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Sizes of Hard X-ray Footpoints
Brian DennisRick Pernak (CUA)
NASA GSFC
Flares Used
Genoa RHESSI Workshop, 2 to 5 September, 2009 2
18 flares from Schmahl et al. (2007, Sol. Phys. 240, 241,)
Well-separated double sources above 25 keV.
Image Reconstruction
Modified Techniques used:– Visibility Forward Fit (VFF)– Clean– MEM_NJIT– Pixon
3Genoa RHESSI Workshop, 2 to 5 September, 2009
Clean
Det. 1 - 9
Det. 3 - 9 Det. 1 - 9 Det. 1 - 9
Pixon MEM_NJIT VFF
Techniques Compared
Genoa RHESSI Workshop, 2 to 5 September, 2009 4
July 23, 2002 (00:41:00-00:42:00, 50-100 keV)
5Genoa RHESSI Workshop, 2 to 5 September, 2009
Clean, J. MEM_NJIT
VFFPixon
Modifications• Clean
– Use Clean Components– Define square “source regions”– Calc. sigmas and orientation angles– Define a new 3σ (elliptical region)– Recalculate source parameters
• MEM_NJIT and Pixon– Fit a 2D Gaussians to each source– Define 3σ elliptical region– Calculate source parameters
6Genoa RHESSI Workshop, 2 to 5 September, 2009
Techniques Compared
Genoa RHESSI Workshop, 2 to 5 September, 2009
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Techniques Compared
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Flux Comparisons
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Major/Minor Axes
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Orientation Angle
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RHESSI/TRACE Overlay
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Trace 171 ÅOffset: X + 6” Y – 16”
RHESSI50 to 100 keV
Contours: 5, 10, & 50%Black: Clean componentsWhite: PixonYellow: VFF
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Major Axis FWHM Minor Axis FWHM
Arcseconds Arcseconds
VFF Flux Overestimate
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An X value differing from unity suggests that the two-source model assumed in VFF is not consistent with the observations.
Conclusions• Techniques give comparable results for simple
double sources.• VFF can overestimate source flux.• Clean components give similar detail to Pixon.• Minor axis of most footpoint sources not
resolved at the 4” level.• Line source along flare ribbon better
approximation than elliptical Gaussian.
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