1. Probing Electron Acceleration with X-ray Lightcurves Siming Liu University of Glasgow 9 th RHESSI Workshop, Genova, Italy, Sep. 2009

2. Flare Classification with X-ray Lightcurves 1: Single component flares 2: Flares with gradual SXRs and impulsive HXRs a): Impulsive HXR Bursts b): Extended HXR Bursts

3. Single Component Events Gradual Events Impulsive Events

4. Gradual SXRs & Impulsive HXRs Hoyng et al 1976; Liu et al. 2004, 2006; Lin et al. 2003 Impulsive HXR Bursts Extended HXR Bursts

5. Basic Questions Gradual (low-energies) is Thermal? YES by definition Impulsive (not necessarily high - energies) is Non-thermal? YES by definition Their Relation? Neupert Effect

6. Neupert Effect Veronig et al. 2005 Physical process for the low-energy cutoff unclear

7. Elementary Events Sui et al. 2007

8. 1: Energy Dissipation (b 0, t 0 =l e /v A ) 2: Plasma Heating, Particle Acceleration, and Transport 3: Chromospheric Evaporation Impulsive Phase Processes

9. Energy Dissipation & Evaporation

10. Electron Acceleration

11. Electron Distribution at the Looptop Liu et al. 2009

12. Evolution of Elementary Event Liu et al. 2009

13. Impulsive Well-Observed Bursts Liu et al. 2003, 2006

14. Sub-second scale features are likely caused by transport and plasma physics processes Liu et al. 2009 Multiple Loops

15. Extended Bursts Lin et al. 2003

16. Statistical Studies Battaglia & Benz 2005 2.3-4.2 4.2-5.6 5.6-8.3

17. Statistical Studies Veronig et al. 2002

18. Statistical Studies Krucker et al. 2007; Liu et al. 2008

19. Conclusions The details of the electron acceleration can be studied in the context of stochastic acceleration by turbulent plasma waves for flares with a few relatively simple impulsive HXR bursts. The large scale dynamical processes play more important roles in extended HXR bursts. Statistical results of many bursts can be used to constrain the acceleration model.

20. flare ribbons chromosphere UV loops (10 K) 5 H-alpha loops (10 K) 4 X-ray loops (10 K) 7 magnetic field lines conduction front reconnection inflow current sheet Superhot hard X-ray region (>10 K) 8 (standard flare configuration adapted from Forbes & Acton, 1996) Extended HXR Bursts

21. Extended Bursts Warren & Doschek 2004

22. Asymmetry Kontar et al. 2005

23. EUV at 171A (by TRACE) H-alpha 6563A (by BBSO) soft X-ray 1-8A (GOES) hard X-ray 20 keV (Yohkoh) hard X-ray 100 keV (Yohkoh) microwave 6.6 GHz (OVSA) Most flares have impulsive non-thermal and gradual thermal emission components

24. Measuring the electron acceleration efficiency?

25. Measuring the electron acceleration efficiency? Model the thermal X-ray emission and find the component correlated with the non-thermal X-ray emission. Challenging, if not impossible!

26. The particle transport, chromspheric evaporation, and radiative cooling processes are difficult to model for complex flares. If the particle acceleration process is universal for all flares, as we usually assume, we should study the particle acceleration efficiency with relatively simple flares.

27. Goals TheoryHow does the efficiency depend on properties of the background plasma: B, T, n, size of the flaring region, energy release rate, … ObservationsMeasure (constrain) the efficiency Explore its dependence on the emission characteristics: spectral features, flux density, size of the emission region, variation time scale, … Particle Acceleration Efficiency measures the energy partition between the emerging thermal and non-thermal particles.

28. Energy Release Event Turbulence Heating Acceleration Radiation (non-thermal) RADIATION (thermal) Radiation (non-thermal) Heating Turbulence Acceleration IMPULSIVE GRADUAL

29. Particle Distribution Function E E f(E)

30. fit ( th. +nth. )  = - 4.5 3-4 keV 6-9 keV 13-20 keV 20-30 keV GOES 1-8 A observed 7.8 GHz 9.4 GHz 11.8 GHz 14.8 GHz  = - 3.0  = - 3.1  = - 4.4 Hard X-ray microwave (Qiu et al. 2005) Measuring the electron acceleration efficiency?

31. Particle Distribution Function

32. Multi-Processes: reconnection geometry wave/turbulence generation and transport, particle generation and transport plasma evaporation and cooling

33. Theoretical Considerations Solar flares are multi-scale phenomena in terms of energy, duration, and spatial scale, so are likely the particle acceleration events.

34. Thermal vs. Non-thermal ThermalNon-thermal TheoryParticle DistributionMaxwellianPower-law EnergyLowHigh InteractionsCoulomb Collisions Particle-Field Collisionless Observ ations Emission Properties Temporal Spectral Spatial Energetics Gradual Narrow Extended? ? Impulsive Broad Compact? ? Particle Acceleration Efficiency measures the energy partition between the emerging thermal and non-thermal particles.