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Register a new userThe BINGO Project II: Instrument Description
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The measurement of the diffuse $21$-cm radiation from the hyperfine transition of neutral hydrogen (HI signal) in different redshifts is an important tool for modern cosmology. However, detecting this faint signal with non-cryogenic receivers in single-dish telescopes is a challenging task. The BINGO (Baryon Acoustic Oscillations from Integrated Neutral Gas Observations) radio telescope is an instrument designed to detect baryonic acoustic oscillations (BAO) in the cosmological HI signal, in the redshift interval $0.127 le z le 0.449$. This paper describes the BINGO radio telescope, including the current status of the optics, receiver, observational strategy, calibration and the site. BINGO has been carefully designed to minimize systematics, being a transit instrument with no moving dishes and 28 horns operating in the frequency range $980 le u le 1260$ MHz. Comprehensive laboratory tests were conducted for many of the BINGO subsystems and the prototypes of the receiver chain, horn, polarizer, magic tees and transitions have been successfully tested between 2018-2020. The survey was designed to cover $sim 13%$ of the sky, with the primary mirror pointing at declination $delta=-15^{circ}$. The telescope will see an instantaneous declination strip of $14.75^{circ}$. The results of the prototype tests closely meet those obtained during the modelling process, suggesting BINGO will perform according to our expectations. After one year of observations with a 60% duty cycle, BINGO should achieve an expected sensitivity of $102 mu K$ for 28 horns and 30 redshift bins, considering one polarization and be able to measure the HI power spectrum in a competitive time frame.
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BINGO is a unique radio telescope designed to make the first detection of Baryon Acoustic Oscillations (BAO) at radio frequencies. This will be achieved by measuring the distribution of neutral hydrogen gas at cosmological distances using a technique called Intensity Mapping. Along with the Cosmic Microwave Background anisotropies, the scale of BAO is one of the most powerful probes of cosmological parameters, including dark energy. The telescope will be built in a very low RFI site in South America and will operate in the frequency range from 0.96 GHz to 1.26 GHz. The telescope design consists of two $thicksim$ 40-m compact mirrors with no moving parts. Such a design will give the excellent polarization performance and very low sidelobe levels required for intensity mapping. With a feedhorn array of 50 receivers, it will map a $15^{circ}$ declination strip as the sky drifts past the field-of-view of the telescope. The BINGO consortium is composed Universidade de S~ao Paulo, Instituto Nacional de Pesquisas Espaciais (Brazil), University of Manchester and University College London (United Kingdom), ETH Zurich (Switzerland) and Universidad de La Republica (Uruguay). The telescope assembly and horn design and fabrication are under way in Brazil. The receiver was designed in UK and will be developed in Brazil, with most of the components for the receiver will also be supplied by Brazilian industry. The experience and science goals achieved by the BINGO team will be advantageous as a pathfinder mission for the Square Kilometre Array (SKA) project. This paper reports the current status of the BINGO mission, as well as preliminary results already obtained for the instrumentation development.
The BINGO telescope was designed to measure the fluctuations of the 21-cm radiation arising from the hyperfine transition of neutral hydrogen and aims to measure the Baryon Acoustic Oscillations (BAO) from such fluctuations, therefore serving as a pathfinder to future deeper intensity mapping surveys. The requirements for the Phase 1 of the projects consider a large reflector system (two 40 m-class dishes in a crossed-Dragone configuration), illuminating a focal plane with 28 horns to measure the sky with two circular polarisations in a drift scan mode to produce measurements of the radiation in intensity as well as the circular polarisation. In this paper we present the optical design for the instrument. We describe the intensity and polarisation properties of the beams and the optical arrangement of the horns in the focal plane to produce a homogeneous and well-sampled map after the end of Phase 1. Our analysis provides an optimal model for the location of the horns in the focal plane, producing a homogeneous and Nyquist sampled map after the nominal survey time. We arrive at an optimal configuration for the optical system, including the focal plane positioning and the beam behavior of the instrument. We present an estimate of the expected side lobes both for intensity and polarisation, as well as the effect of band averaging on the final side lobes. The cross polarisation leakage values for the final configuration allow us to conclude that the optical arrangement meets the requirements of the project. We conclude that the chosen optical design meets the requirements for the project in terms of polarisation purity, area coverage as well as homogeneity of coverage so that BINGO can perform a successful BAO experiment. We further conclude that the requirements on the placement and r.m.s. error on the mirrors are also achievable so that a successful experiment can be conducted.(Abridged)
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