Relationships Between the Spectra of Near-Earth Proton Enhancements, Hard X-Ray Bursts, and CME Speeds

Abstract

Some studies propose the transfer of flare-accelerated protons in an erupting flux rope until its reconnection with an open structure releases the trapped protons. Coulomb collisions in the dense flux-rope body deplete the low-energy part of the proton spectrum. On the other hand, shock acceleration progressively replenishes this part of the spectrum. These processes form a double power-law proton spectrum that is usually observed at the Earth's orbit. We analyze the correlations between the slopes of near-Earth proton spectra below and above the break energy, on the one hand, and photon indices of the corresponding hard X-ray (HXR) bursts and speeds of associated coronal mass ejections (CMEs), on the other hand. We use catalogs of proton events in 1991 - 2006, HXR spectra obtained by Yohkoh and the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI), and CME catalogs. Significant correlations have been found between the proton spectral slopes i) above the break energy and HXR spectral indices (0.86), and ii) below the break energy and CME speeds (−0.75). The results indicate a statistical predominance of flare acceleration at higher proton energies and shock acceleration at their lower energies. The highest-energy proton spectra reconstructed in ground-level events exhibit the second break with the steepest slope above it. Neither this slope nor the second-break energy correlates with any other parameter. This peculiarity requires understanding.