Relativistic protons' (>20 MeV) observation deep into the inner magnetosphere

Solar wind particles and the interaction of the Earth's magnetic field with the interplanetary drivers greatly affect the evolution of the inner magnetospheric particle. However, the relativistic protons are those uniquely trapped particles in the Earth's magnetosphere that has extremely high energies but much more stable than electrons. For each geomagnetic storm with Sym-H<;-50 nT, we investigated that there is no observable proton flux, measured by REPT instrument on board Van Allen probes, beyond L=3 [1]. However, after the launch of Van Allen probes era in 2012, the first strongest solar flare of solar cycle 24 erupted with X9.3 class that accompanied the most energetic proton event, since past one decade. During this event, Van Allen probes made a very important and crucial observations of these most energetic radiation belt protons, deep into the inner magnetosphere. During 10-12 Sep 2017, Van Allen probes recorded the highest proton flux since its launch. It increased by several order that persisted for ~2 days. In this paper we importantly focused on this rare event by studying the extent of proton flux enhancement and its penetration deep into the inner magnetosphere. Moreover, we analyzed the related mechanism for the proton flux injection and loss during September 2017.