Figure caption: The GRB happened in a distant galaxy. Around the position of the GRB on the sky was a "halo" caused by X-rays from the initial burst scattered off layers of dust in our Galaxy, much in the same way as fog scatters the light from a car's headlights. The X-rays scattered by larger angles travel along a slightly longer path between the dust and the Earth. The speed of light is constant and so the X-rays travelling the longer distance reach us slightly later. This means there is a delay - we see the X-rays scattered at smaller angles first. This is why the halo rings seem to expand - not because anything is actually "moving" but because there is a time delay between seeing the X-rays that are scattered by smaller angles (which we see as a smaller ring) and those scattered by larger angles (larger ring).
This figure is also available in PS or PDF formats formats.
Maintained by Simon Vaughan
(sav2 at star. le. ac. uk)
Last updated: 26/01/2004
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