Low-Energy Coronal Sources Low-Energy Coronal Sources Observed with RHESSIObserved with RHESSI

Linhui Sui (CUA / NASA GSFC)Linhui Sui (CUA / NASA GSFC)

OutlineOutline

Above-the-loop coronal sourcesAbove-the-loop coronal sources

Loop-top coronal sourcesLoop-top coronal sources

Inside-loop coronal sourcesInside-loop coronal sources

SummarySummary

Above-the-Loop Coronal SourceAbove-the-Loop Coronal Source

Ohyama & Shibata 1996

• Yohkoh/SXT observations:Yohkoh/SXT observations: out-flowing speed of 50-400 km/sout-flowing speed of 50-400 km/s jet or twisted loopjet or twisted loop

Interpretations:Interpretations: flux ropeflux rope

Shibata et al. 1995, Ohyama & Shibata 1996, Kim et al. 2005

Three RHESSI FlaresThree RHESSI FlaresM3.7

M1.2

M2.5

6-12 keV

25-50 keV

April 14-15, 2002

April 15

April 16Sui & Holman 2003Sui et al. 2004Sui 2005

Three RHESSI Flares (I)Three RHESSI Flares (I)

M1.2

April 15

10 – 25 keV Impulsive rise

HXR Peak

300 km/s

10 – 25 keV Impulsive rise

25-50 keV

HXR Peak

300 km/s

Revisit the Yohkoh eventRevisit the Yohkoh event Ohyama & Shibata 1996

10-12 keV 12-14 keV 14-16 keV

Energy DistributionEnergy Distribution (2002/04/15 23:11 – 23:11:20 UT)(2002/04/15 23:11 – 23:11:20 UT)

Sui & Holman 2003

Energy DistributionsEnergy Distributions

Sui & Holman 2003

8-10 keV

12-14 keV 16-20 keV

footpoints

Temperature DistributionTemperature Distribution

Temperature DistributionTemperature Distribution

14-16 keV 12-14 keV10-12 keV

8-10 keV

12-14 keV 16-20 keV

footpoints

Associated CMEAssociated CME

C2 04/16 02:26 C3 04/16 06:18

(V~ 300 km/s)

Sui et al. 2005

Coronal Source and CMECoronal Source and CME

coronal source

CME front

Sui et al. 2005

High Coronal X-ray SourcesHigh Coronal X-ray SourcesTearing Mode Instability?

23:13:40 UT 23:16:40 UT

Sui et al. 2005

Three RHESSI Flares (II)Three RHESSI Flares (II)

April 16

April 16, 2002

12-25 keV

6-12 keV

25-50 keV

RHESSI ImagesRHESSI Images

(6-12 keV)(6-12 keV)

Step 1 (rise phase): Coronal source connected to the loop.

RHESSI ImagesRHESSI Images

(6-12 keV)(6-12 keV)

Step 2 (impulsive phase): The coronal source separates from the loopand move outward (it maystay stationary for a while)

Implication:Current sheet formation

140 km/s

Sui 2005

6-8 keV 8-10 keV 10-12 keV

Energy DistributionEnergy Distribution (2002/04/16 13:04:20 – 13:05:20 UT)(2002/04/16 13:04:20 – 13:05:20 UT)

Sui 2005

Rising Flux RopeRising Flux Rope& CME & CME

Goff et al. 2005

RHESSI + TRACE

13:50 UT

Impulsive rise 25-50 keV

Three RHESSI Flares (III)Three RHESSI Flares (III)

Flare of April 14-15Flare of April 14-15(12-25 keV)

Sui et al. 2004

More EventsMore Events

2003/11/03 X3.9

Veronig et al. 2005

A New Type of Coronal Source?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 keV50-100 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

Rising Flare LoopsRising 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

Loops Seen with RHESSILoops Seen with RHESSI

2002/04/15

Looptop Downward Motion (04/15)Looptop Downward Motion (04/15)

25-50 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)Looptop Downward Motion (04/15)

25-50 keV

6-12 keV

Sui & Holman 2003

Looptop Downward Motion (04/14)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

Hloop / vevaporation

= 2 X104 / 300~800= 20~60 s

Upward Speed Correlates with HXRUpward Speed Correlates with HXR

Sui et al. 2004

Analogy of Footpoint MotionAnalogy of Footpoint Motion

• Equivalent to correlations between Vfootpoint (Krucker et al. 2003) or Vfootpoint × Bphotosphere (Qiu et al. 2004) and HXR flux.

2003/07/23 X4.8 flare Krucker et al. 2003

Looptop Downward Motion (04/16)Looptop Downward Motion (04/16)

More eventsMore events

Veronig et al.2005

2003/11/03 X3.9 flare

2002/09/20 M1.2

25-50 keV

Downward Motion in Other WavelengthDownward Motion in Other Wavelength10-25 keV

Radio Observation (NoRH) EUV Observation (TRACE)

Li & Gan (2005) Li & Gan (2006)

Converging HConverging Hαα Kernels and Kernels and downward motion downward motion

(Ji et al. 2006)

Converging Hα kernels

Converging footpoints

Downward moving looptops

Statistical ResultsStatistical Results10-25 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)

Interpretation of Loop ContractionInterpretation of Loop Contraction10-25 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)

V dVB )8/( 2 reduced

Coronal Sources Inside LoopsCoronal Sources Inside Loops

Some background information…Some background information…

Typical Flares in X-raysTypical 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-heatingPlasma Pre-heating

2002/04/15 M1.2

Thermal

Nonthermal

C9.6 Flare

Early Impulsive FlaresEarly 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 flareSui et al. 2006

One Early Impulsive FlareOne Early Impulsive Flare

GOES

3-6 keV

6-12 keV

12-25 keV25-50 keV

Sui et al. 2006

3-6 keV

3-6 keV

6-12 keV

25-50 keV

12-25 keV

1 2 3

4 5 6

7 8 9

Moving Down

Moving Up

Source MotionSource Motion

Sui et al. 2006

3-6 keV

3-6 keV

6-12 keV

25-50 keV

12-25 keV

1 2 3

4 5 6

7 8 9

Moving Down

Moving Up

1 2 3

4 5 6

7 8 9

6-7 keV

Source MotionSource Motion

Source AltitueSource Altitue

700 km/s

500 km/s

340 km/s

45 km/s

3-6 keV

6-12 keV

25-50 keV

12-25 keV

Downward moving source is nonthermal thick-target emission

Energy DistributionEnergy Distribution

3-6 keV

6-12 keV

25-50 keV

12-25 keV

Power-law at Low EnergiesPower-law at Low Energies

Nonthermal iron line excitation?

3-6 keV

C1.2 flare

More EventsMore Events

More EventsMore 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 MotionsInterpretations 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)

SummarySummary