1. Low-Energy Coronal Sources Observed with RHESSI Linhui Sui (CUA / NASA GSFC)

2. Outline Above-the-loop coronal sources Above-the-loop coronal sources Loop-top coronal sources Loop-top coronal sources Inside-loop coronal sources Inside-loop coronal sources Summary Summary

3. Above-the-Loop Coronal Source Ohyama & Shibata 1996 Yohkoh/SXT observations: Yohkoh/SXT observations: out-flowing speed of 50-400 km/s out-flowing speed of 50-400 km/s jet or twisted loop jet or twisted loop Interpretations: Interpretations: flux rope flux rope Shibata et al. 1995, Ohyama & Shibata 1996, Kim et al. 2005

4. Three RHESSI Flares M3.7 M1.2 M2.5 6-12 keV 25-50 keV April 14-15, 2002 April 15 April 16 Sui & Holman 2003 Sui et al. 2004 Sui 2005

5. Three RHESSI Flares (I) M1.2 April 15

6. 10 – 25 keV Impulsive rise HXR Peak 300 km/s

7. 10 – 25 keV Impulsive rise 25-50 keV HXR Peak 300 km/s

8. Revisit the Yohkoh event Ohyama & Shibata 1996

9. 10-12 keV 12-14 keV14-16 keV Energy Distribution (2002/04/15 23:11 – 23:11:20 UT) Sui & Holman 2003

10. Energy Distributions Sui & Holman 2003

11. 8-10 keV 12-14 keV 16-20 keV footpoints Temperature Distribution

12. 14-16 keV 12-14 keV 10-12 keV 8-10 keV 12-14 keV 16-20 keV footpoints

13. Associated CME C2 04/16 02:26 C3 04/16 06:18 (V~ 300 km/s) Sui et al. 2005

14. Coronal Source and CME coronal source CME front Sui et al. 2005

15. High Coronal X-ray Sources Tearing Mode Instability? 23:13:40 UT 23:16:40 UT Sui et al. 2005

16. Three RHESSI Flares (II) April 16 April 16, 2002 12-25 keV 6-12 keV 25-50 keV

17. RHESSI Images (6-12 keV) Step 1 (rise phase): Coronal source connected to the loop.

18. RHESSI Images (6-12 keV) Step 2 (impulsive phase): The coronal source separates from the loop and move outward (it may stay stationary for a while) Implication: Current sheet formation 140 km/s Sui 2005

19. 6-8 keV8-10 keV10-12 keV Energy Distribution (2002/04/16 13:04:20 – 13:05:20 UT) Sui 2005

20. Rising Flux Rope & CME Goff et al. 2005 RHESSI + TRACE 13:50 UT

21. Impulsive rise 25-50 keV Three RHESSI Flares (III) Flare of April 14-15 (12-25 keV) Sui et al. 2004

22. More Events 2003/11/03 X3.9 Veronig et al. 2005

23. A New Type of Coronal Source? C9.4 flare on 2002/06/02 TRACE 195 3-6 keV 6-12 keV 12-25 keV 25-50 keV 50-100 keV The coronal source was located at the cusp region. Is this Low-energy Masuda source? Particle acceleration is more efficient before cusp was formed!! Sui et al. 2006

24. Rising Flare Loops Yohkoh/SXT Loop height increase with time is the foundation of the current flare standard model. Svestka et al. 1995 2.4 km/s

25. Loops Seen with RHESSI 2002/04/15

26. Looptop Downward Motion (04/15) 25-50 keV 6-12 keV Sui & Holman 2003

27. Altitude decrease: 24% (6-12 keV) 33% (12-25 keV) Falling speed: 15 km/s 23 km/s Rising speed: 15 km/s 21 km/s Looptop Downward Motion (04/15) 25-50 keV 6-12 keV Sui & Holman 2003

28. Looptop Downward Motion (04/14) Altitude Decrease: 13% (6-12 keV) 20% (12-25 keV) Falling Speed: 10 km/s 11 km/s Sui et al. 2004

29. Loop growth speed correlates with the hard X-ray flux Loop growth delayed by 20~40 s H loop / v evaporation = 2 X10 4 / 300~800 = 20~60 s Upward Speed Correlates with HXR Sui et al. 2004

30. Analogy of Footpoint Motion Equivalent to correlations between V footpoint (Krucker et al. 2003) or V footpoint × B photosphere (Qiu et al. 2004) and HXR flux. 2003/07/23 X4.8 flare Krucker et al. 2003

31. Looptop Downward Motion (04/16)

32. More events Veronig et al.2005 2003/11/03 X3.9 flare 2002/09/20 M1.2 25-50 keV

33. Downward Motion in Other Wavelength 10-25 keV Radio Observation (NoRH) EUV Observation (TRACE) Li & Gan (2005) Li & Gan (2006)

34. Converging Hα Kernels and downward motion (Ji et al. 2006) Converging Hα kernels Converging footpoints Downward moving looptops

35. Statistical Results 10-25 keV Of the 88 limb flares that had an identifiable loop structure:  79% of the sample showed upward expansion.  66% showed downward contraction followed by upward expansion.  Therefore, 84% of the loops showing upward expansion were preceded by downward contraction. (Holman et al. 2005)

36. Interpretation of Loop Contraction 10-25 keV 1.Source moving horizontally along arcade (no) 2.Current sheet formation (Sui & Holman 2003, Sui et al. 2004) 3.Magnetic shrinkage ( Svestka et al.1987 ) 4. Collapsing magnetic trap (Veronig et al. 2005) 5. Magnetic Implosion (Hudson 2000) reduced

37. Coronal Sources Inside Loops Some background information… Some background information…

38. Typical Flares in X-rays 2002/04/15 M1.2

39. Preheating Troubles:  hiding evidence for low-energy cutoffs  losing low-energy electrons (Emslie 2003, Galloway et al. 2005)  hiding weak coronal sources Plasma Pre-heating 2002/04/15 M1.2 Thermal Nonthermal

40. C9.6 Flare Early Impulsive Flares  Hard X-ray flux (> 25 keV) increases before the soft X-ray flux rises significantly.  160 early impulsive flares in 2002 (~25% flares with 25-50 keV) C9.4 flare Sui et al. 2006

41. One Early Impulsive Flare GOES 3-6 keV 6-12 keV 12-25 keV 25-50 keV Sui et al. 2006

42. 3-6 keV 6-12 keV 25-50 keV 12-25 keV 1 23 4 56 789 Moving Down Moving Up Source Motion Sui et al. 2006

43. 3-6 keV 6-12 keV 25-50 keV 12-25 keV 1 23 4 56 789 Moving Down Moving Up 1 23 4 56 789 6-7 keV Source Motion

44. Source Altitue 700 km/s 500 km/s 340 km/s 45 km/s

45. 3-6 keV 6-12 keV 25-50 keV 12-25 keV Downward moving source is nonthermal thick-target emission Energy Distribution

46. 3-6 keV 6-12 keV 25-50 keV 12-25 keV Power-law at Low Energies Nonthermal iron line excitation?

47. 3-6 keV C1.2 flare More Events

48. 10-16 keV

49. For downward motion: plasma density decrease inside loops (X) spectral hardening low-energy cutoff increasing For upward motion: chromospheric evaporation spectral softening low-energy cutoff decreasing Interpretations for the Motions

50. 1. The appearance of the above X-loop coronal source and its evolution may suggest existence of a large-scale of current sheet. (why not more?) 2. The looptop downward motion earlier in the flare could be the result of formation of the current sheet. (need simulations) 3. The correlation of the 3. The correlation of the loop growth speed and HXR flux support the standard flare model. (more events) 4. Multiple plasma blobs appeared along a line above the loop may suggest elongation of the current sheet. (need more events!) 5. Downward and upward motions of coronal sources inside of loops are direct evidence for electron transport along the loop. Electron spectral evolution may explain both motions. (simulation is ongoing) Summary