A direction-dependent framework for visibility plane mosaicing and primary beam correction

ABSTRACT With the increasing sensitivity of modern radio interferometers, it has become important to image objects larger than the field of view while optimizing sensitivity and image fidelity. We present a coherent visibility plane direction-dependent imaging, calibration, and mosaicing framework. Our simulations and application to real MeerKAT data show that this joint deconvolution and primary beam correction approach, coupled with direction-dependent calibration, allows for deeper mosaics with greater fidelity and increased accuracy of recovered flux densities and spectral indices, especially beyond the half-power beam width. Our best-case mosaic produces precise flux values within a 6 per cent uncertainty and spectral indices within 20 per cent throughout the imaged area, and is fully complete out to twice the radii and half the flux density than the image plane equivalent. The application to archival wide-band MeerKAT 1283 MHz data produces the deepest high-resolution image of the Shapley Supercluster Core, with a sensitivity of 3.6 $\mu$Jy beam−1 within the primary beam at a 7 arcsec resolution, constituting a $\sim$50 per cent increase in dynamic range over the image plane counterpart, and a fluxscale that is consistent within 10 per cent across the entire field of view. The compute time for the direction-dependent visibility plane mosaic was comparable to the sum of the times needed to perform direction-dependent calibration on the individual pointings. Our results suggest that visibility plane mosaicing with its capability for deeper deconvolution could improve the efficiency of deep and wide surveys, particularly for on-the-fly mapping and studies of low surface brightness sources, and could form the basis of future calibration pipelines for SKA-scale instruments.