How Well Do Fits to RHESSI Hard X-Ray Spectra Determine the Electron Distribution Function?

1. How Well Do Fits toRHESSI Hard X-Ray Spectra Determine theElectron Distribution Function? Gordon D. Holman(NASA/GSFC)andLinhui Sui(CUA & NASA/GSFC)

2. The following four slides show fits to a RHESSI flare spectrum. The first shows a model photon spectrum fit to the data. The others show the thick-target bremsstrahlung from a model electron density distribution fit to the data.

3. Double Power-Law Photon SpectrumFebruary 20, 2002 (11:06:10 – 11:06:24 UT) RHESSI Flare • Thermal T = 15 MK EM = 2.6  1048 cm-3 • Nonthermal Low = 3.3 EBreak = 56 keV High = 4.4 F50 keV = 0.6

4. Double Power-Law Electron DistributionFebruary 20, 2002 (11:06:10 – 11:06:24 UT) RHESSI Flare • Thermal T = 16 MK EM = 2.4  1048 cm-3 • Nonthermal Low = 4.4 EBreak = 100 keV High = 5.5 nA = 4.6  1025 cm-1

5. Power-Law Electron Distribution with a High-Energy CutoffFebruary 20, 2002 (11:06:10 – 11:06:24 UT) RHESSI Flare • Thermal T = 16 MK EM = 2.4  1048 cm-3 • Nonthermal  = 4.5 ECutoff = 224 keV nA = 4.9  1025 cm-1

6. Power-Law Electron Distribution with a Low-Energy CutoffFebruary 20, 2002 (11:06:10 – 11:06:24 UT) RHESSI Flare • Thermal T = 40 MK EM = 4.6  1046 cm-3 • Nonthermal  = 5.3 ECutoff = 47 keV nA = 1.2  1024 cm-1

7. Conclusions • There is no unique fit to the RHESSI hard x-ray spectral data • RHESSI spectra cannot be uniquely inverted • There is not a sharp break in the photon spectrum • Fits to RHESSI spectra rule out some models and constrain others

8. References • Analysis of the 2002 February 20 Flare: Sui, L., Holman, G., Dennis, B. R., Krucker, S., Schwartz, R. A., and Tolbert, K., Solar Physics, in press, 2002.http://hesperia.gsfc.nasa.gov/hessi/presentations/first_modling_RHESSI_solar_physics.pdf • Thick-target bremsstrahlung code:RHESSI Flare Modeling Software Web Pagehttp://hesperia.gsfc.nasa.gov/hessi/modelware.htm