Abstract:
This work investigates a particular class of artefacts, or ghost sources, in radio in-
terferometric images. Earlier observations with (and simulations of) the Westerbork
Synthesis Radio Telescope (WSRT) suggested that these were due to calibration with
incomplete sky models. A theoretical framework is derived that validates this sug-
gestion, and provides predictions of ghost formation in a two-source scenario. The
predictions are found to accurately match the result of simulations, and qualitatively
reproduce the ghosts previously seen in observational data. The theory also provides
explanations for many previously puzzling features of these artefacts (regular geom-
etry, PSF-like sidelobes, seeming independence on model
ux), and shows that the
observed phenomenon of
ux suppression a ecting unmodelled sources is due to the
same mechanism. We demonstrate that this ghost formation mechanism is a funda-
mental feature of calibration, and exhibits a particularly strong and localized signature
due to array redundancy. To some extent this mechanism will a ect all observations
(including those with non-redundant arrays), though in most cases the ghosts remain
hidden below the noise or masked by other instrumental artefacts. The implications
of such errors on future deep observations are discussed.
