1. Characterizing Thermal and Non- Thermal Electron Populations in Solar Flares Using RHESSI Amir Caspi 1,2, Säm Krucker 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. July 27, 2004RHESSI Paris Workshop2 Motivation

3. July 27, 2004RHESSI Paris Workshop3 Questions Is the flare isothermal? –If not, what is the temperature distribution? –Where are thermal sources located? What is the low-energy cutoff for the nonthermal emission? –Critical for energy estimates  Want to determine flare energetics, heating and acceleration mechanisms

4. July 27, 2004RHESSI Paris Workshop4 Fe & Fe/Ni line complexes Line(s) are visible in almost all RHESSI flare spectra Fluxes and equivalent width of lines are strongly temperature-dependent (Phillips 2004)

5. July 27, 2004RHESSI Paris Workshop5 Fe & Fe/Ni line complexes Differing temperature profiles of line complexes suggests ratio is unique determination of isothermal temperature (Phillips 2004)

6. July 27, 2004RHESSI Paris Workshop6 Fe & Fe/Ni line complexes Assume isothermal –Not necessarily the best fit! Single power law with low-energy cutoff 2 Gaussians to approximate Fe & Fe/Ni line complexes

7. July 27, 2004RHESSI Paris Workshop7 Flux ratio vs. Temperature

8. July 27, 2004RHESSI Paris Workshop8 Flux ratio vs. Temperature

9. July 27, 2004RHESSI Paris Workshop9 Flux ratio vs. Temperature

10. July 27, 2004RHESSI Paris Workshop10 Flux ratio vs. Temperature

11. July 27, 2004RHESSI Paris Workshop11 Flux ratio vs. Temperature

12. July 27, 2004RHESSI Paris Workshop12 More questions Well-defined correlation between Fe to Fe/Ni ratio and isothermal temperature for each flare, but… No agreement between observations and theory No agreement between individual flares! Why are observations so far from the theory? Why are the curves different between flares?

13. July 27, 2004RHESSI Paris Workshop13 Possible answer Multi-thermal distribution –Differs between flares Imaging spectroscopy would be ideal –Obtain spectra based on source location Isolate and analyze multiple thermal plasmas at different temperatures within each flare Distinguish between thermal and non-thermal sources

14. July 27, 2004RHESSI Paris Workshop14 Double-thermal flux ratio

15. July 27, 2004RHESSI Paris Workshop15 Double-thermal flux ratio

16. July 27, 2004RHESSI Paris Workshop16 Centroids of emission Clear displacement between centroids of lower energy and higher energy emission

17. July 27, 2004RHESSI Paris Workshop17 Centroids of emission Higher energy emission from higher in the looptop –Strongly implies multi-thermal distribution Centroid of Fe line complex emission consistent with high- EM, lower-T plasma lower in looptop

18. July 27, 2004RHESSI Paris Workshop18 Conclusions Observations do not agree with predictions –Multi-thermal distribution –Other variations Ongoing Work Obtain DEM to determine temperature distributions Imaging spectroscopy for spatially-separated sources, to separate thermal sources at different temperatures, and to distinguish between thermal and non-thermal sources  Determine flare energetics

19. July 27, 2004RHESSI Paris Workshop19 Count Spectrum

20. July 27, 2004RHESSI Paris Workshop20 Flux ratio vs. Temperature

21. July 27, 2004RHESSI Paris Workshop21 Flux ratio vs. Temperature

22. July 27, 2004RHESSI Paris Workshop22 Flare location/size