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, which is 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.

中文翻译：

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电离层折射对无线电干涉数据的模拟

再电离时代（EoR）是中性宇宙转变为电离宇宙的时期。使用低频无线电干涉仪仍无法观测到这一时期，该干涉仪瞄准了这一时期发射的 21 厘米中性氢信号。默奇森宽场阵列 (MWA) 射电望远镜的建造将检测该信号作为其主要科学目标之一。成功探测的最大挑战之一是校准，尤其是在存在地球电离层的情况下。通过引入折射源偏移、扭曲源形状和闪烁通量密度，电离层是低频射电天文学中的主要麻烦。我们介绍西维奥，一种软件工具，用于模拟通过不同电离层条件对 MWA 的观测，使用薄屏幕近似模型进行估计并传播到能见度中。这使我们能够直接评估电离层对观测到的 EoR 数据和由此产生的功率谱的影响。我们表明，模拟数据捕获了电离层效应的分散行为。我们表明，模拟电离层介质的空间结构可以根据产生的源位置偏移量或数据校准过程中评估的参数准确地重建。反过来，这将为进入平方公里阵列时代的 EoR 数据中识别和有效消除电离层污染的最佳策略提供信息。