Characterizing Thermal and Non Thermal Electron Populations in

Characterizing Thermal and Non. Thermal Electron Populations in Solar Flares Using RHESSI Amir Caspi 1, 2, Säm Krucker 2, Robert P. Lin 1, 2 Department of Physics, University of California, Berkeley, CA 94720 2 Space Sciences Laboratory, University of California, Berkeley, CA 94720 1 July 27, 2004 RHESSI Paris Workshop

Motivation July 27, 2004 RHESSI Paris Workshop 2

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 Þ Want to determine flare energetics, heating and acceleration mechanisms July 27, 2004 RHESSI Paris Workshop 3

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) July 27, 2004 RHESSI Paris Workshop 4

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

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 July 27, 2004 RHESSI Paris Workshop 6

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

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

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

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

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

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 theory? • Why are the curves different between flares? July 27, 2004 RHESSI Paris Workshop 12

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 July 27, 2004 RHESSI Paris Workshop 13

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

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

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

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 July 27, 2004 RHESSI Paris Workshop 17

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 Þ Determine flare energetics July 27, 2004 RHESSI Paris Workshop 18

Count Spectrum July 27, 2004 RHESSI Paris Workshop 19

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

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

Flare location/size July 27, 2004 RHESSI Paris Workshop 22