Electron acceleration at Collisionless Shocks

The electron injection problem pertains to the long-standing problem of explaining the origin of ultra-relativistic cosmic ray electrons observed throughout the universe. It is commonly accepted that cosmic ray particles (ions and electrons) are accelerated to immense ultra-relativistic energies at supernova remnant shock waves. However, the theory through which these particles are accelerated, the Diffusive Shock Acceleration (DSA) theory, only works if the particles already have a sufficient high enough starting energy to enter the process. For electrons, this typically means they have to already be relativistic to be injected into the DSA process. Hence, there must be other process to explain electron acceleration up to relativistic energies (~500 keV). This work uses spacecraft missions to study suprathermal electron acceleration at collisionless shock waves found in the heliosphere. Focusing on a case study at Earth’s bow shock and a comparison of the electron acceleration efficiency between the Venusian and terrestrial bow shocks.