Weekly Report 24Sep2010

From RHESSI Wiki

Pixon Images with Detector Sensitivity Corrections from Visibility Forward Fit

The following was done by creating an image of the 5 arcsec source near the limb with an albedo contribution using the visibility forward fit algorithm. A single elliptical source was used as the model. The corrections to the detector sensitivities generated by visibility forward fit were then used with the Pixon algorithm to create a Pixon image from the same eventlist.

The following plot shows a fit to the visibilities generated by visibility forward fit for an elliptical source.

A plot of the visibilities generated from the data set with the fit to those visibilities using the visibility forward fit algorithm.

The fit to the visibilities shown above was used to create the reconstructed image. The C statistics for the reconstructed image are shown in the table below, along with the total C statistic just below the table.

Total C Statistic : 163.983

From the table above we can see that when constructing the image using visibility forward fit, the best image has very large C statistics. This may be due to the fact that only a single elliptical source was used to create the image. The original data also contains an extended albedo source which was not imaged by visibility forward fit. I am testing this by trying to create an image with two sources, one for the compact elliptical source and one for the extended source. So far using the combination of sources has not yielded a good fit because the parameters in the fit to the extended source are reaching their allowed limits causing no actual image to be made. I'm going to try to fix this using my knowledge of the original data set to create an image using zero iterations but good starting parameters to see if I can get an estimate of the C statistic.

The plot below shows the profile in the Heliocentric X direction of the visibility forward fit image and the original data map. the original data map has been scaled so the peak matches the peak of the visibility forward fit image.

The visibility forward fit profile along the Heliocentric X direction along with the profile for the original data map.

Total C Statistic: 1.13950