Institute of Astronomy, Radio Astronomy and Plasma Physics Group

1. Flare Electron Acceleration Arnold Benz Institute of Astronomy, Radio Astronomy and Plasma Physics Group EidgenössischeTechnische Hochschule Zürich Swiss Federal Institute of Technology, Zürich

2. 1. RHESSI Observations Spectral evolution of flares

3. non-thermal thermal RHESSI two component fits: T, EM γ, F35

4. spectral index flux Grigis & B.

5. P. Grigis

7. P. Grigis

8. Battaglia et al. 2005

9. < C2 Δ ● ● Δ Δ > C2 Battaglia & B., 2005

10. FHXR─ γ Relation • "Pivot" point at about 9 ± 3 keV (soft-hard-soft) • Consistent with constant acceleration rate above threshold energy (13.9 keV) • Consistent with constant total power in particles above threshold energy (13.6 keV) • Consistent with stochastic acceleration beyond 18.1 keV • Inconsistent with pure "statistical flare" scenario

11. Diffusion by stochastic wave turbulence ( ( (  E1/2   f(E) f(E) t+zE E E1/2+t ( ( ( D E f(E) = coll aW 1/L Assume steady state => Bessel equation Solution: f(E) = C E -d + 1/2 Kd(E) Approximation for d << dc: f(E)  fo E- fo  (WL) 7/8anti-   (WL) -1/2correlation ! } Benz 1977

12. Approximate further, eliminate WL and get for observed HXR flux: (1/2 + 1/2[1 +(+3/2)]1/2)2 FHXR C [( - 1)(+3/2)]2 log FHXR  Brown & Loran, 1985

13. 2. RHESSI –Phoenix Observations

14. Type III radio emission in 201 X-ray flares >C5.0 Pulsations Diffuse cont. Narrowband spikes Type IV TypeI before rise peak decay after Hfbroadband (gyro-synchrotron)

15. Meter-Decimeter Radio Patternsof X-ray selected flares A Standard 129 B Just IIIm 8 C Afterglows 20 D No Radio 34 E Type I 10

16. Standard

17. Standard M1.1 irreg. pulsation 25 – 50 keV 50 – 100 keV

18. Standard M1.1 reversed drift IIIm 25 – 50 keV 50 – 100 keV

19. irregular pulsation Standard M1.1 decimetric narrowband spikes 25 – 50 keV 50 – 100 keV

20. Standard C7.7 IIIdm irreg.pulsation hf continuum 6 – 12 keV 12 – 25 keV 25 – 50 keV

21. Just IIIm

22. Just IIIm C7.9 6 – 12 keV 12 – 25 keV 25 – 50 keV

23. Just IIIm C7.9 6 – 12 keV 12 – 25 keV 25 – 50 keV

24. Type IV and DCIM "Afterglows"

25. Phoenix-2 Radio spectrum type IV decimetric pulsations drifting structure gyro- synchrotron GOES Class X17 gyro- synchrotron

26. Phoenix-2 Radio spectrum decimetric pulsations decimetric patch

27. Type IV DCIM

28. Afterglows M2.3 IIIm and hf continuum 3 – 6 keV 6 – 12 keV narrowband spikes 12 – 25 keV

29. Afterglows M2.3 patch 3 – 6 keV 6 – 12 keV regular dm pulsation 12 – 25 keV

30. Afterglows M5.0 6 – 12 keV 12 – 25 keV 25 – 50 keV regular dm pulsations 100 – 300 keV 50 – 100 keV

31. No Radio

32. radio-quiet flare 6 – 12 keV 12 – 25 keV 25 – 50 keV 50 – 100 keV GOES class M1.0

33. no-radio flaresFlares C5.0 – C9.9 22 %Flares > M1.0 12 % All flares > C5.0 17 % Two possible interpretations: 1. Small flares have less radio emission (sensitivity effect) 2. Large flare have more associated processes ("large flare syndrom", suggesting indirect connection)

34. Standard: reconnection at 1 and 2 Just IIIm: reconnection at 2 Type IV: reconnection at 2 after 1 Noise storm: reconnection at 2 Radio-quiet:: reconnection at 1 2 C B 1 A

35. Standard: reconnection at 1 and 2 Just IIIm: reconnection at 2 Type IV: reconnection at 2 after 1 Noise storm: reconnection at 2 Radio-quiet:: reconnection at 1 2 A 1

36. Summary on HXR - Radio Correlations • Hard X-ray and radio emissions of flares are relatively independent. • 17% of >C5.0 flares have no coherent radio emissions (22% if type I excluded). • Many type IIIm have no hard X-ray emission. • Correlation is often poor, suggesting multiple acceleration sites for "standard flare pattern" and "afterglows". • Multiple reconnection may also interprete "big flare syndrom".

37. Where are electrons accelerated?- often in more than one site (independent signatures) • - most IIIm (and SEDs) have only very weak hard X-ray • emission (possibly high-coronal flares). • 2. How are they accelerated? • - Violent acceleration processes are excluded. • - If acceleration signature, why not close X-ray • correlation? • - Radio type IV and DCIM indicate processes long • after flare • 3. If loop-top, why this large number? • - loop-top may be secondary acceleration site Conclusions

38. Observational Constraints on Flare Particle Acceleration • Absence of radio emission in 17% of flares does not support violent acceleration processes, such as single shocks or single DC fields. • Consistent with heating processes (bulk energization). • RHESSI observations show that flares start with soft non-thermal spectrum. In the beginning it is difficult to distinguish from a thermal spectrum (γ ≈ 8). 4. The spectrum of non-thermal electrons gets harder with flux of non- thermal electrons both in time during one flare, as well as with peak flare flux (Battaglia et al. 2005). 5. The evidence supports stochastic bulk energization to hot thermal distribution and, if driven enough with power-law wings.

41. Standard C9.0 IIIm irregular dm pulsation narrowband spikes reversed drift IIIdm 6 – 12 keV 12 – 25 keV 25 - 50 keV

42. Standard X1.6 II IIIdm HF cont. 6 – 12 keV IIIdm IIIdm 12 – 25 keV 25 – 50 keV

43. Irregular pulsation Standard C9.7 OVSA

44. Standard C6.5 irreg.pulsation 6 – 12 keV 12 – 25 keV

45. Standard RHESSI Christe & Krucker

46. Just IIIm C8.0 6 – 12 keV 12 – 25 keV

47. Type I C7.3 6 – 12 keV 12 – 25 keV

48. Type I