Understanding spectral artefacts in SKA-LOW 21-cm cosmology experiments: the impact of cable reflections

Abstract

The Cosmic Dawn was marked by the formation of the first stars, and preceded the Epoch of Reionization (EoR), when the Universe underwent a fundamental transformation caused by the radiation from these first stars and galaxies. Interferometric 21-cm experiments aim to probe redshifted neutral hydrogen signals from these periods, constraining the conditions of the early Universe. The SKA-Low instrument of the Square Kilometre Array (SKA) is envisaged to be the largest and most sensitive radio telescope at metre and centimetre wavelengths. The latest Aperture Array Verification Systems feature 7-m coaxial transmission lines connecting the low noise amplifiers to optical transmitters at the front of the analogue-receiving chain. An impedance mismatch between these components results in a partially reflected electromagnetic signal, introducing chromatic aberrations into the instrument bandpass. This causes power from the foreground signals to appear at higher delays, potentially contaminating the 'EoR window', a region in which the 21-cm signal should be detectable. We present an end-to-end simulation pipeline for SKA-Low using a composite sky model combining radio foregrounds from the Galactic and Extragalactic All-Sky MWA (GLEAM) Survey, Haslam $408$MHz, and a 1.5-cGpc 21-cm brightness temperature cube generated with the 21cmSPACE simulator. We derive a model for the scattering parameters of a coaxial transmission line in terms of its specifications and bulk material properties. Assuming identical cables of length $\le 15.0$m with impedance mismatch $\le 10\Omega$, the reflection is confined below the EoR window. However, we demonstrate that even a 0.1 per cent length tolerance introduces contamination with an absolute fractional difference of $\sim 10$ per cent across all accessible k-modes.

17 pages, 12 figures

References in corpus (15)

• Cosmology at Low Frequencies: The 21 cm Transition and the High-Redshift Universe
• GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey I: A low-frequency extragalactic catalogue
• The Epoch of Reionization Window: I. Mathematical Formalism
• Revisiting the radio interferometer measurement equation. I. A full-sky Jones formalism
• The Epoch of Reionization Window: II. Statistical Methods for Foreground Wedge Reduction
• First Season MWA EoR Power Spectrum Results at Redshift 7
• The Impact of the First Galaxies on Cosmic Dawn and Reionization
• Toward Empirical Constraints on the Global Redshifted 21 cm Brightness Temperature During the Epoch of Reionization
• The REACH radiometer for detecting the 21-cm hydrogen signal from redshift 7.5 to 28
• Mitigating Internal Instrument Coupling II: A Method Demonstration with the Hydrogen Epoch of Reionization Array
• Mapper of the IGM spin temperature: instrument overview
• The FHD/$\mathbf{\epsilon }$ppsilon Epoch of Reionization Power Spectrum Pipeline
• Impact of the Primordial Stellar Initial Mass Function on the 21-cm Signal
• Array Element Coupling in Radio Interferometry I: A Semi-Analytic Approach
• Signatures of Cosmic Ray Heating in 21-cm Observables

Cited by in corpus (2)

• Square Kilometre Array Science Data Challenge 3a: foreground removal for an EoR experiment
• The impact of lunar topography on the 21-cm power spectrum for grid-based arrays : Insights for the Dark-ages EXplorer (DEX)