Solar Energetic Particle Events and Associated Type II Radio Bursts from Different Source Regions

TL;DR

This study statistically analyzes the relationship between solar energetic particle events, type II radio bursts, and source regions, revealing source-dependent properties and spectral correlations that inform SEP acceleration mechanisms.

Contribution

It provides new statistical insights into how source regions influence type II radio burst characteristics and their association with SEP events.

Findings

Nearly all SEP events are accompanied by type II radio bursts.

Type II burst duration and frequency characteristics depend on source region.

Proton spectra index correlates with the starting frequency of type II bursts.

Abstract

Large solar energetic particle (SEP) events are thought to originate from the shocks driven by fast coronal mass ejections (CMEs) and thus generally accompanied by type II radio bursts. However, a significant proportion of type II radio bursts is not accompanied by SEP events. To study the relationship between SEPs and type II radio bursts and the associated physical mechanisms, we statistically analyze 43 SEP halo-CMEs and 131 non-SEP halo-CMEs observed from 2010 to 2024, and check the related properties of type II radio bursts and solar source region. We find nearly all SEP events and approximately two-thirds of non-SEP events are accompanied by type II radio bursts. Type II radio bursts associated with SEP events usually have longer duration and lower ending frequencies. The starting frequency exhibits a clear source region dependence, being highest for ''single active region (AR)'', intermediate for ''multiple ARs'', and lowest for ''outside of ARs''. Furthermore, the spectra of both protons and electrons exhibit a similar softening trend in the three types of source regions. Joint analysis of spectra and type II radio bursts reveals that the proton spectra index has a good anti-correlation with the starting frequency of the type II radio bursts. Our statistical results have important implications for the mechanisms behind SEP acceleration