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How big are Hard X-ray Sources ---- Really?

How big are Hard X-ray Sources ---- Really?. Brian Dennis GSFC. Objectives. Determine real HXR source sizes Compare image reconstruction algorithms Establish objective procedures Analyze many flares Obtain source size distributions vs. Energy Flare intensity. Motivation. SCIENTIFIC

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How big are Hard X-ray Sources ---- Really?

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  1. How big are Hard X-ray Sources----Really? Brian Dennis GSFC

  2. Objectives • Determine real HXR source sizes • Compare image reconstruction algorithms • Establish objective procedures • Analyze many flares • Obtain source size distributions vs. • Energy • Flare intensity Brian Dennis GSFC

  3. Motivation SCIENTIFIC • Thermal SXR source area  volume volume + EM  density density + T + filling factor  thermal energy • HXR footpoint area + spectrum  electron flux density • Footpoint asymmetry  magnetic field asymmetry INSTRUMENTAL • Refine RHESSI imaging capabilities • Establish requirements for future HXR imagers: • STIX on Solar Orbiter • XRI on Solar Sentinels Brian Dennis GSFC

  4. METHOD FOR DETERMINING SIZES, POSITIONS & FLUXES Thanks to Ed Schmahl Don't use CLEAN OR MEM or PIXON Use FORWARD FIT with VISIBILITIES REASONS: Old algorithms don't weight size sensitivity properly Better to find the closest fit to the calibrated visibilities of a specific model (e.g. Gaussians + albedo) Select energy and time range with good S/N Compute visibility using SSW tools Run vis_fwdfit with 8-10 parameters Brian Dennis GSFC RHESSI WORKSHOP, MEUDON, 2006 APRIL 5-8

  5. WHAT DOES VIS_FWDFIT DO? Visibility amplitudes (crosses) are fit by a model black curve) Residuals (squares) Brian Dennis GSFC RHESSI WORKSHOP, MEUDON, 2006 APRIL 5-8

  6. RESULTS (1) FWHM= 4.1,3.6 FLUX= 21.4, 20.9 Brian Dennis GSFC RHESSI WORKSHOP, MEUDON, 2006 APRIL 5-8

  7. Source Sizes vs. EnergyThanks to Rick Pernakhttp://hesperia.gsfc.nasa.gov/~pernak/ Brian Dennis GSFC

  8. Image ComparisonsPernak et al. (2006) poster Brian Dennis GSFC

  9. MEM_NJIT CLEAN (d4 – 8) PIXON 30 October 200416:23:48 to 16:24:48 UT CLEAN images Natural weighting Detectors 1 - 9 TF = 1 D3 - 9 TF = 2 Brian Dennis GSFC

  10. 30 Oct. 2004Forward-Fitwith stackerThanks to Richard Schwartz Source sigmas: 1.1 & 1.0 arcsec. Brian Dennis GSFC

  11. 30 October 200416:23:48 to 16:24:48 UT MEM_NJIT VIS_FF Brian Dennis GSFC

  12. VIS_FF30 October 200416:23:48 to 16:24:48 UT RChisq = 15 Brian Dennis GSFC

  13. Brian Dennis GSFC

  14. Brian Dennis GSFC

  15. CLEAN Image, TF = 1 6 - 12 & 30 – 40 keVNatural weightingTF = 2 CLEAN Images Brian Dennis GSFC

  16. 30 – 40 keVUniform weightingTF = 23x3 boxcar smoothed CLEAN & Pixon Images Pixon ImageColor stretched Brian Dennis GSFC

  17. Clean & Pixon Images Brian Dennis GSFC

  18. Pixon Images Unsmoothed Boxcar smoothed3x3 pixels Brian Dennis GSFC

  19. VIS_FF 2 circular sources Brian Dennis GSFC

  20. Peak roll angles for grid 4 30” 2xFWHM = 24” Brian Dennis GSFC

  21. Ellipse - FWHM = 14” eccentricity = 0.97 Circle – FWHM = 6.8” Brian Dennis GSFC

  22. Ellipse – FWHM = 15” eccentricity = 0.75, PA = 110Circle – FWHM = 4.3” Brian Dennis GSFC

  23. Ellipse – FWHM = 5.6”, eccentricity 0.75, PA = 110Circle – FWHM = 4.5” Brian Dennis GSFC

  24. Conclusions • Always make CLEAN images first • Detectors 1 – 9 above ~25 keV • Natural weighting, test factor = 1, 2 or ∞ • Uniform weighting for compact sources • Use “media mode” - don’t add residuals • Use Pixon for extended sources • Boxcar smooth image • Use VIS_FF • Only if one or two clear compact sources • Use elliptical sources • Check chi-squared values for each detector • Include albedo • Investigate poor fits to detector 1 & 2 visibilities Brian Dennis GSFC

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