Characteristics of events with metric-to-decahectometric type II radio bursts associated with CMEs and flares in relation to SEP events

A gradual solar energetic particle (SEP) event is thought to happen when particles are accelerated at a shock due to a fast coronal mass ejection (CME). To quantify what kind of solar eruptions can result in such SEP events, we have conducted detailed investigations on the characteristics of CMEs, solar flares and metric-to-decahectometric wavelength type II radio bursts (herein after m-to-DH type II bursts) for SEP-associated and non-SEP-associated events, observed during the period of 1997–2012. Interestingly, 65% of m-to-DH type II bursts associated with CMEs and flares produced SEP events. The SEP-associated CMEs have higher sky-plane mean speed, projection corrected speed, and sky-plane peak speed than those of non-SEP-associated CMEs respectively by 30%, 39%, and 25%, even though the two sets of CMEs achieved their sky-plane peak speeds at nearly similar heights within LASCO field of view. We found Pearson’s correlation coefficients between the speeds of CMEs (sky-plane speed and corrected speed) and logarithmic peak intensity of SEP events are cc=0.62$\mathit{cc} = 0.62$ and cc=0.58$\mathit{cc} = 0.58$, respectively. We also found that the SEP-associated CMEs are on average of three times more decelerated (−21.52ms−2$-21.52~\mbox{m}\, \mbox{s}^{- 2}$) than the non-SEP-associated CMEs (−5.63ms−2$- 5.63~\mbox{m}\, \mbox{s}^{-2}$). The SEP-associated flares have a mean peak flux (1.85×10−4Wm−2$1.85 \times 10^{- 4}~\mbox{W}\, \mbox{m}^{- 2}$) three times larger than that of non-SEP-associated flares, even though the flare duration (rise time) of both sets of events is similar. The SEP-associated m type II bursts have higher frequency drift rate and associated shock speed than those of the non-SEP-associated events by 70% and 25% respectively. The average formation heights of m and DH type II radio bursts for SEP-associated events (1.31Ro$1.31~R_{\mathrm{o}}$ and 3.54Ro$3.54~R_{\mathrm{o}}$, respectively) are lower than for non-SEP-associated events (1.61Ro$1.61~R_{\mathrm{o}}$ and 3.91Ro$3.91~R_{\mathrm{o}}$, respectively). 93% of SEP-associated events originate from the western hemisphere and 65% of SEP-associated events are associated with interacting CMEs. The obtained results indicate that, at least for the set of CMEs associated with m-to-DH type II bursts, SEP-associated CMEs are more energetic than those not associated with SEPs, thus suggesting that they are effective particle accelerators.