You may be wondering how astrophysicists go from the lightcurves and spectra mentioned in the previous sections to the pretty images in the sidebar on the left of this page. It all comes down to photon counts and where those photons hit the detector.
For example, the following images were made by counting the number of photons with energies 0.25 keV, 0.5 keV and 1.5 keV (respectively) that hit the detector in spatial bins. Then an image is made by color coding each bin by the number of photons detected in the energy range under consideration - the lighter the color, the more photons that were counted at that location.
¼ keV image
¾ keV image
1.5 keV image
These images are projections of the whole sky, kind of like stretching out globe of the Earth. The black streaks are places where there is no data, not actual X-ray features. The images are composed of many, many observations over years by the ROSAT X-ray telescope. I obtained these images from the Skyview web site.
