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Making the image (Deconvolution (Maximum entropy method (lagrangian…
Making the image
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Self calibration
Suppose set of observed visibiities and a model of the source which when FT'd gives model visibilities
Factorise complex gain of each telescope as gi, gj
Find gi, which solve maths, as well as possible
Replace observed visibilities with new ones, repeat
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Legitimate?
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Yes, because free parameters constraint
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Summary of uv limits
n telescopes, B=0.5n(n-1)
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VLA coverage dense, so snapshot gives reasonably good map
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Aliasing
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cures
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"guarding" FT over bigger area than I(x,y) so no images to be folded back
Phase referencing
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Require
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Close to source (looking through same bit of atmosphere) generally need within a few degrees at few GHz closer at >10GHz or <1GHz
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