Relativistic Electron Phase Space Density Distribution in Jovian Plasma Sheet Observed by Juno

Jupiter's inner radiation belts contain ultra-relativistic electrons capable of emitting intense synchrotron radiation. Earlier modeling suggested that these electrons were accelerated through radial diffusion from the outer magnetosphere. We performed a survey of electron phase space density in Jovian plasma sheet using the relativistic electron measurements by Juno during the first 24 orbits. We selected the periods when Juno travelled close to the magnetic equator, with local minima of the magnetic fields and enhancement of electron fluxes in the plasma sheet. The equatorially mirroring electron fluxes significantly increase with decreasing M shell, and the electron phase space densities increase from the outer magnetosphere to M shell of 20-30 at various first adiabatic invariants. The radial profile of phase space density indicates an internal acceleration source over 20 - 30 R_J, similar to the internal peaks in electron phase space density discovered in the Earth's outer radiation belts. Our results suggest an operative internal acceleration process contributing to the high relativistic electron flux in Jovian radiation belts.