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Procedure for extending uv-limit of potential GMRT phase calibraters

Neeraj Gupta and Sanjay Bhatnagar
N.C.R.A., Pune
NCRA Technical Report

Abstract:

The Ionosphere above the GMRT is relatively more turbulent compared to the northern latitudes, requiring the phase calibraters to be close to the target field in the sky. The VLA P-band calibrater list provides a list of compact sources which can be used as phase calibraters at low frequencies. Many of these sources are resolved at longer baselines or at lower frequencies (or both) and hence are not good phase calibraters for the GMRT. We therefore need a list of sources which cover the sky more uniformly for the GMRT and can be used as phase calibraters. However since unresolved sources are difficult to find at low frequencies and at GMRT resolutions, we need to build a database of image-plane models of compact sources. In conjunction with these image-plane models, even moderately resolved sources can be used as phase calibraters.

In this report, we describe a scheme we used to iteratively build an image-plane model of a Galactic plane calibrater ($ J1829+487$), which is resolved at baselines $ >2K\lambda$ for GMRT at P-band. With this model, we show that the uv-range of this source is extended from 2K$ \lambda$ to $ \sim 25K\lambda$. This procedure can be used for other sources to build the above mentioned database of image-plane models. Since building this database involves a large amount of repetitive but useful work, we also explore the possibility of building a (semi-) automated software (pipeline?) which implements this scheme. A grading scheme to grade the derived image plane models and the effective range of the projected baseline lengths for which such a model is applicable is also proposed.




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Next: Introduction
Sanjay Bhatnagar 2003-10-17