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Characterizing Thermal and Non-Thermal Electron Populations in Solar Flares Using RHESSI

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.

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Characterizing Thermal and Non-Thermal Electron Populations in Solar Flares Using RHESSI

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  1. Characterizing Thermal and Non-Thermal Electron Populations in Solar Flares Using RHESSI Amir Caspi1,2, Säm Krucker2, Robert P. Lin1,2 1 Department of Physics, University of California, Berkeley, CA 94720 2 Space Sciences Laboratory, University of California, Berkeley, CA 94720

  2. Motivation AAS/SPD Meeting

  3. 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 AAS/SPD Meeting

  4. 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) AAS/SPD Meeting

  5. Fe & Fe/Ni line complexes • Differing temperature profiles of line complexes suggests ratio is unique determination of isothermal temperature (Phillips 2004) AAS/SPD Meeting

  6. 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 AAS/SPD Meeting

  7. Flux ratio vs. Temperature AAS/SPD Meeting

  8. Flux ratio vs. Temperature AAS/SPD Meeting

  9. Flux ratio vs. Temperature AAS/SPD Meeting

  10. Flux ratio vs. Temperature AAS/SPD Meeting

  11. Flux ratio vs. Temperature AAS/SPD Meeting

  12. 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? AAS/SPD Meeting

  13. 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 AAS/SPD Meeting

  14. Centroids of emission • Clear displacement between centroids of lower energy and higher energy emission AAS/SPD Meeting

  15. 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 AAS/SPD Meeting

  16. 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 AAS/SPD Meeting

  17. Count Spectrum AAS/SPD Meeting

  18. Flux ratio vs. Temperature AAS/SPD Meeting

  19. Flux ratio vs. Temperature AAS/SPD Meeting

  20. Flare location/size AAS/SPD Meeting

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