MULTI-SPACECRAFT OBSERVATIONS OF RECURRENT³He-RICH SOLAR ENERGETIC PARTICLES

Abstract

We study the origin of 3 He-rich solar energetic particles (<1 MeV nucleon −1 ) that are observed consecutively on STEREO-B, ACE, and STEREO-A spacecraft when they are separated in heliolongitude by more than 90 • . The 3 He-rich period on STEREO-B and STEREO-A commences on 2011 July 1 and 2011 July 16, respectively. The ACE 3 He-rich period consists of two sub-events starting on 2011 July 7 and 2011 July 9. We associate the STEREO-B July 1 and ACE July 7 3 He-rich events with the same sizeable active region producing X-ray flares accompanied by prompt electron events, when it was near the west solar limb as seen from the respective spacecraft. The ACE July 9 and STEREO-A July 16 events were dispersionless with enormous 3 He enrichment, lacking solar energetic electrons and occurring in corotating interaction regions. We associate these events with a small, recently emerged active region near the border of a low-latitude coronal hole that produced numerous jet-like emissions temporally correlated with type III radio bursts. For the first time we present observations of 1) solar regions with long-lasting conditions for 3 He acceleration and 2) solar energetic 3 He that is temporary confined/re-accelerated in interplanetary space. Subject headings: interplanetary medium -solar wind -Sun: flares -Sun: particle emission a event included in survey by Bučík et al. (2013a) b event included in survey by Bučík et al. (2013b) c at event start time d 320-450 keV nucleon −1 ; fluence units -particles (cm 2 sr MeV/nucleon) −1

3He-rich Solar Energetic Particles in Helical Jets on the Sun

“…The approximate event periods were identified using the 250-900 keV nucleon −1 He measurements in the mass spectrograms in Figure 2c. The fractions of ions that spill into the 3 He or 4 He peaks were estimated on the basis of the SIT observations of a clean 4 He peak (see Figure 3) and the cleanest 3 He peak (Bučík et al 2013). The background with a signature at ∼1 MeV nucleon −1 is due to cosmic rays penetrating the SIT telescope housing.…”

“…Figure 4d shows Fe/O versus 3 He/ 4 He obtained from all (109) previously reported 3 He-rich SEP events at suprathermal ( 1 MeV nucleon −1 ) energies. Specifically, the 3 He/ 4 He ratio is reported at 320-450 keV nucleon −1 in 67 events (Mason et al 2002(Mason et al , 2004Wang et al 2006;Bučík et al 2013Bučík et al , 2014Bučík et al , 2016, at 400-600 keV nucleon −1 in 11 events Pick et al 2006), and at 0.5-2 MeV nucleon −1 in 31 events (Tylka et al 2002;Nitta et al 2015;Mason et al 2016 Table 1 was a factor of ∼3-5 lower than the Fe fluences in the first five spectral points (97-386 keV nucleon −1 ) of event 2 and comparable to the fluences in event 1. The Fe/O ratio of 1.4 in 2001 April 14 event was similar to values in our events, but the 3 He/ 4 He ratio attained only ∼6.5% (c.f.…”

“…Flares associated with 3 He-rich SEP events are commonly observed as collimated or jet-like form in extremeultraviolet (EUV) or X-ray images (Nitta et al 2006(Nitta et al , 2008(Nitta et al , 2015Bučík et al 2014Bučík et al , 2015Bučík et al , 2016Chen et al 2015). Sometimes jets show a high-altitude extension in white-light coronograph observations (Kahler et al 2001;Wang et al 2006).…”

“…Reconnecting magnetic field impulsively releases energy which is available for particle acceleration (Benz & Güdel 2010). The underlying photospheric source of 3 He-rich SEPs is typically a small, compact active region often found next to a coronal-hole Bučík et al 2014). …”

“…The only example of an Xray jet associated with 3 He-rich SEPs is probably also a blowout type (Nitta et al 2008). One recurrent jet in a study of Bučík et al (2014) appears to be a standard jet, but another is probably blowout type. The jets in two 3 He-rich SEP events, that trigger EUV wave, were blowout type (one with a helical motion) as could be inferred from the animations in Bučík et al (2015).…”