attempts to detect x-ray albedo
DESCRIPTION
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). SourceS Source heighth Scattering pointP Subsource pointQ Distance P to Qr QSP θ Sun centerC Sun’s radiusR - PowerPoint PPT PresentationTRANSCRIPT
Attempts to DetectX-ray Albedo
Brian DennisNASA GSFC
Albedo GeometryBrown, J. C. , Van Beek, H. F., and McClymont, A. N. Astron. & Astrophys. 41, 395 (1975)
Source SSource height hScattering point PSubsource point QDistance P to Q rQSP θSun center CSun’s radius RDirection to Earth
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)
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.
Albedo Fraction vs. X-ray Energy
Albedo flux assuming isotropic emission• Peaks between 30 and 50 keV• Greater for flatter spectra
Simulated DataCLEAN Image
Source Alone
Cross-section through single sourceCount-rate vs. roll angle for all 9 detectors
Red: simulated dataBlack: predicted from CLEAN image
Simulated DataCLEAN Image
Source + Albedo
Cross-section through source
Clean doesn’t see the albedo wings Count-rate vs. roll angle for all 9 detectorsRed: simulated data
Black: predicted from CLEAN image
Source Alone
Simulated DataPixon Image
Count-rate vs. roll angle for detectors 1 - 7Red: simulated data
Black: predicted from pixon image
Cross section through source
Pixon does see the albedo wings
Simulated DataPixon – Circular Source + Albedo
Simulated FlareLongitude = 80
Color: simulated flare + albedoContours: Pixon Image
Simulated Flare - Longitude = 80
Color: simulated flare + albedoContours: MEM_NJIT Image
Flux contour of sourceGreen: original sourceRed: MEM_NJIT image
Disc Flare6 Nov. 2004
Possible compact source + albedo patchAltitude = 2 – 3 Mm
Disc Flare – Early Impulsive Emission2 June 2002
Note double HXR footpoint sources. Possible symmetric wings around each source.
Limb Flare20 Feb. 2002
Possible compact source + albedo patchEvidence for foreshortening???
Limb Flare21 April 2002
Note two footpoint HXR sources along TRACE 195Å ribbons and extended coronal HXR source(s) above the limb.
Limb Flare21 April 2002
Note more intense wings closer to the limb.
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 AlbedoRHESSI Science Nugget #119 (2009)
Schmahl and Hurford (2002)
Schmahl and
Hurford (2002)
Cumulative flux vs. radius (r)
Schmahl, and
Hurford, 2009,
RHESSI Science Nugget
#119
Flare on 10 April 2002Schmahl and Hurford, 2009, RHESSI Science Nugget #119
Schmahland
Hurford 2009
RHESSI Science Nugget
#119Detector # + position angle/180
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.
Clean Images10 April 2002 12:30 UT
Detector #6 Effect
Detectors 4, 5, 7, 8, 9Detectors 4, 5, 6, 8, 9
Visibility Correction Factors10 April 2002
Clean Image – det. 3, 4, 5, 7, 8, 9Is there an albedo patch?
1% contour level
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
Pixon Image – no stacker10 April 2002 12:30 UT
Pixon Image – stacker on10 April 2002 12:30 UT
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.
Mean electron flux spectraPhoton spectra
Solid lines – without albedo correctionDashed lines – with albedo correction
Albedo Detection - Statistical?• Kasparova et al. A&A, 466, 705 (2007)• Kasparova (2008) RHESSI Science Nugget #74
Anisotropy of RHESSI hard X-ray emission
Observed distributions Corrected for albedo
Solid lines – limb eventsDashed lines – disc center events
Spectral index Spectral index
Albedo Imaging?Schmahl and Hurford (2002, 2009) report
detection of extended HXR sources.
Possible Explanations1. Albedo patch2. Extended coronal source(s)3. Extended footpoint(s) along ribbons4. 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,
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.
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