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Q:
In the Chandra image of XTE J1118+480, are we observing the
center spectral diagonal line as a line or are we seeing the
line as the outside edge of a flat plane?
A:
The features in the image of XTE J1118+480 are, alas,
instrumental artifacts produced by the Low Energy Transmission
Grating. This instrument is an assembly of finely constructed
gold gratings that are attached to the rear of the mirrors and
can be swung into the path of th X-rays collected by the
mirrors. In much the same way as a raindrop breaks sunlight into
the colors of the rainbow, these gratings bend or diffract the
reflected X-rays according to their energy. High-energy X-rays
are bent less than low-energy X-rays, so they strike the
detectors at different places. This is what produces the long
streaks in the image. A precise measurement of the position
where the X-ray hits the detector gives an exact measurement of
the energy of the X-ray. The grating literally sorts the X-rays
according to their energy. http://chandra.harvard.edu/about/science_instruments3.html
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