of the whole magnetosphere transfers the spatial effect to the temporal effect, i.e., the pulsation sequences observed by Cassinis multiple instruments.