spectroscopy below ~20 kev brian dennis rhessi/nessi iii 3/30 – 4/01/2005
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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.