Solar Source Regions for³He‐rich Solar Energetic Particle Events Identified Using Imaging Radio, Optical, and Energetic Particle Observations

Abstract

We have identified the sources of six impulsive 3 He-rich solar energetic particle events using imaging radio, optical, and energetic ion and electron data, together with calculated coronal fields obtained from extrapolating photospheric magnetograms using a potential field source surface ( PFSS) model. These events were all studied in 2006 by Wang et al., who identified the particle sources as typically small, flaring active regions lying next to a coronal hole containing Earth-directed open field lines, located between W33 and W65 . By introducing radio imaging data we were able in one case to conclusively identify which of two simultaneous EUV jets was associated with the particle source. In addition, type III radio burst and energetic electron data introduced in this study constrain the injection times much more accurately than possible with low-energy ion data used in Wang et al. These new observations confirm the source identifications of Wang et al. and remove many of the remaining uncertainties. All of these events were associated with narrow, fast coronal mass ejections (CMEs), which are unusual for 3 He-rich solar energetic particle (SEP) events. Although the CMEs generally were ejected in directions well off the ecliptic plane, the PFSS calculations show the presence of magnetic field lines that made it possible for the energetic particle to quickly reach Earth. Some of these impulsive events were observed during periods in which 3 He was observed continuously over several days.

A tiny event producing an interplanetary type III burst

“…Type III radio bursts are known to be associated not only with flares, but also with Hα ejecta (Axisa et al 1973), X-ray bright points (Kundu et al 1994(Kundu et al , 1995a, soft X-ray transient brightenings (Nindos et al 1999), and soft X-ray or/and extreme-UV (EUV) jets (Kundu et al 1995b;Raulin et al 1996;Pick et al 2006;Nitta et al 2008;Innes et al 2011;Krucker et al 2011;Klassen et al 2011Klassen et al , 2012Chen et al 2013a,b). Jets that are correlated with type III bursts accompany flaring activity that ranges from weak transient brightenings and subflares (Kundu et al 1995b;Raulin et al 1996;Nitta et al 2008) to M-class flares (Krucker et al 2011;Chen et al 2013a).…”

“…Their dimensions may range from about 10 4 km to more than about 10 5 km. They appear most frequently at the edge of active regions and sometimes (Pick et al 2006) close to the border of an active region and a coronal hole.…”

Coronal magnetic topology and the production of solar impulsive energetic electrons

“…The impulsive SEP event that occurred on 2002 October 20 gives us an excellent opportunity to carry out this cross disciplinary study. This event had been partially discussed by several other authors (Wang et al 2006b;Pick et al 2006;Wang et al 2011). Unlike previous studies, we derive the solar particle release (SPR) times of SIEEs by considering the instrumental effect and find double injections of electrons at the Sun.…”

“…Fe). Traditionally, it was believed that solar flares rather than coronal mass ejections (CMEs) are the acceleration sources of impulsive SEPs, even though some unusual cases appear to be associated with narrow or jet-like CMEs (Wang et al 2006a;Pick et al 2006). Recently, Wang et al (2012) carried out a statistical survey of electron events over one solar cycle and found that only ∼35% of them are related to a reported flare, as compared to that of ∼60% that are related to a CME and to that of ∼50% for which these CMEs are narrow.…”

“…Therefore, coronal magnetic topology indeed plays an important role in triggering solar eruptions and guiding energetic particles. Several authors (Wang et al 2006b;Pick et al 2006;Rust et al 2008;Mason et al 2009;Li et al 2010Li et al , 2011 have presented magnetic flux tubes rooted in solar active regions (ARs) that made it possible for energetic particles to easily escape from acceleration sites and quickly reach the Earth .…”