PAMELA's Measurements of Magnetospheric Effects on High Energy Solar Particles

Abstract

The nature of particle acceleration at the Sun, whether through flare reconnection processes or through shocks driven by coronal mass ejections (CMEs), is still under scrutiny despite decades of research. The measured properties of solar energetic particles (SEPs) have long been modeled in different particle-acceleration scenarios. The challenge has been to disentangle to the effects of transport from those of acceleration. The Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) instrument, enables unique observations of SEPs including composition and the angular distribution of the particles about the magnetic field, i.e. pitch angle distribution, over a broad energy range (>80 MeV) -- bridging a critical gap between space-based measurements and ground-based. We present high-energy SEP data from PAMELA acquired during the 2012 May 17 SEP event. These data exhibit differential anisotropies and thus transport features over the instrument rigidity range. SEP protons exhibit two distinct pitch angle distributions; a low-energy population that extends to 90° and a population that is beamed at high energies (>1 GeV), consistent with neutron monitor measurements. To explain a low-energy SEP population that exhibits significant scattering or redistribution accompanied by a high-energy population that reaches the Earth relatively unaffected by dispersive transport effects, we postulate that the scattering or redistribution takes place locally. We believe these are the first comprehensive measurements of the effects of solar energetic particle transport in the Earth's magnetosheath.

21 pages, 4 figures. Accepted for publication in The Astrophysical Journal Letters

References in corpus (4)

• Observation of an anomalous positron abundance in the cosmic radiation
• A new measurement of the antiproton-to-proton flux ratio up to 100 GeV in the cosmic radiation
• PAMELA - A Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics
• The cosmic-ray electron flux measured by the PAMELA experiment between 1 and 625 GeV

Cited by in corpus (4)

• Spectral Analysis of the September 2017 Solar Energetic Particle Events
• Calibration of the GOES-13/15 high energy proton detectors based on the PAMELA solar energetic particle observations
• 3D propagation of relativistic solar protons through interplanetary space
• Geomagnetically trapped, albedo and solar energetic particles: trajectory analysis and flux reconstruction with PAMELA