In Situ Measurement of the Energy Fraction in Suprathermal and Energetic Particles at ACE, Wind, and PSP Interplanetary Shocks

Liam David, Federico Fraschetti, Joe Giacalone, Robert F. Wimmer-Schweingruber, Lars Berger, David Lario

Research output: Contribution to journalArticlepeer-review

Abstract

The acceleration of charged particles by interplanetary shocks (IPs) can drain a nonnegligible fraction of the plasma pressure. In this study, we have selected 17 IPs observed in situ at 1 au by the Advanced Composition Explorer and the Wind spacecraft, and 1 shock at 0.8 au observed by Parker Solar Probe. We have calculated the time-dependent partial pressure of suprathermal and energetic particles (smaller and greater than 50 keV for protons and 30 keV for electrons, respectively) in both the upstream and downstream regions. The particle fluxes were averaged for 1 hr before and 1 hr after the shock time to remove short timescale effects. Using the MHD Rankine-Hugoniot jump conditions, we find that the fraction of the total upstream energy flux transferred to suprathermal and energetic downstream particles is typically ≤ 16%, in agreement with previous observations and simulations. Notably, by accounting for errors on all measured shock parameters, we have found that for any given fast magnetosonic Mach number, M f < 7, the angle between the shock normal and average upstream magnetic field, θ Bn, is not correlated with the energetic particle pressure; in particular, the partial pressure of energized particles does not decrease for θ Bn ≥ 45°. The downstream electron-to-proton energy ratio in the range ≥ 140 eV for electrons and ≥ 70 keV for protons exceeds the expected ∼1% and nears equipartition (>0.1) for the Wind events.

Original languageEnglish (US)
Article number66
JournalAstrophysical Journal
Volume928
Issue number1
DOIs
StatePublished - Mar 1 2022

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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