1. RHESSI/NESSIE, June 2003 H.S. Hudson The RHESSI 3-10 keV spectrum H. Hudson, B. Dennis, K. Phillips, R. Schwartz, D. Smith

2. RHESSI/NESSIE, June 2003 H.S. Hudson The 3-10 keV spectrum The Fe K-shell feature dominates this spectrum. The Fe feature is unresolved, but can be measured precisely in terms of centroid and equivalent width vs time. We have made a morphological study based on empirical fits to the total-flux spectrum in a collection of shutter-out flares.

3. RHESSI/NESSIE, June 2003 H.S. Hudson An example Ge Fe

4. RHESSI/NESSIE, June 2003 H.S. Hudson Fitted spectrum

5. RHESSI/NESSIE, June 2003 H.S. Hudson Model spectra Mewe compilation (should use Chianti in future) Arnaud-Rothenflug ionization states (should use better) Default abundances (may differ)

6. RHESSI/NESSIE, June 2003 H.S. Hudson F3 F8 FE Centroid Energy Equivalent width Model spectra 5 MK 10 20 50 100

7. RHESSI/NESSIE, June 2003 H.S. Hudson Implications The Fe feature is prominent and carries diagnostic information It can be measured well in high B - low C flares, with the shutters open It can also be observed well through the thin shutter

8. RHESSI/NESSIE, June 2003 H.S. Hudson Different temperatures The centroid energy determines an ionization temperature The equivalent width determines an excitation temperature The background continuum (or GOES) determines a core temperature for the electron distribution

9. RHESSI/NESSIE, June 2003 H.S. Hudson Other diagnostics The feature may show the effects of a distributed emission measure Or it may show the effects of non-thermal particle excitation It may provide a robust handle on the Fe abundance

10. RHESSI/NESSIE, June 2003 H.S. Hudson Some morphology Time variation of Fe feature centroid energy Use F3 and F8 to get Fe feature residuals Behavior of equivalent width

11. RHESSI/NESSIE, June 2003 H.S. Hudson Broad-band channels F3 and F8 F3: 3-6.33 keV F8: 7.67-10 keV We find empirically (ie, from the time profiles) that F3 is the rough equivalent of GOES “0.5-4 A”

12. RHESSI/NESSIE, June 2003 H.S. Hudson Broad-band temperature variation GOES RHESSI F8/F3

13. RHESSI/NESSIE, June 2003 H.S. Hudson Joint variation of centroid energy and equivalent width

14. RHESSI/NESSIE, June 2003 H.S. Hudson An example of centroid energy variation with flare phase Rise phase

15. RHESSI/NESSIE, June 2003 H.S. Hudson RHESSI gain calibration at low energies as seen via Fe, not Ge

16. RHESSI/NESSIE, June 2003 H.S. Hudson Individual detector gains

17. RHESSI/NESSIE, June 2003 H.S. Hudson Conclusions We find that the Fe feature can easily be characterized with 2-sec integrations in small flares It seems to be loaded with diagnostic information never previously studied We need to worry about calibrations at better than the 0.01 keV level (only 10 eV!) There seems to be anomalous behavior in the feature equivalent width vs temperature