Particle Acceleration in Solar Energetic Particle (SEP) Events and Solar Flares

1. Particle Acceleration in Solar Energetic Particle (SEP) Events and Solar Flares R. P. Lin Physics Department & Space Sciences Laboratory University of California, Berkeley, CA, USA For fall 2009 semester: School of Space Research, Kyung Hee University, Yongin, Gyeonggi 446-701, South Korea, Thanks to the RHESSI team & the Wind 3DP team

2. Forbush, S., Phys. Rev. Lett., 70, 771, 1946“…unusual increases… nearly simultaneous with a solar flare…” “…may have been caused by charged particles actually being emitted by the Sun…”

3. The Sun is the most energetic particle accelerator in the solar system:- Ions up to ~ 10s of GeV - Electrons up to ~100s of MeVAcceleration occurs in transient energy releases, in two (!) processes:- Large Solar Flares, in the lower corona - Fast Coronal Mass Ejections (CMEs), in the inner heliosphere, ~2-40 solar radii

4. Bastille Day 2000 Solar Flare

6. 23 July 2002 X4.8 Flare(Lin et al 2003) Thermal Plasma ~3x107 K Accelerated Electrons ~10 keV to >10s MeV Accelerated Ions ~1 to >100s of MeV

7. SPECTROSCOPY Solar Flare Spectrum hot loop Thermal Bremsstrahlung T = 2 x 107 K HXR footpoints T = 4 x 107 K photosphere Nonthermal Bremsstrahlung Π0Decay Positron and Nuclear Gamma-Ray lines g-rays  soft X-rays hard X-rays  RHESSI Energy Coverage 

10. Imaging spectroscopy

12. Krucker & Lin 2004

13. Bc t1 vin vin HXR source motions in magnetic reconnection models ? vin = coronal inflow velocity Bc = coronal magnetic field strength vfp = HXR footpoint velocity Bfp = magnetic field strength in HXR footpoint ~ photospheric value vin Bc = vfpBfp e- e- Bfp HXR HXR photosphere t2 vin vin ? e- e- HXR HXR vfp vfp

15. Velocity-HXR flux correlation Rough correlation between v and HXR flux dF = B v a dt Reconnection rate dF/dt= B v a ~ 2x1018 Mx/s E = vB ~ 5 kV/m v= velocity B= magnetic field strength a=footpoint diameter

16. g-ray imaging with RHESSI (Hurford et al. 2003, 2006) • Before RHESSI, no imaging in the g-ray range available • RHESSI g-ray imaging at 35” and 180” resolution (compared to 2” for HXRs, i.e. electrons) • Low photon statistics: integration over total flare duration needed • 2.2MeV line is best candidate low density p+ p+ g-ray footpoints? high density photosphere Where are the g-ray footpoints relative to the HXR footpoints?

17. Protons vs Electrons>~30 MeV p (2.223 MeV n-capture line)> 0.2 MeV e (0.2-0.3 MeV bremsstrahlung X-rays)e & p separated by ~104 km, but close to flare ribbons

18. Energetics – 23 July 2002 Flare • Accelerated Electrons: > ~2 x 1031 ergs ~3 x 1028 ergs/s = ~3 x 1035 (~50 keV) electrons/s for ~600s • Accelerated Ions (>2.5 MeV) : ~ 1031 ergs ~ 1028 ergs/s = ~1033 (~10 MeV) protons/s for ~1000s • Thermal Plasma: ~ 1031 ergs + losses • dE/dt = ~5x1028 ergs/s energy release rate for ~1000s

22. Tylka & Lee, 2006

23. Large (L)SEP events- tens/year at solar maximum - >10 MeV protons (small e/p ratio) - Normal coronal composition (but sometimes 3He & Fe/O enhanced) - Normal coronal charge states, Fe+10 (but sometimes enhanced ) - SEPs seen over >~100º of solar longitude - associated with: - Fast Coronal Mass Ejections (CMEs) - Large flares (but sometimes missing) - Gradual (hours) soft X-ray bursts (also called Gradual SEP events) Acceleration by fast CME driven shock wave in the inner heliosphere, 2-40 solar radii

24. Mewaldt et al 2005

25. (Mewaldt et al. 2004)

26. Mewaldt et al, 2005If these SEPs are accelerated by CME-driven shocks, they use a significant fraction of the CME kinetic energy (up to 20%)(see also Emslie et   al. 2004).

27. Tycho Supernova Remnant X-ray picture from Chandra

28. Diffusive shock acceleration: rg >> d u2 u1 shock compression R = u1/u2 Compressive discontinuity of the plasma flow leads to acceleration of particles reflecting at both sides of the discontinuity: diffusive shock acceleration (1st order Fermi) 1st order acceleration Δp~ (u/v) p where u = u1-u2 in the shock rest frame

30. Gopalswamy et al. 2004

31. January 20, 2005 SEP event Very hard spectrum Very short time to maximum intensity (30 min) (from Mewaldt et al. 2005)

32. 2002 Aug 03, X1.0 SHS 2004 Sep 19, M1.9 SHH

33. “soft-hard-soft” (SHS) vs. “soft-hard-harder” (SHH) Power law spectrum: (non-thermal HXR spectral behavior during flares) lower gamma value = flatter, ‘harder’ spectrum

34. HXR Emission SHS behavior: (more common) SHH behavior: (~15-20% of flares) time

35. Results SHH? • 60 of the 84 events had determinable spectral behavior and SEP occurrence • 23 of 60 had only partial observations and no SHH, finally leaving 37 events

36. October 27, 2002 size CME velocity ~2000 km/s very large source (>200 arcsec) expanding and rising motion

37. October 27, 2002 size CME velocity ~2000 km/s very large source (>200 arcsec) expanding and rising motion 300”

38. October 27, 2002 size CME velocity ~2000 km/s very large source (>200 arcsec) expanding and rising motion HXR emission from electrons in magnetic structures related to coronal massejections. ~400 km/s speed of CME front ~ 2000 km/s 300” ~800 km/s filament behind ~ 1000 km/s

39. X-ray spectrum 14 MK, low EM (1e46 cm-3)  density ~108 cm-3 relatively hard/flat spectrum (g~3.3) extending down to ~10 keV Number of non-thermal electrons are 10% of number of thermal electrons.

40. NASA Solar Probe + ESA Solar Orbiter Solar Sentinels

42. Protons >30 MeV(2.223 MeV Line Fluence, corrected for limb darkening)(Shih et al 2009) GOES Soft X-ray Peak flux

43. Cliver et al, 1994

44. Discussion of models • Drake et al. • extended acc. region • all electrons are acc. • power law distribution • 1b~1 stops contraction • 1b~1 stops acceleration turbulence (e.g. Liu et al. 2007) Contracting islands (Drake et al. 2006) time evolution given by acceleration and escape.

46. Gradual SEP event with 3He (Mason, Mazur, & Dwyer, 1999)

47. Tylka & Lee, 2006

49. Tylka & Lee 2006

50. Zurbuchen 2004