Weekly Report 19Nov2010 26Nov2010

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Pixon Albedo Imaging

Using Eduard Kontar's simulated eventlist files, Pixon Images were created for a compact circular gaussian source with an albedo contribution near disk center, and near the limb. The following parameters were used for each image:

The following plots are extensions of the plots from the previous report.

The plot below shows the gaussian model of the compact source (orange),the original data map with the minimum and maximum value at each radial distance (Black), the Pixon image with the minimum and maximum value at each radial distance (Purple), and the clean image with the minimum and maximum value at each radial distance (Cyan)for a source near disk center.

Original Data Map (Black), Pixon Map (Purple), Clean Map (Cyan), Model Gaussian (orange) for a source near the disk center

The gaussian model falls off as we would expect the flux to fall in a circular gaussian. For 2 arcsec the model and the map are consistent, after this point the model falls off much more sharply, while the map shows a falloff that is not gaussian. The pixon image shows a tight envelope around the compact source, as does the clean image. As we move into the region where the albedo is present clean falls off in the same manner as the original map. The envelope around the the average of the flux for clean widens immediately after the compact source but then remains relatively constant. The pixon image immediately goes from a tight envelope around the compact source to a wider envelope in the region of the albedo. The size of the envelope remains constant radially but the average moves up and down in an unpredictable manner. For instance at approximately 3.5 arcsec from the peak of the compact source pixon images what appears to be a 'pileup' of flux. At the edges of the image the flux does not drop away to zero but seems to level off.


The plot below shows the gaussian model of the compact source (orange),the original data map with the minimum and maximum value at each radial distance (Black), the Pixon image with the minimum and maximum value at each radial distance (Purple), and the clean image with the minimum and maximum value at each radial distance (Cyan) for a source near the limb.

Original Data Map (Black), Pixon Map (Purple), Clean Map (Cyan), Model Gaussian (orange) for a source near the limb)

In the case of the source near the limb the averages of each the original data, the clean image, and the pixon image fall off in a similar manner to the averages near the disk center. There is more variation at any given point with the average moving up and down, but the trend is similar. However, looking at the min and max for the original data map, and the imaging algorithms the foreshortening effect shows up. There is a much larger envelope around the average for each method. The min and the max are much more widely separated. The min falls off to zero more rapidly and the max is higher in each case, at a given radial distance. This is what we would expect in the case of foreshortening. Foreshortening creates an asymmetry in the source and the albedo. The plots below clearly show this asymmetry.

The following plot shows the the average and the min and max for the clean images near the disk center and near the limb.

The clean profile for an image near disk center (Cyan), and near the limb (Purple), with the minimum and maximum values also shown for each radial distance.

The purple plot shows the values for the image near disk center. The cyan plot shows the image near the limb. The image near the disk center shows a tight envelope around the average value for the extent of the compact source. As we move radially away from the compact source the envelope around the average flux gets wider but remains symmetric. Looking at the cyan plot, the average flux away from the compact source falls of slightly more than near disk center, but with a similar slope. It does not fall off in the same smooth fashion as the image near disk center, showing higher and lower fluxes as it approaches the edge of image causing a 'spiky' pattern. The more interesting aspect is the behavior of the min and max traces. They envelope formed by these around the average is wider than in the case of the image at disk center, with a sharper falloff for the minimum compared to the maximum. This is the expected behavior when foreshortening is present.The minimum values at a given radial distance away from the disk center will be smaller than the values toward the disk center. This means the minimum value and maximum values should differ more than in a case with radial symmetry.


The following plot shows the the average and the min and max for the clean images near the disk center and near the limb.

The pixon profile for an image near disk center (Cyan), and near the limb (Purple), with the minimum and maximum values also shown for each radial distance.

RHESSI Image Test - Clean v. Pixon

The original source map (background), with the pixon contours(Blue) for an image using detectors 1 to 4, and clean contours (Green) for an image using detectors 1 and 2.
The profile in the Heliocentric X direction through the center of the map. The profile for the original map is black, the clean profile is red, and the green profile is red.

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