Dependence of large SEP events with different energies on the associated flares and CMEs

Abstract

To investigate the dependence of large gradual solar energetic particle (SEP) events on the associated flares and coronal mass ejections (CMEs), the correlation coefficients (CCs) between peak intensities of E > 10MeV (I10), E > 30MeV (I30) and E > 50MeV (I50) protons and soft X-ray (SXR) emission of associated flares and the speeds of associated CMEs in the three longitudinal areas W0-W39, W40-W70 (hereafter the well connected region) and W71-W90 have been calculated. Classical correlation analysis shows that CCs between SXR emission and peak intensities of SEP events always reach their largest value in the well connected region and then decline dramatically in the longitudinal area outside the well connected region, suggesting that they may contribute to the production of SEPs in large SEP events. Both classical and partial correlation analyses show that SXR fluence is a better parameter describing the relationship between flares and SEP events. For large SEP events with source location in the well connected region, the CCs between SXR fluence and I10, I30 and I50 are 0.58±0.12, 0.80±0.06 and 0.83±0.06 respectively, while the CCs between CME speed and I10, I30 and I50 are 0.56±0.12, 0.52±0.13 and 0.48±0.13 respectively. The partial correlation analyses show that in the well connected region, both CME shock and SXR fluence can significantly affect I10, but SXR peak flux makes no additional contribution. For E > 30MeV protons with source location in the well connected region, only SXR fluence can significantly affect I30, and the CME shock makes a small contribution to I30, but SXR peak flux makes no additional contribution. For E > 50 MeV protons with source location in the well connected region, only SXR fluence can significantly affect I50, but both CME shock and SXR peak flux make no additional contribution. We conclude that these findings provide statistical evidence that for SEP events with source locations in the well connected region, a CME shock is only an effective accelerator for E < 30MeV protons. However, flares are not only effective accelerators for E < 30MeV protons, but also for E > 30MeV protons, and E > 30MeV protons may be mainly accelerated by concurrent flares.