Simulations of imaging extended sources using the GMRT and the U-GMRT: Implications to observing strategies

Abstract

Astrophysical sources such as radio halos and relics in galaxy clusters, supernova remnants and radio galaxies have angular sizes from a few to several $10$s of arcminutes. In radio interferometric imaging of such sources, the largest angular size of the source that can be imaged is limited by the shortest projected baseline towards the source. It is essential to determine the limitations of the recovery of the extended features on various angular scales in order to interpret the radio image. We simulated observations of a model extended source of Gaussian shape with the Giant Metrewave Radio Telescope (GMRT) using Common Astronomy Software Applications (CASA). The recovery in flux density and in morphology of the model source was quantified in a variety of observing cases with changing source properties and the uv-coverage. If $\theta_{lar}$ is the largest angular scale sampled in an observation with the GMRT, then $>80\%$ recovery of a source of size $0.3\times\theta_{lar}$ is possible. The upgraded GMRT (U-GMRT) providing 200 MHz instantaneous bandwidth between 300 - 500 MHz will allow a factor of two better recovery of a source of size $\theta_{lar}$ as compared to the GMRT at 300 MHz with 33 MHz bandwidth. We provide quantitative estimates for the improvement in extended source recovery in observations at low elevations and long durations. The presented simulations can be carried out for future radio telescopes such as the Square Kilometre Array (SKA) for optimisation of observing strategies to image extended radio sources.