Spectroscopybelow ~20 keV

Brian Dennis

RHESSI/NESSI III

3/30 – 4/01/2005

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The Promise

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Thermal SXR Spectra

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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.

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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.

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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.

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Equivalent-width Variations

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

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Equivalent Width vs. T

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RHESSI/RESIK Comparison

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

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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.

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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.

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Noise below 6 keV

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Noise at end of data gaps

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Lower rates at end of data gaps

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Detector 5 is cleaner

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Detector #6 has the problem

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Fe : Fe/Ni Flux Ratio vs. T

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Fe : Fe/Ni Flux Ratio vs. T

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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.