This is only likely to be useful if the source list is a standard XMM EPIC source list product, since the task looks for columns with names SCTS and BG_MAP. Note also that the environment variable SAS_CCF must point to a valid CCF for this style to work.
For this setting of radiusstyle, the size of each radius is scaled from the brightness of the source. An elliptical locus is obtained at which the source rate per pixel (which is, remember, not truly point-like but spread out over the PSF) decreases to some given fraction of the background rate. The fraction is specified by the parameter bkgfraction. If withellipse=`yes', this ellipse is drawn, but if withellipse=`no', a circle of radius equal to the larger semi-axis is drawn.
It should be noted that the PSF used in this routine is only approximately correct. You should not attempt to extract quantitative information from the resulting circles/ellipses.
