Weekly Report 16Jul2010

Simulated Point source with albedo near the limb

• Using new eventlist files created by Eduard Kontar for a simulated 2arcsec source near the limb with albedo, different imaging methods were tested to the and reconstruct the data.

In the first test Pixon was used with a 64X64 pixel Field of View with .5x.5 arcsec pixels.

Pixon Contours on a background map of the actual data used to create the eventlist

The Pixon Contours do not match the point source and the albedo. Pixon creates a circular source that does not demonstrate foreshortening. The contours around the source do not lie where they do on the original map. They are deformed toward the center of the sun.

The fits to the profiles for each detector using pixon are shown below.

Profiles for each detector with the fit to the data using Pixon (no phase stacker)

The combined C statistic for all detectors was 1.05. None of the individual detectors shows a large C statistic suggesting this is a fundamental feature of the Pixon Image Reconstruction algorithm and not an issue with the data

The flux profile along a line for the Pixon image and the data map is shown below. The profiles are taken along a line parallel to the heliocentric x axis through the brightest pixel in the image. The green trace shows the profile from the original map, the red trace is the profile from the Pixon Map. The green trace was multiplied by a constant to account for the difference in the flux in a given pixel for the Pixon reconstruction as compared to the map of the original data. I've emailed Eduard to get the exact conversion, for comparisons in the plot below I've normalized the peak of the data map to the peak of the Pixon Image.

The flux profile of the pixon image in RED versus the flux profile of original data in GREEN. The Pixon image does not show the same structure as the real data

Pixon shows a smooth profile as it moves away from the source while the data contains a shoulder with a smaller peak toward the center of the sun. Changing pixon parameters (pixel size, field of view, pixon sensitivity) did not affect this difference. This may demonstrate a fundamental limitation in using pixon to image the foreshortening of the albedo near the limb.

The same test was run with Clean and MEM_NJIT algorithms. The image below shows the contours from a clean image overlaid on a background image of the original data map.

The contours from the clean image overlaid on the original data. Clean is closer to the actual source location although it does not show the foreshortening effect. Clean also shows a change in the shape of the outer contour as it attemps to image the distorted albedo.

Clean was run with a clean_beam_width_factor = 2. At the highest fluxes clean images the source as circular, it does not show the foreshortening of the actual source. At the highest contour level clean does show some deformation away from circular as it attempts to image the albedo.

The C statistics for the clean image are below: d1 = 1.00858 d2 = 0.970225 d3 = 0.982332 d4 = 1.11908 d5 = 1.04800 d6 = 1.04195 d7 = 1.05662 d8 = 0.976697 d9 = 1.09013 overall c statistic = 1.00

Once again the c statistics for each detector show a good fit to the profile for each detector.

The comparison of the flux along a line parallel to the heliocentric x axis through the brightest pixel of the source is shown below. The clean profile is in RED, the original data map profile is in GREEN.

The Clean flux profile is RED, the profile from the original data map is GREEN. Clean is once again smoother and the source appears larger than in the original image. The foreshortening effect is lost. Clean shows a shoulder in the profile but it is farther away from the source than in the original data.

Clean shows more structure than the Pixon but the source itself does not show evidence of foreshortening. There is evidence of a shoulder but not in the same location as the original data. Clean displays a better ability to model the structure of the albedo than Pixon.

Finally MEM NJIT was