Conveners
Astrophysics & Space Science: Space Science Session 1
- Ruhann Steyn (Centre for Space Research, North-West University)
Astrophysics & Space Science: Cosmology
- Matt Hilton (University of the Witwatersrand)
Astrophysics & Space Science: Space Science Session 2
- Moumita Aich (University of Witwatersrand)
Astrophysics & Space Science: Radio astronomy
- Geoff Beck (University of the Witwatersrand)
Astrophysics & Space Science: Galaxy clusters
- Sthabile Kolwa (UNISA)
Astrophysics & Space Science: Space Science Session 3
- Ruhann Steyn (Centre for Space Research, North-West University)
Astrophysics & Space Science: Astrophysics
- Christo Venter (Centre for Space Research)
Astrophysics & Space Science: Space Science Session 4
- Zama Katamzi-Joseph
Astrophysics & Space Science: Dark matter and instrumentation
- Andrew Chen (University of the Witwatersrand)
Astrophysics & Space Science: Division Meeting
- Geoff Beck (University of the Witwatersrand)
Astrophysics & Space Science: Miscellaneous astrophysics
- Nceba Mhlahlo (University of the Witwatersrand)
Astrophysics & Space Science: Astrophysics and Space Science - Space Science Session 5
- Joseph Omojola (North-West University)
Astrophysics & Space Science: Astrophysics and Space Science - Space Science Session 6
- Joseph Omojola (North-West University)
Astrophysics & Space Science: High energy astrophysics
- Geoff Beck (University of the Witwatersrand)
The climate crisis persists, as the global community has yet to fully embrace the actions needed to tackle it. The decade from 2010 to 2019 was the hottest on record, leading to devastating wildfires, hurricanes, droughts, floods, and other climate-related disasters worldwide. To limit global warming to 1.5ยฐC above pre-industrial levels, emissions must already be on the decline and need to be...
This study reports on nighttime medium-scale traveling ionospheric disturbances (MSTIDs) observed by conjugate midlatitude all-sky imagers in Sutherland (32.4โฆS, 20.8โฆE; magnetic latitude: โผ-40.9โฆ) and Asiago (45.87โฆN, 11.53โฆE; magnetic latitude: โผ40.3โฆ) on the 4th of October 2018. These MSTIDs had fronts elongated along the northeast-southwest (NE-SW) and northwest-southeast (NW-SE)...
Monitoring atmospheric conditions is crucial for understanding the behaviour of aerosols, which directly impact air quality, climate, and satellite-based remote sensing applications. In this study, we focus on the atmospheric boundary layer (ABL), which regulates the dispersion, transport, and transformation of aerosols. Ceilometers, which measure the height of the boundary layer by detecting...
In this work, we study the dynamics of the universe using Thawing Dark Energy (TDE) model with a minimally coupled scalar field that evolves away from the dominance of potential energy. As the equation of state parameter ๐ค(๐) evolves, this offers a dynamic framework where the impact of dark energy may change over time. The structure formation of the universe will be highlighted in TDE using...
Various empirical correlations between observable and derived parameters have been proposed to use Gamma-Ray Bursts (GRBs) as standard candles similar to Type Ia supernovae (SNe Ia) for measuring cosmological distances. The Yonetoku relation, which connects the intrinsic peak energy to the isotropic peak luminosity, stands out as a promising tool. In this work, we present results from machine...
The observation of galactic cosmic ray (GCR) deuteron at the Earth has been done precisely with the PAMELA and AMS02 space detectors and reported from July 2006 to September 2014 and from May 2011 to April 2021, respectively. These observations span time frames that include solar maximum and both minimum modulation conditions in the A > 0 and A < 0 magnetic field cycles at rigidities between ~...
The latest DESI results, suggesting a dynamical dark energy equation of state, have reinvigorated interest in modified teleparallel theories, such as $f(T)$ gravity, as viable alternatives to the standard cosmological model. In this talk, I present a systematic investigation of several popular and novel $f(T)$ models, examining their viability in light of current observational data. By...
Neutral hydrogen (HI) intensity mapping (IM) experiments
probe the large-scale structure of the universe through the integrated
redshifted 21-cm line emission from unresolved sources of neutral
hydrogen. Optical surveys also probe the large-scale structure of the
universe with much higher precision and depth by mapping the galaxy
distribution. In this article, we study the...
The topside ionosphere is highly sensitive to solar flare activity, which leads to sudden enhancements in solar X-ray and EUV flux. These enhancements can significantly alter electron density profiles, impacting satellite communication and navigation systems. This study examines the response of topside electron density (Ne) to solar flares using in-situ data from the Swarm satellites. Electron...
The ionosphere is a dynamic, inhomogeneous and conductive plasma formed from the interaction of solar Extreme Ultraviolet (EUV) and X-ray radiation with the quasi-neutral atmosphere of the Earth, found at 60 โ 1000 km above sea level. With different peak levels of ionization, it is predominantly studied by determining the total number of particles that pass through a square meter area between...
The diurnal variation of plasma density in the ionosphere is largely characterized by a single peak around local noon. However, diurnal double maxima (DDM) is sometimes observed when two distinct peaks and one valley in plasma density appear during the local daytime. Understanding DDM structures is essential for studying ionospheric dynamics and their key drivers, including neutral winds, **E...
Pinpointing the true source of radio emission in galaxies is a rather complex task that requires detailed modelling of radio spectral energy distributions. With the recent availability of catalogues of radio sources detected with interferometers such as MeerKAT, uGMRT, and LOFAR, we are able to push down the detectable flux range to the point where we can detect the faintest radio emission in...
Fast Radio Bursts (FRBs) are millisecond-duration radio emissions originating from cosmological distances, as indicated by their large dispersion measures. While numerous FRBs have now been localised to their host galaxies, a distinct class of compact electromagnetic counterpart, the Persistent Radio Source (PRS), has also been identified in some cases. These PRSs, have so far only been found...
Transient surveys play a crucial role in understanding the dynamic Universe, with radio transients serving as indicators of explosive and energetic astrophysical events. Despite their importance, conducting commensal radio imaging surveys for transients often demands extensive computational resources, data storage, and processing time. The MeerKAT radio telescope, with its high sensitivity and...
Giant radio galaxies (GRGs) are peculiar astrophysical objects because of their exceptionally large linear sizes (>0.7 Mpc). The cause for their huge sizes remains a mystery.
We investigate the spectral behaviour of a small sample of seven (7) GRGs detected from the MeerKAT Galaxy Cluster Legacy Survey (MGCLS). These sources have a minimum linear size of 0.723 Mpc to a maximum linear size of...
Galaxies are gravitationally bound systems composed of stars, gas, dust, and dark matter. Various galaxy propertiesโsuch as luminosity, stellar mass, and star formation rateโare significantly correlated with their local environment, such as whether they reside in dense clusters or more isolated regions. Understanding these environmental correlations is crucial for studying galaxy evolution...
We present an analysis of the X-ray bright galaxy cluster ZwCl 3146 (redshift z = 0.291) using archival 90 ks Chandra observations, along with our 1.4 GHz GMRT observations. Beta model subtracted residual and unsharp X-ray images reveal spiral-like features within the central 230 kpc, indicative of gas sloshing in the intracluster medium (ICM). We also detect an offset of about 11 kpc between...
The Atacama Cosmology Telescope (ACT) conducted an arcmin resolution survey of the southern sky at millimetre wavelengths from 2008-2022. In this talk I will present an update on the ACT search for galaxy clusters using the redshift independent Sunyaev-Zel'dovich (SZ) effect, using data from the full ACT survey, covering 15,000 square degrees. The final ACT Data Release 6 (DR6) cluster catalog...
The Earthโs magnetic field plays a critical role in shielding our planet from solar and cosmic radiation, yet the South Atlantic Anomaly (SAA) region represents a significant weakening of this protective shield. This research aims to model the temporal and spatial evolution of the SAA region using the Revised Spherical Cap Harmonic Analysis (R-SCHA) technique, providing improved regional...
Variations in thermospheric density play an essential role in satellite operations, particularly during geomagnetic disturbances, where fluctuations in atmospheric drag impact orbital stability. A significant incident on February 4, 2022, saw SpaceX lose 38 Starlink satellites due to unanticipated atmospheric drag following a geomagnetic storm. This study aims to identify high- risk periods in...
This talk will present results of ionospheric changes during the 23-25 March 2023 geomagnetic storm using observational and modeling data over the African-European sector. Both ionosonde and Swarm observational results show that mid latitudes experienced negative storm effects which have been attributed to thermospheric composition changes. We use models to simulate the ionospheric behavior...
This study investigated the impact of solar proton events (SPE) on the upper atmosphere over
South Africa during intense geomagnetic storms in May (Dst = -412 nT) and October 2024 (Dst
= -333 nT). Utilizing the NRLMSISE-2.0 atmospheric model and SOHO data, we characterized
storm-time atmospheric composition and energetic particle fluxes. Significant fluctuations in atmospheric
constituents...
This study presents a statistical analysis of the occurrence rate of midlatitude nighttime medium scale traveling ionospheric disturbances (MSTIDs) that were detected in Swarm plasma density measurements from 2014 to 2023. Monthly and local time variations of MSTID occurrence rates are compared in four longitude sectors: America, Africa, Asia, and Pacific. The spatial distribution showed a...
Blazars, a subclass of active galactic nuclei, have emerged as candidates for the sources of very-high-energy astrophysical neutrinos observed by the IceCube Neutrino Observatory. Notable temporal and spatial coincidences, particularly the event IceCube-170922A coinciding with a flare from TXS 0506+056, have sparked interest in the connection between these objects and neutrino production. In...
Recently the KM3NeT neutrino telescope detected the most-energetic neutrino event ever, dubbed KM3-230213A, at an estimated energy of 220 PeV. Given its near horizontal direction and exceptionally high energy, the most likely explanation is that the muon resulted from interaction of a muon neutrino of cosmic origin. In this talk I will explore an astrophysical source origin, both transients...
Dark Matter (DM) makes up a significant portion of the universe's mass-energy content, yet its fundamental nature remains elusive. Neutrinos are nearly massless particles that interact weakly with ordinary matter and may provide evidence of subtle interactions with DM. One possibility is that dense DM spikes, which form around supermassive black holes, can weaken the high-energy neutrino flux...
The solar photospheric differential rotation rate has novel implications to the structure of the heliospheric magnetic field. The period of the solar poles is ~ 35 days, and ~ 25 days at the equator. In this study, the Doppler shift (either blue or red) of 116 Dopplergrams from the Helioseismic and Magnetic Imager instrument on board the Solar Dynamics Observatory are investigated to...
In this study, the previously established set of modulation parameters used to reproduce PAMELA and AMS-02 proton observations between 2006 and 2022 is applied in the 3D steady-state drift numerical model to simulate antiproton spectra observed by AMS-02 detector between 2011 and 2021. In this way, the only differences between galactic protons and antiprotons simulations in the model remain...
In order to reliably estimate cosmic ray (CR) transport effects due to turbulence in the heliospheric magnetic field (HMF), and to validate existing diffusion theories (see, e.g., Engelbrecht et al., 2022, for a review), direct simulations, which involve solving the Newton-Lorentz equation numerically, may be employed (e.g., Els and Engelbrecht, 2024). Prior work, guided by turbulence...
With the WIMP parameter space slowly being ruled out by experiments on all fronts, axions have become a highly studied alternative dark matter candidate. In this talk we present a particle physics model where the pion states of a dark copy of QCD have both axion and dilaton phenomenologies. This model allows for the formation of dilute axion stars over a far larger parameter space than allowed...
MeerKAT's combination of high-sensitivity and angular resolution makes it a particularly well suited radio interferometer for detecting faint cosmic radio emissions that would otherwise remain inaccessible by other instruments.
This capability is especially important in identifying weak, diffuse radio signals that could be associated with dark matter interactions.
Our research focuses on...
Crab-like and Vela-like pulsars are young, rapidly rotating neutron stars with strong magnetic fields. They are noted for their strong pulsed radio and gamma-ray emission and association with pulsar wind nebulae (PWNe). While Crab-like pulsars are generally younger and exhibit bright, compact nebulae, Vela-like pulsars are slightly older and often linked to more diffuse PWNe with complex...
The Kepler KL4040 sCMOS camera by Finger Lakes Instruments was evaluated for its suitability as an affordable alternative to older CCD sensors for optical photometry at the Boyden Observatory. Due to the sensor architecture where each pixel has its own electron to voltage converter, a thorough characterisation and calibration study was conducted to identify key performance factors and...
The trend worldwide is to preserve astronomical photographic plates by digitisation, with some plates dating back to over a century. Indeed, South Africa should be no exception and has a long tradition of observing the night sky of the Southern Hemisphere, initially to produce star charts for improved navigation by seafaring ships. This gave way to observatories for mapping star positions...
Anisotropy is a property of turbulence in solar wind plasma in which velocity and magnetic fields fluctuate along and perpendicular to the ambient magnetic field. Recent in situ measurements confirmed that the solar wind in the inner heliosphere exhibits a temperature anisotropy. The presence of this anisotropy results in magnetohydrodynamic (MHD) waves and instabilities. In this report, we...
Primary cosmic rays are high-energy particles that enter the Earth's atmosphere via the heliosphere, which generate cascades of secondary cosmic-ray particles when interacting with atmospheric atoms. These secondary cosmic-rays interact inversely with hydrogen atoms in soil moisture, providing a non-invasive method for monitoring moisture levels. Continuous measurements of neutron flux in soil...
The C-class solar flare event of 1 July 2012 13:08 UTC was observed in multiple wavelengths by the 1-m Swedish Solar Telescope (SST), providing information about the state of the photosphere, chromosphere and corona. In this study, focus is placed on the changes in sheared photospheric flow pre and post flare. Magnetic features inside the flow pattern are tracked, the borders between several...
Primary cosmic rays are high-energy particles that enter the Earthโs atmosphere via the heliosphere,
which generate cascades of secondary cosmic-ray particles when interacting with atmospheric
atoms. These secondary cosmic-rays interact inversely with hydrogen atoms in soil moisture,
providing a non-invasive method for monitoring moisture levels. Continuous measurements
of neutron flux in...
The Mesosphere and Lower Thermosphere (MLT) region of the upper atmosphere is an essential atmospheric layer that significantly influences energy exchange, atmospheric dynamics, and space weather interactions. Comprehending the temperature of the MLT is essential, as this region acts as a critical interface between Earth's atmosphere and outer space, with its temperature directly affecting...
In this talk, I will show recent results from the deep optical imaging and spectroscopic study of the spectacular nearby galaxy NGC2865.
NGC2865 is well-known for its system of relatively bright stellar shells in the galaxy's outskirts believed to be remnants of a recent merger event. I will, however, unveil a remarkable but hidden stellar feature at the centre of this galaxy which is...
Anisotropy is a property of turbulence in solar wind plasma in which velocity and magnetic fields
fluctuate along and perpendicular to the ambient magnetic field. Recent in situ measurements
confirmed that the solar wind in the inner heliosphere exhibits a temperature anisotropy. The
presence of this anisotropy results in magnetohydrodynamic (MHD) waves and instabilities. In
this report,...
The observation of galactic cosmic ray (GCR) deuteron at the Earth has been done precisely with
the PAMELA and AMS02 space detectors and reported from July 2006 to September 2014 and
from May 2011 to April 2021, respectively. These observations span time frames that include solar
maximum and both minimum modulation conditions in the A > 0 and A < 0 magnetic field cycles
at rigidities...
Enrico Fermi first proposed the stochastic acceleration of protons due to interactions with parsec-scale interstellar magnetic fields as a method of cosmic ray acceleration around the time of the 1950s. Since then, the theoretical framework of stochastic acceleration in magnetohydrodynamic (MHD) turbulence has undergone significant refinement with recent numerical simulations incorporating...
Short gamma-ray bursts (SGRBs) and magnetar giant flares (MGFs) are short gamma-ray transients (SGRTs) with similar temporal profiles but distinct progenitorsโSGRBs arise from compact binary mergers, while MGFs originate from magnetars in nearby galaxies. When MGFs are observed at large distances, their characteristic fading pulses may be undetectable, making them difficult to distinguish from...
The C-class solar flare event of 1 July 2012 13:08 UTC was observed in multiple wavelengths by
the 1-m Swedish Solar Telescope (SST), providing information about the state of the photosphere,
chromosphere and corona. In this study, focus is placed on the changes in sheared photospheric
flow pre and post flare. Magnetic features inside the flow pattern are tracked, the borders...
Active Galactic Nuclei (AGN) play a critical role in regulating and shaping galaxy evolution through various influential processes or mechanisms that impact the surrounding interstellar and intergalactic medium. In dense environments such as galaxy clusters, this interplay becomes even more complex due to environmental effects like ram pressure stripping, tidal interactions, and strangulation....
Gamma-Ray Burst (GRB) afterglows arise from the interaction of relativistic ejecta with the circumburst medium and are observed across the electromagnetic spectrum. Polarisation is expected during the early and late phases of the afterglow depending on the presence of reverse shocks and the viewing geometry of the jet. Polarimetric observations of GRB afterglows serve as a unique diagnostic...
The joint detection of gravitational waves (GW170817) by LIGO and Virgo, together with the short gamma-ray burst (sGRBs) GRB 170817A observed by Fermi and INTEGRAL, has confirmed that at least some sGRBs originate
from the merger of two neutron stars (NS-NS). Despite this breakthrough, the evolutionary pathways that lead to such
mergers remain uncertain.
In this project, we study the...
Among the active galactic nuclei (AGNi), blazars are the brightest emitters of high- (HE, $E \ge 100\,\mathrm{MeV}$) to very-high-energy (VHE, $E \geq 100\,\mathrm{GeV}$) $\gamma$-rays from their jets. Radio galaxies, being the misaligned parent population of the blazar class, were historically not observed at these frequencies. However, there is a growing number of radio galaxies detected in...
The ionosphere is a dynamic, inhomogeneous and conductive plasma formed from the interaction
of solar Extreme Ultraviolet (EUV) and X-ray radiation with the quasi-neutral atmosphere of the
Earth, found at 60 โ1000 km above sea level. With different peak levels of ionization, it is predominantly
studied by determining the total number of particles that pass through a square meter
area...
The diurnal variation of plasma density in the ionosphere is largely characterized by a single peak
around local noon. However, diurnal double maxima (DDM) is sometimes observed when two
distinct peaks and one valley in plasma density appear during the local daytime. Understanding
DDM structures is essential for studying ionospheric dynamics and their key drivers, including
neutral winds,...
This talk will present results of ionospheric changes during the 23-25 March 2023 geomagnetic
storm using observational and modeling data over the African-European sector. Both ionosonde
and Swarm observational results show that mid latitudes experienced negative storm effects which
have been attributed to thermospheric composition changes. We use models to simulate the...
The Earthโs magnetic field plays a critical role in shielding our planet from solar and cosmic radiation,
yet the South Atlantic Anomaly (SAA) region represents a significant weakening of this
protective shield. This research aims to model the temporal and spatial evolution of the SAA
region using the Revised Spherical Cap Harmonic Analysis (R-SCHA) technique, providing improved
regional...
The topside ionosphere is highly sensitive to solar flare activity, which leads to sudden enhancements
in solar X-ray and EUV flux. These enhancements can significantly alter electron density
profiles, impacting satellite communication and navigation systems. This study examines the response
of topside electron density (Ne) to solar flares using in-situ data from the Swarm...
Variations in thermospheric density play an essential role in satellite operations, particularly during
geomagnetic disturbances, where fluctuations in atmospheric drag impact orbital stability. A
significant incident on February 4, 2022, saw SpaceX lose 38 Starlink satellites due to unanticipated
atmospheric drag following a geomagnetic storm. This study aims to identify high- risk periods...
The climate crisis persists, as the global community has yet to fully embrace the actions needed
to tackle it. The decade from 2010 to 2019 was the hottest on record, leading to devastating wildfires,
hurricanes, droughts, floods, and other climate-related disasters worldwide. To limit global
warming to 1.5โ above pre-industrial levels, emissions must already be on the decline and need...
