1. Distinguishing Between Thermal and Non-Thermal Electron Populations in Solar Flares Using RHESSI Amir Caspi 1,2, Robert P. Lin 1,2 1 Department of Physics, University of California, Berkeley, CA 94720 2 Space Sciences Laboratory, University of California, Berkeley, CA 94720

2. May 26, 2005AGU/SPD Joint Assembly2 Questions How do we characterize the thermal electrons? –What is the temperature distribution? –How does it evolve in time? –How much energy do they contain? And non-thermal electrons? –What is the energy distribution? –What is the low-energy cutoff? –How much energy do contain/deposit?  Need to distinguish between the two populations  Difficult to do from continuum emission alone

3. May 26, 2005AGU/SPD Joint Assembly3 Difficulties with Continuum

4. May 26, 2005AGU/SPD Joint Assembly4 Comparison of lines to continuum Fe & Fe/Ni features seen in most RHESSI flares Fluxes and equiv. widths are strongly temperature- dependent (Phillips 2004) Fit spectra with thermal continuum, 2 Gaussians, & power law (if applicable) Compare line fluxes and flux ratio with continuum measurements

5. May 26, 2005AGU/SPD Joint Assembly5 Flux ratio vs. Temperature

6. May 26, 2005AGU/SPD Joint Assembly6 Flux ratio vs. Temperature

7. May 26, 2005AGU/SPD Joint Assembly7 Flux ratio vs. Temperature

8. May 26, 2005AGU/SPD Joint Assembly8 Flux ratio vs. Temperature

9. May 26, 2005AGU/SPD Joint Assembly9 23 July 2002: Pre-impulsive phase Fit equally well with or without thermal continuum! –Iron lines indicate thermal plasma must be present, but much cooler than continuum fit implies

10. May 26, 2005AGU/SPD Joint Assembly10 Emissivity vs. Temperature

11. May 26, 2005AGU/SPD Joint Assembly11 Emissivity vs. Temperature

12. May 26, 2005AGU/SPD Joint Assembly12 Emissivity vs. Temperature Possible explanations: –Ionization lag –Low-temperature plasma w/o significant line emission –Multi-thermal temperature distribution –Instrumental effects and coupled errors in multi-parameter fits –Excitation by non-thermal electrons –Incorrect assumptions about abundances and/or ionization fractions –Abundance variations during the flare … small contribution

13. May 26, 2005AGU/SPD Joint Assembly13 Flux ratio vs. Temperature

14. May 26, 2005AGU/SPD Joint Assembly14 Flux ratio vs. Temperature

15. May 26, 2005AGU/SPD Joint Assembly15 Conclusions Fe & Fe/Ni features provide another measure of thermal plasma besides continuum emission –Help reject improper fits to thermal continuum –Provide thermal information even when continuum is difficult to analyze Line/continuum relationship appears to change during flare –Suggests theory may need corrections –Initial assumptions about abundances and/or ionization fractions may be incorrect Not all flares exhibit the same line/continuum relationship –Suggests different temperature distributions –Other differences (spectral hardness, abundances) may contribute

16. EXTRA SLIDES

17. May 26, 2005AGU/SPD Joint Assembly17 Flux ratio vs. Temperature

18. May 26, 2005AGU/SPD Joint Assembly18 Flux ratio vs. Temperature

19. May 26, 2005AGU/SPD Joint Assembly19 Flux ratio vs. Temperature

20. May 26, 2005AGU/SPD Joint Assembly20 Flux ratio vs. Temperature

21. May 26, 2005AGU/SPD Joint Assembly21 Flux ratio vs. Temperature

22. May 26, 2005AGU/SPD Joint Assembly22 Emissivity vs. Temperature

23. May 26, 2005AGU/SPD Joint Assembly23 Emissivity vs. Temperature

24. May 26, 2005AGU/SPD Joint Assembly24 Emissivity vs. Temperature

25. May 26, 2005AGU/SPD Joint Assembly25 Emissivity vs. Temperature

26. May 26, 2005AGU/SPD Joint Assembly26 Emissivity vs. Temperature

27. May 26, 2005AGU/SPD Joint Assembly27 Emissivity vs. Temperature

28. May 26, 2005AGU/SPD Joint Assembly28 Emissivity vs. Temperature

29. May 26, 2005AGU/SPD Joint Assembly29 Flare location/size