Unexpected cyclic behavior in cosmic ray protons observed by PAMELA at 1 AU

TL;DR

This study analyzes cosmic ray protons detected by PAMELA from 2006 to 2014, revealing an unexpected 450-day quasi-periodicity below 15 GV, possibly linked to Jupiter's magnetosphere, suggesting a new contribution to cosmic ray modulation.

Contribution

It uncovers a novel 450-day periodicity in cosmic ray protons and explores a potential Jovian origin, expanding understanding of cosmic ray sources and solar modulation effects.

Findings

Detected a 450-day quasi-periodicity in proton flux below 15 GV.

Evidence suggests a possible contribution from Jupiter's magnetosphere.

The periodicity indicates a new factor influencing cosmic ray modulation.

Abstract

Protons detected by the PAMELA experiment in the period 2006-2014 have been analyzed in the energy range between 0.40-50 GV to explore possible periodicities besides the well known solar undecennial modulation. An unexpected clear and regular feature has been found at rigidities below 15 GV, with a quasi-periodicity of $\sim$450 days. A possible Jovian origin of this periodicity has been investigated in different ways. The results seem to favor a small but not negligible contribution to cosmic rays from the Jovian magnetosphere, even if other explanations cannot be excluded.