Chuneeta D. Nunhokee
A5073920410- Radio Astronomy Observations and Technology
- Astrophysics and Cosmic Phenomena
- Antenna Design and Optimization
- Particle Accelerators and Free-Electron Lasers
- Radio Wave Propagation Studies
- Galaxies: Formation, Evolution, Phenomena
- Superconducting Materials and Applications
- Astronomy and Astrophysical Research
- Gamma-ray bursts and supernovae
- Soil Moisture and Remote Sensing
- Electromagnetic Compatibility and Measurements
- Scientific Research and Discoveries
- Pulsed Power Technology Applications
- Superconducting and THz Device Technology
- Advanced Wireless Communication Techniques
- Gyrotron and Vacuum Electronics Research
- Millimeter-Wave Propagation and Modeling
- Sparse and Compressive Sensing Techniques
- Advanced MRI Techniques and Applications
- Cosmology and Gravitation Theories
- Computational Physics and Python Applications
- Microwave Engineering and Waveguides
- Pulsars and Gravitational Waves Research
- Stellar, planetary, and galactic studies
- Radio Frequency Integrated Circuit Design
International Centre for Radio Astronomy Research
2023-2025
Curtin University
2023-2025
ARC Centre of Excellence for All-sky Astrophysics
2023-2025
ASTRO-3D
2023-2025
University of California, Berkeley
2018-2023
Rhodes University
2014-2020
University of Pennsylvania
2019-2020
Abstract We report upper limits on the Epoch of Reionization 21 cm power spectrum at redshifts 7.9 and 10.4 with 18 nights data (∼36 hr integration) from Phase I Hydrogen Array (HERA). The show evidence for systematics that can be largely suppressed systematic models down to a dynamic range ∼10 9 respect peak foreground power. This yields 95% confidence limit <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi...
Abstract Recently, the Hydrogen Epoch of Reionization Array (HERA) has produced experiment’s first upper limits on power spectrum 21 cm fluctuations at z ∼ 8 and 10. Here, we use several independent theoretical models to infer constraints intergalactic medium (IGM) galaxies during epoch reionization from these limits. We find that IGM must have been heated above adiabatic-cooling threshold by 8, uncertainties about ionization radio background. Combining HERA with complementary observations...
Abstract We report the most sensitive upper limits to date on 21 cm epoch of reionization power spectrum using 94 nights observing with Phase I Hydrogen Epoch Reionization Array (HERA). Using similar analysis techniques as in previously reported limits, we find at 95% confidence that Δ 2 ( k = 0.34 h Mpc −1 ) ≤ 457 mK z 7.9 and 0.36 3496 10.4, an improvement by a factor 2.1 2.6, respectively. These are mostly consistent thermal noise over wide range after our data quality cuts, despite...
We introduce Probing Radio Intensity at high-Z from Marion (PRI Z M), a new experiment designed to measure the globally averaged sky brightness, including expected redshifted 21[Formula: see text]cm neutral hydrogen absorption feature arising formation of first stars. PRI M consists two dual-polarization antennas operating central frequencies 70 and 100[Formula: text]MHz, is located on Island in sub-Antarctic. describe initial design configuration instrument that was installed 2017, we...
Abstract This paper presents the design and deployment of Hydrogen Epoch Reionization Array (HERA) phase II system. HERA is designed as a staged experiment targeting 21 cm emission measurements Reionization. First results from I array are published early 2022, system nearing completion. We describe discuss progress on commissioning future upgrades. As designated Square Kilometre pathfinder instrument, we also show number “case studies” that investigate systematics seen while system, which...
Abstract The Epoch of Reionization (EoR) is an uncharted era in our universe’s history during which the birth first stars and galaxies led to ionization neutral hydrogen intergalactic medium. There are many experiments investigating EoR by tracing 21 cm line hydrogen. Because this signal very faint difficult isolate, it crucial develop analysis techniques that maximize sensitivity suppress contaminants data. It also imperative understand trade-offs between different methods their effects on...
Abstract We present limits on the 21 cm power spectrum from Epoch of Reionization using data 64 antenna configuration Donald C. Backer Precision Array for Probing (PAPER) analyzed through a pipeline independent previous PAPER analyses. Previously reported results have been found to contain significant signal loss. Several lossy steps pipelines not included in this analysis, namely delay-based foreground filtering, optimal fringe-rate and empirical covariance-based estimators. Steps that...
This work investigates a particular class of artefacts, or ghost sources, in radio interferometric images. Earlier observations with (and simulations ) the Westerbork Synthesis Radio Telescope suggested that these were due to calibration incomplete sky models. A theoretical framework is derived validates this suggestion, and provides predictions formation two-source scenario. The are found accurately match result simulations, qualitatively reproduce ghosts previously seen observational data....
ABSTRACT In 21-cm cosmology, precision calibration is key to the separation of neutral hydrogen signal from very bright but spectrally smooth astrophysical foregrounds. The Hydrogen Epoch Reionization Array (HERA), an interferometer specialized for cosmology and now under construction in South Africa, was designed be largely calibrated using self-consistency repeated measurements same interferometric modes. This technique, known as redundant-baseline resolves most internal degrees freedom...
Abstract We discuss absolute calibration strategies for Phase I of the Hydrogen Epoch Reionization Array (HERA), which aims to measure cosmological 21 cm signal from Reionization. HERA is a drift-scan array with 10° wide field view, meaning bright, well-characterized point-source transits are scarce. This, combined HERA’s redundant sampling uv plane and modest angular resolution instrument, make traditional sky-based self-calibration techniques difficult implement high dynamic range....
21 cm cosmology is a promising new probe of the evolution visible matter in our universe, especially during poorly-constrained Cosmic Dawn and Epoch Reionization. However, order to separate signal from bright astrophysical foregrounds, we need an exquisite understanding telescopes so as avoid adding spectral structure spectrally-smooth foregrounds. One powerful calibration method relies on repeated simultaneous measurements same interferometric baseline solve for sky instrumental parameters...
Current-generation low frequency interferometers constructed with the objective of detecting high-redshift 21 cm background, aim to generate power spectra brightness-temperature contrast neutral hydrogen in primordial intergalactic medium. Two-dimensional (power Fourier modes parallel and perpendicular line sight) formed from interferometric visibilities have been shown delineate a boundary between spectrally-smooth foregrounds (known as wedge) spectrally-structured background emission (the...
We introduce DAYENU, a linear, spectral filter for HI intensity mapping that achieves the desirable foreground mitigation and error minimization properties of inverse co-variance weighting with minimal modeling underlying data. Beyond 21 cm power-spectrum estimation, our is suitable any analysis where high dynamic-range removal spectrally smooth foregrounds in irregularly (or regularly) sampled data required, something required by many other techniques. Our filtering matrix diagonalized...
The key challenge in the observation of redshifted 21-cm signal from cosmic reionization is its separation much brighter foreground emission. Such relies on different spectral properties two components, although, real life, intrinsic spectrum often corrupted by instrumental response, inducing systematic effects that can further jeopardize measurement signal. In this paper, we use Gaussian Process Regression to model both emission and systematics $\sim 2$ hours data Hydrogen Epoch...
ABSTRACT Detection of the faint 21 cm line emission from Cosmic Dawn and Epoch Reionization will require not only exquisite control over instrumental calibration systematics to achieve necessary dynamic range observations but also validation analysis techniques demonstrate their statistical properties signal loss characteristics. A key ingredient in achieving this is ability perform high-fidelity simulations kinds data that are produced by large, many-element, radio interferometric arrays...
Foreground power dominates the measurements of interferometers that seek a statistical detection highly-redshifted HI emission from Epoch Reionization (EoR). The chromaticity instrument creates boundary in Fourier transform frequency (proportional to $k_\parallel$) between spectrally smooth emission, characteristic strong synchrotron foreground (the "wedge"), and structured EoR "EoR window"). Faraday rotation can inject spectral structure into otherwise polarized which through effects or...
Precise measurements of the 21 cm power spectrum are crucial for understanding physical processes hydrogen reionization. Currently, this probe is being pursued by low-frequency radio interferometer arrays. As these experiments come closer to making a first detection signal, error estimation will play an increasingly important role in setting robust measurements. Using delay approach, we have produced critical examination different ways that one can estimate bars on spectrum. We do through...
Abstract A critical challenge in the observation of redshifted 21 cm line is its separation from bright Galactic and extragalactic foregrounds. In particular, instrumental leakage polarized foregrounds, which undergo significant Faraday rotation as they propagate through interstellar medium, may harmfully contaminate power spectrum. We develop a formalism to describe due widefield effects visibility-based spectra measured with redundant arrays, extending delay-spectrum approach presented...
We report the most sensitive upper limits to date on 21 cm epoch of reionization power spectrum using 94 nights observing with Phase I Hydrogen Epoch Reionization Array (HERA). Using similar analysis techniques as in previously reported (HERA Collaboration 2022a), we find at 95% confidence that $\Delta^2(k = 0.34$ $h$ Mpc$^{-1}$) $\leq 457$ mK$^2$ $z 7.9$ and $\Delta^2 (k 0.36$ Mpc$^{-1}) \leq 3,496$ 10.4$, an improvement by a factor 2.1 2.6 respectively. These are mostly consistent thermal...
This paper presents the design and deployment of Hydrogen Epoch Reionization Array (HERA) phase II system. HERA is designed as a staged experiment targeting 21 cm emission measurements Reionization. First results from I array are published early 2022, system nearing completion. We describe discuss progress on commissioning future upgrades. As designated Square Kilometer (SKA) pathfinder instrument, we also show number "case studies" that investigate systematics seen while system, which may...
Radio interferometers targeting the 21cm brightness temperature fluctuations at high redshift are subject to systematic effects that operate over a range of different timescales. These can be isolated by designing appropriate Fourier filters in fringe-rate (FR) space, pair local sidereal time (LST). Applications FR filtering include separating correlated with rotating sky vs. those relative ground, down-weighting emission primary beam sidelobes, and suppressing noise. causes noise...
ABSTRACT Radio interferometers targeting the 21cm brightness temperature fluctuations at high redshift are subject to systematic effects that operate over a range of different time-scales. These can be isolated by designing appropriate Fourier filters in fringe-rate (FR) space, pair local sidereal time. Applications FR filtering include separating correlated with rotating sky versus those relative ground, down-weighting emission primary beam sidelobes, and suppressing noise. causes noise...
Abstract Observations of the 21 cm signal face significant challenges due to bright astrophysical foregrounds that are several orders magnitude higher than brightness hydrogen line, along with various systematics. Successful experiments require accurate calibration and foreground mitigation. Errors introduced during process such as systematics can disrupt intrinsic frequency smoothness foregrounds, leading power leakage into Epoch Reionisation window. Therefore, it is essential develop...
We introduce Probing Radio Intensity at high-Z from Marion (PRIZM), a new experiment designed to measure the globally averaged sky brightness, including expected redshifted 21 cm neutral hydrogen absorption feature arising formation of first stars. PRIZM consists two dual-polarization antennas operating central frequencies 70 and 100 MHz, is located on Island in sub-Antarctic. describe initial design configuration instrument that was installed 2017, we present preliminary data demonstrate...