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

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

Above-the-Loop Coronal Source Ohyama & Shibata 1996 Yohkoh/SXT observations: Yohkoh/SXT observations: out-flowing speed of km/s out-flowing speed of 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

Three RHESSI Flares M3.7 M1.2 M keV keV April 14-15, 2002 April 15 April 16 Sui & Holman 2003 Sui et al Sui 2005

Three RHESSI Flares (I) M1.2 April 15

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

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

Revisit the Yohkoh event Ohyama & Shibata 1996

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

Energy Distributions Sui & Holman 2003

8-10 keV keV keV footpoints Temperature Distribution

14-16 keV keV keV 8-10 keV keV keV footpoints

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

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

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

Three RHESSI Flares (II) April 16 April 16, keV 6-12 keV keV

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

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

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

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

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

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

A New Type of Coronal Source? C9.4 flare on 2002/06/02 TRACE keV 6-12 keV keV keV 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

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

Loops Seen with RHESSI 2002/04/15

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

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) keV 6-12 keV Sui & Holman 2003

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

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

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

Looptop Downward Motion (04/16)

More events Veronig et al /11/03 X3.9 flare 2002/09/20 M keV

Downward Motion in Other Wavelength keV Radio Observation (NoRH) EUV Observation (TRACE) Li & Gan (2005) Li & Gan (2006)

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

Statistical Results 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)

Interpretation of Loop Contraction 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

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

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

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

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 keV) C9.4 flare Sui et al. 2006

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

3-6 keV 6-12 keV keV keV Moving Down Moving Up Source Motion Sui et al. 2006

3-6 keV 6-12 keV keV keV Moving Down Moving Up keV Source Motion

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

3-6 keV 6-12 keV keV keV Downward moving source is nonthermal thick-target emission Energy Distribution

3-6 keV 6-12 keV keV keV Power-law at Low Energies Nonthermal iron line excitation?

3-6 keV C1.2 flare More Events

10-16 keV

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

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