Correction for rotation of the primary beam

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Correction for rotation of the primary beam

Postby luke » Wed May 17, 2017 10:17 pm

In most sources of information on the primary beam for the ATCA, it is assumed that the primary beam has rotational symmetry.
For example, .

In practice, this is not quite true. This can cause a problem with sources at the edge of the primary beam having amplitude variation with time.
This there a way to correct for this within MIRIAD or CASA? This would be quite useful, especially for bright sources at the edge of the beam.
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Re: Correction for rotation of the primary beam

Postby Mark.Wieringa » Thu Jun 15, 2017 12:13 pm

Hi Luke,

You are quite right, in wide fields this can be an obvious problem. The solution is to use A-projection in CASA, however that requires a 2D model of the ATCA beam and its variation with frequency, which unfortunately we don't have. An added complication is that the effect differs in the X and Y polarization. We've attempted to come up with model based on beam measurements but due to rapid variation with frequency (possibly due to standing waves) it hasn't resulted in a consistent model we can use.
The alternative solution is to use peeling, this will work if the offending sources are strong enough for selfcal.


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