Edge-filtered X-ray images. In the top panels the X-ray 0.3–2.3 keV image was filtered with the Gaussian Gradient Magnitude (GGM) filter on scales of 8 pixels (16 arcsec; top left panel) and 4 pixels (8 arcsec; top right panel). Before filtering, point source regions were cosmetically filled using the values of random neighbouring pixels. The bottom panel has been processed by an adaptive GGM filter (using a signal to noise ratio of 32), where the scale shows the gradient as the log₁₀ change per 4 arcsec pixel.