Simulations of ionospheric refraction on radio interferometric data
  The Epoch of Reionisation (EoR) is the period within which the neutral
universe transitioned to an ionised one. This period remains unobserved using
low-frequency radio interferometers which target the 21 cm signal of neutral
hydrogen emitted in this era. The Murchison Widefield Array (MWA) radio
telescope was built with the detection of this signal as one of its major
science goals. One of the most significant challenges towards a successful
detection is that of calibration, especially in the presence of the Earth's
ionosphere. By introducing refractive source shifts, distorting source shapes
and scintillating flux densities, the ionosphere is a major nuisance in
low-frequency radio astronomy. We introduce SIVIO, a software tool developed
for simulating observations of the MWA through different ionospheric conditions
estimated using thin screen approximation models and propagated into the
visibilities. This enables us to directly assess the impact of the ionosphere
on observed EoR data and the resulting power spectra. We show that the
simulated data captures the dispersive behaviour of ionospheric effects. We
show that the spatial structure of the simulated ionospheric media is
accurately reconstructed either from the resultant source positional offsets or
from parameters evaluated during the data calibration procedure. In turn, this
will inform on the best strategies of identifying and efficiently eliminating
ionospheric contamination in EoR data moving into the Square Kilometre Array
era.
