System design and calibration of SITARA -- a global 21 cm short spacing interferometer prototype

Abstract

Global 21-cm experiments require exquisitely precise calibration of the measurement systems in order to separate the weak 21-cm signal from Galactic and extragalactic foregrounds as well as instrumental systematics. Hitherto, experiments aiming to make this measurement have concentrated on measuring this signal using the single element approach. However, an alternative approach based on interferometers with short baselines is expected to alleviate some of the difficulties associated with a single element approach such as precision modelling of the receiver noise spectrum. Short spacing Interferometer Telescope probing cosmic dAwn and epoch of ReionisAtion (SITARA) is a short spacing interferometer deployed at the Murchison Radio-astronomy Observatory (MRO). It is intended to be a prototype or a test-bed to gain a better understanding of interferometry at short baselines, and develop tools to perform observations and data calibration. In this paper, we provide a description of the SITARA system and its deployment at the MRO, and discuss strategies developed to calibrate SITARA. We touch upon certain systematics seen in SITARA data and their modelling. We find that SITARA has sensitivity to all sky signals as well as non-negligible noise coupling between the antennas. It is seen that the coupled receiver noise has a spectral shape that broadly matches the theoretical calculations reported in prior works. We also find that when appropriately modified antenna radiation patterns taking into account the effects of mutual coupling are used, the measured data are well modelled by the standard visibility equation.

arXiv comment27 pages, 17 figures, Accepted for publication in PASA

References in corpus (19)

• Astropy: A Community Python Package for Astronomy
• HEALPix -- a Framework for High Resolution Discretization, and Fast Analysis of Data Distributed on the Sphere
• An absorption profile centred at 78 megahertz in the sky-averaged spectrum
• A model of diffuse Galactic Radio Emission from 10 MHz to 100 GHz
• Revisiting the radio interferometer measurement equation. I. A full-sky Jones formalism
• The GMRT-EoR Experiment: A new upper limit on the neutral hydrogen power spectrum at z~8.6
• Constraining the unexplored period between reionization and the dark ages with observations of the global 21 cm signal
• First Intrinsic Anisotropy Observations with the Cosmic Background Imager
• First results on the Epoch of Reionization from First Light with SARAS 2
• Absolute calibration of a wideband antenna and spectrometer for sky noise spectral index measurements
• Spectral Index of the Diffuse Radio Background Between 50 and 100 MHz
• SARAS measurement of the Radio Background at long wavelengths
• SARAS 3 CD/EoR Radiometer: Design and Performance of the Receiver
• Measuring the Cosmological 21 cm Monopole with an Interferometer
• GMOSS: All-sky model of spectral radio brightness based on physical components and associated radiative processes
• On the detection of global 21-cm signal from Reionization using interferometers
• A survey of spatially and temporally resolved radio frequency interference in the FM band at the Murchison Radio-astronomy Observatory
• The statistics of low frequency radio interference at the Murchison Radio-astronomy Observatory
• A practical theorem on using interferometry to measure the global 21-cm signal