George C. Ho and Glenn M. Mason

1. Energetic Electrons in 3He Enhanced Solar Energetic Particle Events George C. Ho and Glenn M. Mason The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723 June 26th, 2008 Introduction Energetic Electrons Fluence Analysis Summary

2. Outline Helium-3 Helium-4 • Introduction • First Discovery • Classification Paradigm • Energetic Electron • Timing • Occurrence • Fluence Analysis • Observations • Implication • Discussion Relative Abundance 1 2500 Key: proton = neutron = electron = Introduction Energetic Electrons Fluence Analysis Summary

3. Introduction Introduction Energetic Electrons Fluence Analysis Summary

4. Discovery that small solar particle events sometimes showed enormous enrichments of 3He, without any accompanying 3H or 2H enrichments (Garrard, Stone & Vogt, NASA SP-342, 1973; Anglin et al. 1974; Serlemitsos & Balasubrahmanyan 1975) Anglin, 1975 Introduction Energetic Electrons Fluence Analysis Summary

5. Kilometric Type III Association Reames and Stone, 1986 Introduction Energetic Electrons Fluence Analysis Summary

6. Overall Picture as of Mid 1990s Introduction Energetic Electrons Fluence Analysis Summary

7. Gradual and Impulsive SEP Events Mason et al., 1989 Introduction Energetic Electrons Fluence Analysis Summary

8. ACE He Mass Resolution  keV/n  MeV/n Introduction Energetic Electrons Fluence Analysis Summary

9. Event onsets often show almost pure velocity dispersion -- but multiple events can overlap in time. These are separated in constructing fluence spectra

10. Solar Cycle Dependence ACE launched in August ‘97 Introduction Energetic Electrons Fluence Analysis Summary

11. 3He-rich Population Fraction of time with 3He present. Points are shown for individual Bartels rotations; lines show running average over 6 rotations. Unfilled circles and dotted line: unambiguous 3He (categories 2–4); filled circles and solid line: probable 3He (categories 1 and 5) also included. Wiedenbeck et al., Solar Wind 10 Introduction Energetic Electrons Fluence Analysis Summary

12. Ultra-Heavy Particles Mason et al. (2004) • Ultra-heavy ions ~200 times SW value • Acceleration depends on M/Q ratio • No satisfactory theory Mason et al., 2004 Introduction Energetic Electrons Fluence Analysis Summary

13. Coordinated Observations

14. Ionization States • Mean Q-states of Fe increase with Energy • At low-E - ionic charge states correspond to equilibrium Temperature • At high-E, stripping due to acceleration and transport Klecker et al. (2005) Introduction Energetic Electrons Fluence Analysis Summary

15. Energetic Electrons in 3He-rich Events Introduction Energetic Electrons Fluence Analysis Summary

16. Injection study of impulsive electrons ? e- beam SUN 107 106 105 104 Earth Freq (Hz) Flux UT Time 05:00 07:00 09:00 11:00 type III radio burst Linghua Wang et al. 2006 SPD

17. Casual Relationship Ho et al., 2001 Introduction Energetic Electrons Fluence Analysis Summary

18. Timing Analysis Ho et al., 2003 Introduction Energetic Electrons Fluence Analysis Summary

19. Scatter-free Transport Ho et al., 2003 Introduction Energetic Electrons Fluence Analysis Summary

20. Lack of Correlation Ho et al., 2001 Introduction Energetic Electrons Fluence Analysis Summary

21. Association with all Impulsive Events Ho et al., 2001 Introduction Energetic Electrons Fluence Analysis Summary

22. Fluence Analysis Introduction Energetic Electrons Fluence Analysis Summary

23. “Apparent” Anti-correlation Introduction Energetic Electrons Fluence Analysis Summary

24. Upper Limit on 3He Fluence • Measurements above instrument thresholds • 4He fluences range over a factor of 10,000 while the 3He fluences in the same SEP range over only a factor of 100 • 3He/4He does not order the data • A strict upper limit on the 3He fluence Introduction Energetic Electrons Fluence Analysis Summary

25. Fluence Distributions Ho, Roelof, Mason., 2005 Introduction Energetic Electrons Fluence Analysis Summary

26. 20Ne vs. 4He Fluences Ho, Roelof, Mason., 2005 Introduction Energetic Electrons Fluence Analysis Summary

27. Spectral Form-Class I • Class-1 Events: • power law or double power law form • above ~1 MeV/n all spectra similar • 3He is power law or double power law Mason et al., 2002 Introduction Energetic Electrons Fluence Analysis Summary

28. Spectral Form-Class I • Class-1 Events: • single power law for all species except 3He • 3He harder than others below ~1 MeV/n • 3He:4He peaks from 1-few MeV/n Mason et al., 2002 Introduction Energetic Electrons Fluence Analysis Summary

29. Spectral Form-Class II • Class-2 Events: • 4He is power law • 3He and Fe flatten notably at low energies (other heavy ion species not clear) • 3He and Fe curve at different energies • highest 3He: 4He Mason et al., 2002 Introduction Energetic Electrons Fluence Analysis Summary

30. Possible synthesis:  initial 3He enrichment mechanism (Cascade MHD?)  further acceleration results in power law spectra  still further acceleration results in similar spectra for all species

31. Fluence Distributions Ho, Roelof, Mason., 2005 Introduction Energetic Electrons Fluence Analysis Summary

32. Discussions • New observations from advanced instrumentations give us new insight into this class of SEP events • As we learned more about this class of events, we find there is more outstanding questions (personal views): • What enhancement/acceleration mechanism operate in this remarkable class of SEP event? (Ultra-heavy ion?) • Why is the 3He presented continuously in the interplanetary space? • What are the causal relationship between the energetic electrons, flare, and 3He enrichment? • Why is there an apparent upper limit on the 3He fluence in the interplanetary space? What is its implications? • Why the 3He spectral shape different from other ions? Introduction Energetic Electrons Fluence Analysis Summary

33. Discussions • Current observations at 1 AU are hampered by transport effects as we are far from the source • Require high resolution in-suite observation close to the source of the enrichment/acceleration Solar Orbiter: Solar Probe + : Introduction Energetic Electrons Fluence Analysis Summary

34. Fluence Analysis • The remarkable enrichment of the isotope 3He in solar energetic particle (SEP) events is usually described in terms of the ratio of the fluences of the two isotopes (3He/4He) • However, only weak correlations between 3He/4He and flare properties have been found [Reames, Dennis, and Stone, ApJ., 1988] • Strong correlation is found between the occurrence of 3He-rich SEP with energetic electrons [Reames, von Rosenvinge, and Lin, ApJ., 1985] • However, Ho et al. [ApJ., 2001] found same association in all impulsive SEP events with energetic electrons • Ho, Roelof, & Mason [ApJL., 2005] found during the peak of solar activity, there is an upper limited on the 3He flunence of 0.2 to 2.0 MeV/nuc. Introduction Energetic Electrons Fluence Analysis Summary