Summary
Image reconstruction performance measures the effective blurring of the X-ray PSF due to aspect reconstruction. To search for any temporal degradation of image reconstruction performance (due primarily to warm pixels), we have analyzed aspect solution accuracy for 276 observations from the year 2000 and 79 observations from Feb-Mar 2003. We find a slight increase in the RMS centroid residuals, but not at a level which is expected to have an impact on science analysis of reconstructed X-ray images.Analysis
The plot below was created using the output of the Aspect V&V tool, which determines star centroiding residuals after removing the spacecraft dither using the aspect solution.
The upper panel shows histograms of the RMS centroid residual for all stars. The black histogram is for data from the year 2000, while red is for early 2003. There is a slight shift in the distribution, and the mean has changed from 0.060 arsec to 0.070 arcsec. (Note that the 2003 dataset has fewer data points, but I have normalized the histograms to have the same area.) The left panel shows the histogram plotted on a log scale, while the right panel uses a linear scale.
The lower panel is the same, but only shows the best (lowest RMS) star for each obsid. This plot gives a reasonable upper limit to the aspect solution uncertainty for each obsid. There is only a slight change in the distribution, and the mean has changed from 0.046 arcsec to 0.050 arcsec.
Based on these data, I would conclude that the presence of warm pixels at the current level does not noticably degrade the aspect solution accuracy, although there may be a few more outliers.
See also the Image
Reconstruction Performance page.
Tom Aldcroft Last modified: 04/29/03