The effects of cosmic ray filtering on low intensity X-ray CCD data

Various methods exist to filter cosmic rays from X-ray CCD images with weak X-ray spectra. Distortions of the characteristics of a spectral profile such as peak centroid and relative integrated peak intensities must be kept to a minimum. Optimum methods are those minimising error bars and widths on the final centroid determination and on relative intensities which remain consistent with the widths for unfiltered data. A cluster method, a linear correlation method and a combination of both were examined using H-like Ti collected at the NIST EBIT. The cluster method is a strong filter but appears to distort centroids and relative intensities. The linear correlation method filters less and distorts less. The strongest filtering is to use both yielding the highest signal-to-noise while enhancing apparent distortions. All methods appear fairly robust. Strong cosmic-ray filters with minimal distortion of X-ray spectra can increase the precision of X-ray CCD measurements and enhance the resulting physical insight.