IMAGE ARTIFACT REMOVAL
You may have noticed some odd looking image artifacts like the dark line running through the nebula, and the black spot with light lines stretching out from either side. These are not actually part of the source, they are instrumental artifacts that will need to be carefully removed without introducing new artifacts.

We know that the central black dot is actually the source of the most intense X-rays in the image; so intense that the detector was not able to accurately record the light coming from that region and instead was saturated to the point that there is no useful data, hence the “black hole.” We can simply, but carefully, replace the black in this region with white, to indicate the most intense light in the image. The light lines extending from this central region are “readout streaks” created by residual X-ray photons streaking across the detector as the image is transferred from the CCD. You would see similar artifacts on your own digital cameras, or cell phone cameras when they are exposed to bright pinpoint sources of light, like the sun (do not stare directly at the sun). These lines can be removed by using GIMP’s handy Healing Tool which is designed to repair image irregularities. To use it, select it in the Toolbox and then CTRL-click a region of the image near the artifact to define the source pixels, then click on the artifact itself and drag across.

A SPLASH OF COLOR
As a broadband image, you would typically apply a single gradient map of color to the image to show X-ray intensity. To apply color to your layer, go to Colors>Colorize. Sweeping the Hue bar left to right will cycle through the spectrum of colors available to you. Choose what you like and hit OK.

FINISHING TOUCHES
Your image is essentially done at this point and any further adjustments are a matter of personal taste. For example, you may want to do one last levels adjustment to enhance image contrast. You can do this via GIMP’s Curves adjustment in Colors>Curves. Further tweaks to the image color can be made using Colors>Color Balance to suit your taste.