Sizes of Hard X-ray Footpoints Brian Dennis Rick Pernak (CUA) NASA GSFC.

Sizes of Hard X-ray Footpoints

Brian DennisRick Pernak (CUA)

NASA GSFC

Flares Used

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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

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Clean

Det. 1 - 9

Det. 3 - 9 Det. 1 - 9 Det. 1 - 9

Pixon MEM_NJIT VFF

Techniques Compared

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July 23, 2002 (00:41:00-00:42:00, 50-100 keV)

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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

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Techniques Compared

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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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