Rapid energization of electrons to relativistic and ultra-relativistic energies by interplanetary (IP) shocks

Interplanetary (IP) shocks are known to energize electrons very rapidly on the order of a few minutes, when they impact the magnetosphere. The shock compresses the magnetosphere and result in a bipolar electric field pulse and electrons "surf" that pulse resulting in energization and inward radial motion. The resulting electrons are usually injected as a bunch and drift around producing drift echoes. It is reasonable to expect that the properties of injected electrons, such as spectral hardness be related to the IP shock properties, such as shock strength. However, there are very few systematic correlative studies done to date to connect shock properties to those of the energized electrons.

Our study seeks to understand the relationship between IP shock characteristics and the energized electron injections produced by the shock. In order to understand possible underlying physical processes in detail, we correlate the IP shock properties to the injected electron spectral variability. The energetic electron data are obtained by the Relativistic Electron Proton Telescope (REPT) onboard the Van Allen Probes mission. We study the injections initiated by IP shocks occurring during the declining phase of current solar cycle, i.e., during the period from 2015 to July 2019. The IP shock properties are obtained from public databases from Wind, ACE and Soho spacecraft. Our preliminary survey shows that there are over 60 IP shocks during this period (www.cfa.harvard.edu/shocks/).