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Attempts to Detect X-ray Albedo

Attempts to Detect X-ray Albedo. Brian Dennis NASA GSFC. Albedo Geometry Brown, J. C. , Van Beek, H. F., and McClymont , A. N. Astron. & Astrophys . 41, 395 (1975). Source S Source height h Scattering point P Subsource point Q Distance P to Q r QSP θ Sun center C Sun’s radius R

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Attempts to Detect X-ray Albedo

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  1. Attempts to DetectX-ray Albedo Brian Dennis NASA GSFC

  2. Albedo GeometryBrown, J. C. , Van Beek, H. F., and McClymont, A. N. Astron. & Astrophys. 41, 395 (1975) Source S Source height h Scattering point P Subsource point Q Distance P to Q r QSP θ Sun center C Sun’s radius R Direction to Earth 

  3. Albedo GeometrySource at solar disc center (L = 0) dI(θ) (counts cm-2 arcsec-2) = f I0 F1 F2 F3 F4 dI Albedo flux from point P in albedo patch θ Angle from vertical to point P (angle QSP in Figure 1) f Photospheric reflectance (~0.6 at 15 – 20 keV) I0 Primary source flux (assumed isotropic) F1 = (cos θ)-2 Inverse-square fall off from S F2 = (cos θ)-1 Projection onto plane photosphere F3 ~ 1 Compton scattering directivity F4 ~ 1 Curvature correction  dI(θ) ~ f I0 / (2 cos3θ)

  4. Albedo Patch(Kontar & Jeffries 2010) • Lower flux density (photons s-1 cm-2 arcsec-2) compared to primary source – down by factors of >10. • Impossible to image using current version of CLEAN • Should be possible to image albedo patch using pixon • Evidence for extended source using Visibilities (VIS-FF) • Geometric foreshortening close to limb. • Centroid shifted towards disc center compared to primary source.

  5. Albedo Fraction vs. X-ray Energy • Albedo flux assuming isotropic emission • Peaks between 30 and 50 keV • Greater for flatter spectra

  6. Simulated DataCLEAN Image Cross-section through single source Count-rate vs. roll angle for all 9 detectors Red: simulated data Black: predicted from CLEAN image Source Alone

  7. Simulated DataCLEAN Image Source + Albedo Cross-section through source Clean doesn’t see the albedo wings Count-rate vs. roll angle for all 9 detectors Red: simulated data Black: predicted from CLEAN image

  8. Simulated DataPixon Image Cross section through source Count-rate vs. roll angle for detectors 1 - 7 Red: simulated data Black: predicted from pixon image Source Alone

  9. Simulated DataPixon – Circular Source + Albedo Pixon does see the albedo wings

  10. Simulated FlareLongitude = 80 Color: simulated flare + albedo Contours: Pixon Image

  11. Simulated Flare - Longitude = 80 Flux contour of source Green: original source Red: MEM_NJIT image Color: simulated flare + albedo Contours: MEM_NJIT Image

  12. Disc Flare6 Nov. 2004 Possible compact source + albedo patch Altitude = 2 – 3 Mm

  13. Disc Flare – Early Impulsive Emission2 June 2002 Note double HXR footpoint sources. Possible symmetric wings around each source.

  14. Limb Flare20 Feb. 2002 Possible compact source + albedo patch Evidence for foreshortening???

  15. Limb Flare21 April 2002 Note two footpoint HXR sources along TRACE 195Å ribbons and extended coronal HXR source(s) above the limb.

  16. Limb Flare21 April 2002 Note more intense wings closer to the limb.

  17. Albedo DetectionImaging? Schmahl, E. J. and Hurford, G. J. (2002, 2009) Report detection of extended HXR sources. RHESSI Observations of the Size Scales of Solar Hard X-ray Sources Sol. Phys., 210, 273 (2002) Solar Hard X-ray Albedo RHESSI Science Nugget #119 (2009)

  18. Schmahl and Hurford (2002)

  19. Schmahl and Hurford (2002) Cumulative flux vs. radius (r)

  20. Schmahl, and Hurford, 2009, RHESSI Science Nugget #119

  21. Flare on 10 April 2002Schmahl and Hurford, 2009, RHESSI Science Nugget #119

  22. Schmahland Hurford 2009 RHESSI Science Nugget #119 Visibility Amplitude Detector # + position angle/180

  23. Schmahl and Hurford (2009) RHESSI Science Nugget #119 But, reduced chi-squared = 7. And, 15 – 20 keV and 12 – 15 keV are low energy ranges to see albedo.

  24. Clean Images10 April 2002 12:30 UTDetector #6 Effect Detectors 4, 5, 6, 8, 9 Detectors 4, 5, 7, 8, 9

  25. Visibility Correction Factors10 April 2002

  26. Clean Image – det. 3, 4, 5, 7, 8, 9Is there an albedo patch? 1% contour level

  27. UV-smooth Image – det. 345789Correction factors: 0.00,0.00,1.33,1.01,1.06,0.81,0.97,0.93,1.04 10% - lowest contour level

  28. Pixon Image – no stacker10 April 2002 12:30 UT

  29. Pixon Image – stacker on10 April 2002 12:30 UT

  30. Albedo Detection - Spectroscopy? Kontar & Brown (2006) ApJ, 653, L152. Kontar et al. (2006) A&A, 446, 1157. September 17, 2002 solar flare, 5:50:48-5:51:36 UT. Photon spectra Mean electron flux spectra Solid lines – without albedo correction Dashed lines – with albedo correction

  31. Albedo Detection - Statistical? • Kasparova et al. A&A, 466, 705 (2007) • Kasparova (2008) RHESSI Science Nugget #74 Anisotropy of RHESSI hard X-ray emission Number of events, N Observed distributions Corrected for albedo Spectral index  Spectral index  Solid lines – limb events Dashed lines – disc center events

  32. Albedo Imaging? • Schmahl and Hurford (2002, 2009) report detection of extended HXR sources. Possible Explanations • Albedo patch • Extended coronal source(s) • Extended footpoint(s) along ribbons • Instrumental Effects • Pulse pile-up • Image reconstruction technique (Visibility Forward Fit) • Detector sensitivity mismatch Schmahl, E. J. and Hurford, G., J., 2002, Sol. Phys., 210, 273. Schmahl, E. J. and Hurford, G., J., 2009, RHESSI Science Nugget #119,

  33. Conclusion • Albedo must be present unless primary source is highly asymmetric. • Simulations show that pixon image reconstruction is capable of showing albedo wings. • Wings detected in pixon images for most flares. • But origin of wings is uncertain. • No evidence of longitude foreshortening of flare sources. • Is image reconstruction capable of detecting foreshortening? • Extended sources evident from visibility amplitudes • Albedo patches? • Coronal sources? • Not certain that albedo has ever been conclusively detected from RHESSI imaging information. • Spectroscopy evidence for albedo is more compelling.

  34. Future Work • Improve detector sensitivity calibrations. • Pixon reconstructions to image albedo patches. • Correct annular sector to XY coordinates problem with compact sources. • Examine images and spectra for more flares. • Spectral analysis for consistency with imaging. • Further simulations with more realistic multiple source geometries and background rates. • Variations with longitude to reveal foreshortening and altitude effects. • Visibility Forward Fit with assumed albedo patches. • Schmahl and Hurford

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