Hertzog L. Bester
A5005661452- Radio Astronomy Observations and Technology
- Astrophysics and Cosmic Phenomena
- Galaxies: Formation, Evolution, Phenomena
- Soil Moisture and Remote Sensing
- Antenna Design and Optimization
- Cosmology and Gravitation Theories
- Pulsars and Gravitational Waves Research
- Astronomy and Astrophysical Research
- Gamma-ray bursts and supernovae
- Computational Physics and Python Applications
- Superconducting and THz Device Technology
- Astronomical Observations and Instrumentation
- Stellar, planetary, and galactic studies
- Seismic Waves and Analysis
- Scientific Computing and Data Management
- Radio Wave Propagation Studies
- Microwave Engineering and Waveguides
- GNSS positioning and interference
- Geophysics and Gravity Measurements
- Millimeter-Wave Propagation and Modeling
- Relativity and Gravitational Theory
- Structural Health Monitoring Techniques
- History and Developments in Astronomy
- Microwave and Dielectric Measurement Techniques
- Advanced Mathematical Theories and Applications
Rhodes University
2015-2025
South African Radio Astronomy Observatory
2019-2025
SKA Telescope, South Africa
2016-2018
The LOFAR Two-metre Sky Survey (LoTSS) is an ongoing sensitive, high-resolution 120-168MHz survey of the entire northern sky for which observations are now 20% complete. We present our first full-quality public data release. For this release 424 square degrees, or 2% eventual coverage, in region HETDEX Spring Field (right ascension 10h45m00s to 15h30m00s and declination 45$^\circ$00$'$00$''$ 57$^\circ$00$'$00$''$) were mapped using a fully automated direction-dependent calibration imaging...
In this data release from the LOFAR Two-metre Sky Survey (LoTSS) we present 120-168MHz images covering 27% of northern sky. Our coverage is split into two regions centred at approximately 12h45m +44$^\circ$30' and 1h00m +28$^\circ$00' spanning 4178 1457 square degrees respectively. The were derived 3,451hrs (7.6PB) High Band Antenna which corrected for direction-independent instrumental properties as well direction-dependent ionospheric distortions during extensive, but fully automated,...
The new generation of radio interferometers is characterized by high sensitivity, wide fields view and large fractional bandwidth. To synthesize the deepest images enabled dynamic range these instruments requires us to take into account direction-dependent Jones matrices, while estimating spectral properties sky in imaging deconvolution algorithms. In this paper we discuss implement a wide-band wide-field framework (DDFacet) based on image plane faceting, that takes generic effects....
The Low Frequency Array (LOFAR) is an ideal instrument to conduct deep extragalactic surveys. It has a large field of view and sensitive large-scale compact emission. is, however, very challenging synthesize thermal noise limited maps at full resolution, mainly because the complexity low-frequency sky direction dependent effects (phased array beams ionosphere). In this first paper series, we present new calibration imaging pipeline that aims producing high fidelity, dynamic range images with...
Abstract The inner ∼200 pc region of the Galaxy contains a 4 million M ⊙ supermassive black hole (SMBH), significant quantities molecular gas, and star formation cosmic-ray energy densities that are roughly two orders magnitude higher than corresponding levels in Galactic disk. At distance only 8.2 kpc, presents astronomers with unique opportunity to study diverse range energetic astrophysical phenomena, from stellar objects extreme environments, SMBH star-formation-driven feedback processes...
We present the confusion-limited 1.28 GHz MeerKAT DEEP2 image covering one $\approx 68'$ FWHM primary beam area with $7.6''$ resolution and $0.55 \pm 0.01$ $\mu$Jy/beam rms noise. Its J2000 center position $\alpha=04^h 13^m 26.4^s$, $\delta=-80^\circ 00' 00''$ was selected to minimize artifacts caused by bright sources. introduce new 64-element array describe commissioning observations measure attenuation pattern, estimate telescope pointing errors, pinpoint $(u,v)$ coordinate errors offsets...
ABSTRACT MIGHTEE is a galaxy evolution survey using simultaneous radio continuum, spectropolarimetry, and spectral line observations from the South African MeerKAT telescope. When complete, will image ∼20 deg2 over COSMOS, E-CDFS, ELAIS-S1, XMM-Newton Large Scale Structure field (XMM-LSS) extragalactic deep fields with central frequency of 1284 MHz. These were selected based on extensive multiwavelength data sets numerous existing forthcoming observational campaigns. Here, we describe...
ABSTRACT We present the SARAO MeerKAT Galactic Plane Survey (SMGPS), a 1.3 GHz continuum survey of almost half (251° ≤l ≤ 358° and 2° 61° at |b| $1{_{.}^{\circ}}5$). SMGPS is largest, most sensitive, highest angular resolution 1 plane yet carried out, with an 8 arcsec broad-band root-mean-square sensitivity ∼10–20 μJy beam−1. Here, we describe first publicly available data release from which comprises cubes frequency-resolved images over 908–1656 MHz, power-law fits to images, zeroth moment...
We present MeerKAT 1.28 GHz total-intensity, polarization, and spectral-index images covering the giant (projected length $l \approx 1.57$~Mpc) X-shaped radio source PKS~2014$-$55 with an unprecedented combination of brightness sensitivity angular resolution. They show clear "double boomerang" morphology hydrodynamical backflows from straight main jets deflected by large oblique hot-gas halo host galaxy PGC~064440. The magnetic field orientation in follows flow lines through secondary wings....
The Shapley Supercluster ($\langle z \rangle\approx0.048$) contains several tens of gravitationally bound clusters and groups, making it is an ideal subject for radio studies cluster mergers. We used new high sensitivity observations to investigate the less energetic events mass assembly in from supercluster down galactic scales. created total intensity images full region between A 3558 3562, $\sim 230$ 1650$ MHz, using ASKAP, MeerKAT GMRT, with sensitivities ranging 6$ 100$ $\mu$Jy...
ABSTRACT We report on a radiopolarimetric observation of the Saturn–Jupiter Great Conjunction 2020 using MeerKAT L-band system, initially carried out for science verification purposes, which yielded serendipitous discovery pulsar. The radiation belts Jupiter are very bright and time variable: coupled with sensitivity MeerKAT, this necessitated development dynamic imaging techniques, reported in work. present deep radio ‘movie’ revealing Jupiter’s rotating magnetosphere, detection Callisto,...
Medium-timescale (minutes to hours) radio transients are a relatively unexplored population. The wide field-of-view and high instantaneous sensitivity of instruments such as MeerKAT provides an opportunity probe this class sources, using image-plane detection techniques. We aim systematically mine archival synthesis imaging data in order search for medium-timescale variables that not detected by conventional long-track image deploy prototype blind transient variable pipeline named TRON. This...
Medium-timescale (minutes to hours) radio transients are a relatively unexplored population. The wide field-of-view and high instantaneous sensitivity of instruments such as MeerKAT provides an opportunity probe this class sources, using image-plane detection techniques. previous letter in series describes our project associated TRON pipeline designed mine archival data for transient variable sources. In letter, we report on new transient, flare, with Gaia DR3 6865945581361480448, G type...
Abstract Medium-timescale (minutes to hours) radio transients are a relatively unexplored population. The wide field-of-view and high instantaneous sensitivity of instruments such as MeerKAT provides an opportunity probe this class sources, using image-plane detection techniques. We aim systematically mine archival synthesis imaging data in order search for medium-timescale variables that not detected by conventional long-track image deploy prototype blind transient variable pipeline named...
Abstract Medium-timescale (minutes to hours) radio transients are a relatively unexplored population. The wide field-of-view and high instantaneous sensitivity of instruments such as MeerKAT provides an opportunity probe this class sources, using image-plane detection techniques. previous letter in series describes our project associated TRON pipeline designed mine archival data for transient variable sources. In letter, we report on new transient, flare, with Gaia DR3 6865945581361480448, G...
The construction of the seven-dish Karoo Array Telescope (KAT-7) array in region Northern Cape South Africa was intended primarily as an engineering prototype for technologies and techniques applicable to MeerKAT telescope. This paper looks at main scientific highlights from this effort, discusses their applicability both other next-generation radio telescopes. In particular, we found that composite dish surface works well, but it becomes complicated fabricate a lacking circular symmetry;...
CLEAN, the commonly employed imaging algorithm in radio interferometry, suffers from a number of shortcomings: its basic version it does not have concept diffuse flux, and common practice convolving CLEAN components with beam erases potential for super-resolution; output uncertainty information; produces images unphysical negative flux regions; results are highly dependent on so-called weighting scheme as well any human choice masks to guiding imaging. Here, we present Bayesian resolve which...
ABSTRACT Precision antenna calibration is required for mitigating the impact of foreground contamination in 21 cm cosmological radio surveys. One widely studied source error effect missing point sources sky model; however, poorly understood diffuse galactic emission also creates a bias that can complicate clean separation foregrounds from signal. In this work, we present technique suppressing with temporal filtering interferometric visibilities observed drift-scan mode. We demonstrate on...
The 21 cm transition from neutral Hydrogen promises to be the best observational probe of Epoch Reionisation (EoR). This has led construction low-frequency radio interferometric arrays, such as Reionization Array (HERA), aimed at systematically mapping this emission for first time. Precision calibration, however, is a requirement in observations. Due spatial compactness HERA, array prone effects mutual coupling, which inevitably lead non-smooth calibration errors that contaminate data. When...
Stimela2 is a new-generation framework for developing data reduction workflows. It designed radio astronomy but can be adapted other processing applications. aims at the middle ground between ease of development, human readability, and enabling robust, scalable reproducible represents workflows by linear, concise intuitive YAML-format "recipes". Atomic tasks (binary executables, Python functions code, CASA tasks) are described "cab definitions" detailing each task's "schema" (inputs...
Abstract Radio interferometric gain calibration can be biased by incomplete sky models and radio frequency interference, resulting in artefacts that restrict the dynamic range of images. It has been suggested algorithms employing heavy-tailed likelihood functions are less susceptible to this due their robustness against outliers data. We present an algorithm based on a Student’s t-distribution which leverages framework complex optimisation Wirtinger calculus for efficient robust calibration....