Weekly Report 23Jul2010 30Jul2010

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Weekly Report 23Jul2010 30Jul2010

Simulated Point Source with Albedo Imaged Using Forward Fit Techniques

An eventlist for a point source with albedo was created for an event near limb. As shown in the previous report various imaging techniques were used to reconstruct the RHESSI images. This report focuses on using Forward Fit Techniques to image the albedo and it's foreshortening near the limb.

VIS FWDFIT with two ellipses

Using the VIS FWDFIT Image reconstruction algorithm a point source and albedo near the limb were reconstructed using a fit with two ellipses. The background image is the data map that was used to construct the eventlist, the blue contours are the vis_fwdfit image.

The background map is the data used to create the eventlist. The blue contours are the vis_fwdfit reconstruction with two ellipses as the initial guess at the shape of the image.

The specifications for the image are: Time: 2-Sep-2002 00:07:54 - 00:07:58 Energy Range: 25keV - 50keV Detectors: All Front Segments Total Counts: 3.28 x 10^4 counts

The image was created using information about the approximate location of the point source and the albedo along with their sizes from the original data map as the initial guesses for the two ellipse fit. The model of the point source is off center and larger than the original source. The albedo is offset and from the original and extended along the Heliocentric Y Axis. The eccentricity of the ellipse modeling the albedo is extremely high. Attempts to create this image using different detector combination's and different fluxes and locations of the initial guesses for the ellipses caused the algorithm to fail. Removing detectors 1 and 2 caused a complete breakdown in the ability of the algorithm to image the albedo component. In those cases the point source could still be imaged with varying degrees of accuracy but the albedo could not be imaged at all.

The profile along a line parallel to the Heliocentric X Axis. The red trace is the original data map profile. The green trace shows the profile of the reconstructed image using vis_fwdfit with two ellipses as an initial model.


VIS FWDFIT with a single ellipse - Comparison of visibilities at different angles

Datavisfwdfit.jpg
Visfwdfitprofcstatangle0.jpg
The visibility data for the simulated point source with albedo near the limb along with the fit to the visibilities for a fit with an angle of 0 degrees
Visfwdfitprof90.jpg
The visibility data for the simulated point source with albedo near the limb along with the fit to the visibilities for a fit with an angle of 90 degrees. Notice the phase difference between the fits.

FWDFIT showing a single compact source

The background image shows the data map of a point source with albedo near the limb. The blue contours show a reconstructed image using FWDFIT with a single elliptical source. The green contours show a reconstructed image using FWDFIT with two elliptical sources. All other parameters are the same for the two images
The individual light curves for each detector are shown along with the fit using FWDFIT with a single elliptical gaussian source. The C statistics for each detector are shown.
The individual light curves for each detector are shown along with the fit using FWDFIT with two elliptical gaussian sources. The C statistics for each detector are shown.
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