1. Spectroscopy below ~20 keV Brian Dennis RHESSI/NESSI III 3/30 – 4/01/2005

2. 2 The Promise

3. 3 Thermal SXR Spectra

4. 4 The Potential F-F & F-B continuum gives T and EM. Flux ratio of 6.7 : ~8 keV line complexes gives T and EM. Centroid energy gives T. Equivalent width gives Fe abundance. Deviations give multi-temperature info. Ratio of thermal to nonthermal energy.

5. 5 Problems Detector effective areas differ by >20%. Energy offset function of count rate. Attenuation uncertainties. Enhancement at ~10 keV from unknown source – tungsten L-shell lines at 8 & 10 keV? Excess counts at <5 keV. Uncertain detector resolution. Uncertain non-solar background level.

6. 6 Difference in Detector Responses Figure Differences in spectra for detectors 1 and 4 for the same 1-minute time period, during Apr. 21, 2002 flare.

7. 7 Equivalent-width Variations Figure.Fe-line equivalent widths determined with different detectors for the same time intervals during the 26 April 2003 flare.

8. 8 Equivalent Width vs. T

9. 9 RHESSI/RESIK Comparison Figure.RHESSI, RESIK, and GOES spectra for the same time interval showing the overlap at 3 keV.

10. 10 Feature at ~10 keV Tungsten L-shell lines at 8 & 10 keV –Compton scattering in passive low-Z materials allowing these lines to leak “around” the attenuators –direct exposure to L-shell lines from “neighboring” grids. Empirical fit with a narrow Gaussian.

11. 11 Excess Counts Below ~10 keV K-escape fraction seems accurate. Possible leakage of flux around attenuators. Counts after saturating pulses and ends of data gaps.

12. 12

13. 13 Noise below 6 keV

14. 14 Noise at end of data gaps

15. 15 Lower rates at end of data gaps

16. 16 Detector 5 is cleaner

17. 17 Detector #6 has the problem

18. 18

19. 19

20. 20

21. 21

22. 22

23. 23 Fe : Fe/Ni Flux Ratio vs. T

24. 24 Fe : Fe/Ni Flux Ratio vs. T

25. 25 Action Items Detector sensitivity calibration –Using Crab data –Use flare decay observations Attenuation calibration –Use data pre- and post-attenuator changes –Compare with RESIK, XSM, & SOXS Investigate possible energy offset after reset pulses. Implement energy offset vs. count rate – will visibilities help? Implement Chianti v. 5. Investigate tungsten L-shell lines. Add line-complex template option to OSPEX.