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Low-Energy Coronal Sources Observed with RHESSI

Low-Energy Coronal Sources Observed with RHESSI. Linhui Sui (CUA / NASA GSFC). Outline. Above-the-loop coronal sources Loop-top coronal sources Inside-loop coronal sources Summary. Above-the-Loop Coronal Source. Yohkoh/SXT observations: out-flowing speed of 50-400 km/s

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Low-Energy Coronal Sources Observed with RHESSI

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

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

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

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

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

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

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

  8. Revisit the Yohkoh event Ohyama & Shibata 1996

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

  10. Energy Distributions Sui & Holman 2003

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

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

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

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

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

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

  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) 140 km/s Implication: Current sheet formation Sui 2005

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

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

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

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

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

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

  25. Loops Seen with RHESSI 2002/04/15

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

  27. Looptop Downward Motion (04/15) • 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 6-12 keV 25-50 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. Upward Speed Correlates with HXR Loop growth speed correlates with the hard X-ray flux Loop growth delayed by 20~40 s Hloop / vevaporation = 2 X104 / 300~800 = 20~60 s Sui et al. 2004

  30. Analogy of Footpoint Motion 2003/07/23 X4.8 flareKrucker et al. 2003 • Equivalent to correlations between Vfootpoint(Krucker et al. 2003) or Vfootpoint × Bphotosphere (Qiu et al. 2004) and HXR flux.

  31. Looptop Downward Motion (04/16)

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

  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 (Holman et al. 2005) • 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.

  36. Interpretation of Loop Contraction 10-25 keV • Source moving horizontally along arcade (no) • Current sheet formation (Sui & Holman 2003, Sui et al. 2004) • 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…

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

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

  40. Early Impulsive Flares Sui et al. 2006 C9.6 Flare C9.4 flare • 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)

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

  42. Source Motion 3-6 keV 6-12 keV 12-25 keV 25-50 keV Moving Down 2 3 1 3-6 keV Moving Up 5 6 4 7 8 9 Sui et al. 2006

  43. Source Motion 3-6 keV 6-12 keV 12-25 keV 25-50 keV Moving Down 6-7 keV 2 3 2 3 1 1 3-6 keV Moving Up 5 6 5 6 4 4 7 8 9 7 8 9

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

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

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

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

  48. More Events 10-16 keV

  49. Interpretations for the Motions 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

  50. Summary 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 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)

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