Sizes of Hard X-ray Footpoints

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					Sizes of Hard X-ray Footpoints

           Brian Dennis
        Rick Pernak (CUA)
            NASA GSFC
                                 Flares Used
                                    18 flares from Schmahl et al.
                                    (2007, Sol. Phys. 240, 241,)

                                    Well-separated double
                                    sources above 25 keV.




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




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



                                                 Clean




                                                 Det. 1 - 9



   Pixon      MEM_NJIT                     VFF
                Genoa RHESSI Workshop, 2 to 5
                                                              4
                      September, 2009
 July 23, 2002 (00:41:00-00:42:00, 50-100 keV)

Clean, J.                                        MEM_NJIT




Pixon                                            VFF




                 Genoa RHESSI Workshop, 2 to 5
                                                       5
                       September, 2009
          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

              Genoa RHESSI Workshop, 2 to 5
                                              6
                    September, 2009
Techniques Compared




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




     Genoa RHESSI Workshop, 2 to 5
                                     8
           September, 2009
Flux Comparisons




    Genoa RHESSI Workshop, 2 to 5
                                    9
          September, 2009
Major/Minor Axes




    Genoa RHESSI Workshop, 2 to 5
                                    10
          September, 2009
Orientation Angle




    Genoa RHESSI Workshop, 2 to 5
                                    11
          September, 2009
RHESSI/TRACE Overlay

                                      Trace 171 Å
                                      Offset: X + 6” Y – 16”

                                      RHESSI
                                      50 to 100 keV

                                      Contours: 5, 10, & 50%
                                      Black: Clean components
                                      White: Pixon
                                      Yellow: VFF




      Genoa RHESSI Workshop, 2 to 5
                                                                12
            September, 2009
Major Axis FWHM                               Minor Axis FWHM




 Arcseconds                                     Arcseconds
              Genoa RHESSI Workshop, 2 to 5
                                                                13
                    September, 2009
                          VFF Flux
                        Overestimate
                  An X value differing from unity
                  suggests that the two-source model
                  assumed in VFF is not consistent with
                  the observations.




Genoa RHESSI Workshop, 2 to 5
                                                          14
      September, 2009
                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
                                                  15
                        September, 2009

				
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posted:7/25/2013
language:English
pages:15