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

2. Flares Used Genoa RHESSI Workshop, 2 to 5 September, 20092 18 flares from Schmahl et al. (2007, Sol. Phys. 240, 241,) Well-separated double sources above 25 keV.

3. Image Reconstruction Modified Techniques used: – Visibility Forward Fit (VFF) – Clean – MEM_NJIT – Pixon 3 Genoa RHESSI Workshop, 2 to 5 September, 2009

4. Clean Det. 1 - 9 Det. 3 - 9Det. 1 - 9 PixonMEM_NJITVFF Techniques Compared Genoa RHESSI Workshop, 2 to 5 September, 2009 4

5. July 23, 2002 (00:41:00-00:42:00, 50-100 keV) 5 Genoa RHESSI Workshop, 2 to 5 September, 2009 Clean, J.MEM_NJIT VFF Pixon

6. 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 6 Genoa RHESSI Workshop, 2 to 5 September, 2009

7. Techniques Compared Genoa RHESSI Workshop, 2 to 5 September, 2009 7

8. Techniques Compared Genoa RHESSI Workshop, 2 to 5 September, 2009 8

9. Flux Comparisons Genoa RHESSI Workshop, 2 to 5 September, 2009 9

10. Major/Minor Axes Genoa RHESSI Workshop, 2 to 5 September, 2009 10

11. Orientation Angle Genoa RHESSI Workshop, 2 to 5 September, 2009 11

12. RHESSI/TRACE Overlay Genoa RHESSI Workshop, 2 to 5 September, 2009 12 Trace 171 Å Offset: X + 6” Y – 16” RHESSI 50 to 100 keV Contours: 5, 10, & 50% Black: Clean components White: Pixon Yellow: VFF

13. Genoa RHESSI Workshop, 2 to 5 September, 2009 13 Major Axis FWHM Minor Axis FWHM Arcseconds

14. VFF Flux Overestimate Genoa RHESSI Workshop, 2 to 5 September, 2009 14 An X value differing from unity suggests that the two-source model assumed in VFF is not consistent with the observations.

15. 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. Genoa RHESSI Workshop, 2 to 5 September, 2009 15