BEGIN:VCALENDAR VERSION:2.0 PRODID:-//CERN//INDICO//EN BEGIN:VEVENT SUMMARY:Phase-resolved polarimetric constraints on the white dwarf pulsar in AR Sco DTSTART;VALUE=DATE-TIME:20210729T141500Z DTEND;VALUE=DATE-TIME:20210729T143000Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7154@events.saip.org.za DESCRIPTION:Speakers: Louis Du Plessis (NWU\, Potchefstroom\, Department o f Physics)\nMarsh et al.~(2016) detected radio/optical/UV pulsations from the binary system AR Scorpii (AR Sco) mainly at the beat period of $118$~s . This system\, with an orbital period of $3.55$h\, is composed of a cool \, low-mass star and a white dwarf with a spin period of $117$~s. More rec ent observations also showed X-ray pulsations from this source (Takata et al. 2018). Buckley et al.~(2017) found that the polarimetric emission from the white dwarf is strongly linearly polarised (up to $\\sim 40\\%$) with periodically changing intensities. This emission is thought to be powered by the highly magnetised ($5\\times10^{8}$~G) white dwarf that is spinnin g down. We fitted a standard rotating vector model to these polarisation p osition angle data\, and found a magnetic inclination angle $\\alpha\\sim9 0^{\\circ}$ and an observer angle $\\zeta\\sim60^{\\circ}$\, similar to in dependent constraints found by others. Previously we determined that synch rotron radiation dominates other radiation mechanisms for producing the op tical emission as long as the pitch angles of the particles can be maintai ned\; otherwise curvature radiation would dominate. We applied our model t o the orbitally phase-resolved polarisation position angle data from Potte r and Buckley (2018b) and present these results on the evolution of $\\alp ha$ and $\\zeta$ vs. orbital phase. Additionally\, we investigate the evol ution of the linear-flux light curves binned independently at the spin and beat frequency independently vs. orbital phase. Finally we include a Lomb $-$Scargle periodogram for the different regions of the orbital phase ther eby constraining any potential signature of precession in the system.\n\nh ttps://events.saip.org.za/event/206/contributions/7154/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7154/ END:VEVENT BEGIN:VEVENT SUMMARY:Constraining the magnetic field geometry of millisecond pulsar PSR J0030+0451 using NICER and Fermi data DTSTART;VALUE=DATE-TIME:20210729T140000Z DTEND;VALUE=DATE-TIME:20210729T141500Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7144@events.saip.org.za DESCRIPTION:Speakers: Anu Kundu (Centre for Space Research\, North-West Un iversity)\nThe Neutron star Interior Composition Explorer (NICER) was inst alled aboard the International Space Station (ISS) in 2017 with the major aim of a better understanding of the extreme nature and composition of neu tron stars (NSs). With its exceptional sensitivity\, it hopes to constrain the equation of state for these compact objects to high precision. Modell ing thermal X-ray light curves (LCs) of pulsars can also provide us insigh ts into the magnetic field structure of NS which further helps in understa nding the morphology of the surface hot spots.\n \nRecently\, works by [Mi ller et al. (2019)][1] and [Riley et al. (2019)][2] suggested strong evide nce for a multipolar magnetic field of the millisecond pulsar PSR J0030+04 51\, constraining its mass and radius with unprecedented accuracy. [Kalapo tharakos et al. (2021)][3] constrained the parameter space for an offset-d ipole plus quadrupole field configuration\, by calculating polar caps whic h accurately produce the NICER X-ray LC (and inferred surface hotspots) of J0030 making use of Markov chain Monte Carlo (MCMC) methods. This approac h indicates field degeneracies for offset static vacuum and force-free con figurations\, meaning different configurations adequately describe the sam e observed LCs. Exploring the same configuration to fit the gamma-ray LCs measured by Fermi data breaks the field degeneracies – giving a more con strained model solution. \n \nWe are extending the above study by changing the static vacuum field configuration to a more realistic retarded field in terms of a multipole expansion\, where we include higher multipoles\, i .e. beyond quadrupole\, and then including general relativistic effects an d an offset configuration. Exploring the field parameter space by using MC MC for this configuration to fit the X-ray LCs and corresponding Fermi gam ma-ray LCs would help us constrain the field structure\, and eventually th e stellar mass and radii\, more robustly. In the talk\, the impact of this work and future implications would be discussed.\n\n\n [1]: https://ui.a dsabs.harvard.edu/abs/2019ApJ...887L..24M/abstract/\n [2]: https://ui.ads abs.harvard.edu/abs/2019ApJ...887L..21R/abstract\n [3]: https://ui.adsabs .harvard.edu/abs/2021ApJ...907...63K/abstract\n\nhttps://events.saip.org.z a/event/206/contributions/7144/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7144/ END:VEVENT BEGIN:VEVENT SUMMARY:Assessing TeV Visibility of Pulsars DTSTART;VALUE=DATE-TIME:20210729T133000Z DTEND;VALUE=DATE-TIME:20210729T134500Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7142@events.saip.org.za DESCRIPTION:Speakers: Christo Venter (North-west University\, Potchefstroo m Campus)\nRecent detections of the Crab\, Vela\, Geminga pulsar as well a s PSR B1706-44 by ground-based Cherenkov telescopes have created exciting prospects of many more such discoveries by the upcoming Cherenkov Telescop e Array. Pulsed photons with energies in excess of 1 TeV detected from the Crab and Vela pulsars severely constrain the particle energetics\, emissi on mechanisms\, as well as spatial aspects of the dissipation regions with in the pulsar magnetosphere. Within an extended slot-gap framework\, we mo del the broad-band pulsar spectrum invoking force-free-like fields and mul tiple emission components\, including synchro-curvature\, synchrotron self -Compton (SSC) and inverse Compton (IC) radiation by both primary particle s and pairs. IOn particular\, we predict two TeV components: (i) SSC from pairs and (ii) IC from particles accelerated in the current sheet upscatte ring pair synchrotron radiation. We fit our predictions to available broad band data\, indicating that it may now be possible to directly measure the maximum particle energy in pulsars.\n\nhttps://events.saip.org.za/event/2 06/contributions/7142/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7142/ END:VEVENT BEGIN:VEVENT SUMMARY:Eliminating single-band dominance in dual-band pulsar light curve fitting DTSTART;VALUE=DATE-TIME:20210729T134500Z DTEND;VALUE=DATE-TIME:20210729T140000Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7135@events.saip.org.za DESCRIPTION:Speakers: Albertus Seyffert (Centre for Space Research\, North -West University\, Potchefstroom Campus\, 2520 Potchefstroom\, South Afric a)\nThe wealth of multiwavelength pulsar data has stimulated the developme nt of emission models that predict light curves (LCs) over multiple waveba nds\, most notably radio and gamma-ray. Using established statistical meth ods to fit these model LCs to data can prove ineffectual if the data from one waveband are substantially more precise. This waveband—typically rad io—dominates the fit and biases inferred parameters. We re-examine the u se of Pearson's chi-squared statistic for joint fits\, and introduce a new \, derived statistic. The core insight that this statistic encodes is that the component single-band chi-squared values implicitly express goodness of fit in units of the respective LC uncertainties. The resulting implicit weighting the dual-band chi-squared carries is eliminated by expressing t hese values in a shared unit before calculating their sum\, derived by eff ectively standardizing the scaled pulsar-associated flux across the two wa vebands. Importantly\, chi-squared and our new statistic converge to the s ame constraints as the precision disparity dissipates. As a first test\, w e fit two amalgamated dual-band models to 23 Fermi LAT pulsars and compare the resulting constraints to earlier results derived using the same data and similar models. Our fits consistently show no radio dominance\, and ou r constraints more strongly correlate with those derived by eye.\n\nhttps: //events.saip.org.za/event/206/contributions/7135/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7135/ END:VEVENT BEGIN:VEVENT SUMMARY:Shaken\, not stirred: test particles in binary black hole mergers. DTSTART;VALUE=DATE-TIME:20210729T130000Z DTEND;VALUE=DATE-TIME:20210729T131500Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7140@events.saip.org.za DESCRIPTION:Speakers: Pieter Van der Merwe (North-west University\, Center for Space Research)\nIn 2015 the advanced Laser Interferometer Gravitatio nal-Wave Observatory (aLIGO) detected the first ever gravitational\nevent\ , gravitational wave event GW150914\, with multiple new gravitational wave events\, originating from both\nbinary neutron stars and binary black hol e (BBH) mergers\, detected in subsequent years. In light of these detectio ns\,\nwe simulate the dynamics of ambient test particles in the gravitatio nal potential well of a BBH system close to its\ninspiral phase with the g oal of simulating the associated electromagnetic radiation and resulting s pectral energy\ndensity distribution of such a BBH system. This could shed light on possible detection ranges of electromagnetic\ncounterparts to BB H mergers. The potentials are numerically calculated using finite differen ce methods\, under the\nassumption of non-rotating black holes with the po st-Newtonian Paczynski-Wiita potential approximation in tandem\nwith retar ded time concepts analogous to electrodynamics. We find that the frequenci es of potential electromagnetic\nradiation produced by these systems (poss ibly reaching earth)\, range between a few kHz to a few 100kHz. The bulk\n of radiation is distributed at frequencies below 100kHz.\nKeywords: Binary black hole merger\, binary black hole\, binary black hole merger simulati on\, particle acceleration\,\ngravity.\n\nhttps://events.saip.org.za/event /206/contributions/7140/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7140/ END:VEVENT BEGIN:VEVENT SUMMARY:Satellite contamination on Single Dish HI Intensity Mapping with M eerKAT DTSTART;VALUE=DATE-TIME:20210729T131500Z DTEND;VALUE=DATE-TIME:20210729T133000Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7137@events.saip.org.za DESCRIPTION:Speakers: Brandon Engelbrecht (University of the Western Cape) \nNeutral Hydrogen (HI) Intensity Mapping (IM) promises to open a new wind ow for cosmology\, probing Large Scales Structures (LSS) in the Universe o ver a wide range of redshifts. Unfortunately\, HI IM is contaminated by se veral effects\, one of these is the emission from artificial satellites. W e aim to simulate the Radio Frequency Interference (RFI) emitted from the Global Navigation Satellite System (GNSS) for the MeerKAT Single Dish HI I M observations\, focusing on the 1000-1500 MHz frequency range. We fit our satellite model to data taken using the MeerKAT telescope and study the i mpact of the residual contamination in the supposedly RFI free regions.\n\ nhttps://events.saip.org.za/event/206/contributions/7137/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7137/ END:VEVENT BEGIN:VEVENT SUMMARY:A Study of The Lobes of Radio Galaxy Hydra A using MeerKAT Observa tions DTSTART;VALUE=DATE-TIME:20210727T130000Z DTEND;VALUE=DATE-TIME:20210727T131500Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7130@events.saip.org.za DESCRIPTION:Speakers: Mika Naidoo (The University of the Witwatersrand)\nH ydra A is a type I Fanaroff-Riley radio galaxy which hosts a pair of 300-k iloparsec diameter radio lobes that are being powered by the previous powe rful AGN outburst. Radio observations provide us with an excellent probe f or the study of high energy particles residing in the lobes. The MeerKAT r adio telescope carried out observations of Hydra A\, from which we obtaine d radio maps at several frequencies. A spatial analysis of the radio maps reveals a pair of inner lobes and a pair of outer lobes. Using these obse rvations\, we computed the radiative flux densities and combined them with previous results from low frequency VLA observations at 74MHz and 327 MHz . We found that the spectrum in the MeerKAT frequency range is well descr ibed by a power law. We set constraints on the magnetic field strength an d the age of the outer radio lobes through electron spectrum modelling whi ch includes electron ageing.\n\nhttps://events.saip.org.za/event/206/contr ibutions/7130/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7130/ END:VEVENT BEGIN:VEVENT SUMMARY:Simulating the enrichment of cosmological gas DTSTART;VALUE=DATE-TIME:20210729T094500Z DTEND;VALUE=DATE-TIME:20210729T100000Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7124@events.saip.org.za DESCRIPTION:Speakers: Renier Hough (North-West University)\nLarge\, state- of-the-art cosmological simulations allow us to follow the evolution of va rious galaxies\, and since it contains detailed knowledge of e.g. the meta l content of the stars in each galaxy\, it can be used to compare to galax ies in the real Universe. In our work\, we are improving the implementatio ns of the stellar feedback model within the GIZMO-Mufasa cosmological simu lation. This particular simulation is the merged product of GIZMO's public available code and Mufasa/SIMBA to create realistic large-scale enviromen ts. Specifically\, we are improving the current simplistic instantaneous r ecycling of the metals model\, with a more accurate Cosmic Chemical Enrich ment model developed by Kobayashi et al (2007) and updated in Kobayashi et al (2020). This will improve the time delay due to the star's evolution a nd the time delay for the local enrichment to occur\, as well as add new m etals to the evolutionary tracks of stars tracked by simulations. We added a probability distribution to determine if a specific region will be enri ched (rather than a fixed distance distribution) into the mechanical feedb ack process. This distribution can be found in the thermal feedback proces s in the main GIZMO simulation. This will lead to more realistic black hol e seedings. Ultimately\, we can compare the new model to the old simplisti c model using various different well-tested scenarios (e.g Mass-Metallicit y relation) and interpret any differences.\n\nhttps://events.saip.org.za/e vent/206/contributions/7124/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7124/ END:VEVENT BEGIN:VEVENT SUMMARY:Bow shocks formed by massive runaway stars in 3D DTSTART;VALUE=DATE-TIME:20210729T103000Z DTEND;VALUE=DATE-TIME:20210729T104500Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7156@events.saip.org.za DESCRIPTION:Speakers: Katlego Ramalatswa (University of Cape Town)\nHyper- runaways are stars moving at supersonic speeds through the interstellar me dium\; they can be thought of as a subset of runaway stars but moving with velocities that are comparable to the Galactic escape velocity $(\\sim 50 0\\\,$km/s). Because of the strong stellar winds and high space velocities \, we expect massive (hyper)runaway stars to produce bow shocks. We use PL UTO\, a magneto-hydrodynamics grid code\, to simulate these bow shocks\, p erforming axi-symmetric hydrodynamic simulations in 3-dimensions while inc luding thermal conduction and detailed radiative cooling processes. In thi s talk we will present our results for a range of stellar velocities ($10 0 \\leq v_{\\rm star} \\leq 500\\\,$km/s) and discuss the implications for potentially observing hyper-runaways.\n\nhttps://events.saip.org.za/event /206/contributions/7156/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7156/ END:VEVENT BEGIN:VEVENT SUMMARY:Capturing Transients -- From Biostatistics to Astronomy DTSTART;VALUE=DATE-TIME:20210729T104500Z DTEND;VALUE=DATE-TIME:20210729T110000Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7147@events.saip.org.za DESCRIPTION:Speakers: Anke van Dyk (University of Cape Town/SAAO)\nCapture -recapture has been identified as a possible use case for estimating the u nderlying size of astrophysical transient and variable populations. We pre sent a series of exploratory analyses using capture-recapture methods from biostatistics. Several estimators were tested for their applicability. W e implemented two different capture-recapture approaches: a statistically closed population and a robust design\, a mixture of closed and open popul ation modelling. \n\nIn the first approach\, we used simulations of the X -ray lightcurves of high mass X-ray binaries (HMXBs) to probe the converge nce to the input population for several estimators as a function of the nu mber of observations. The cadence played a crucial role in the rate of con vergence to the underlying population with respect to the number of observ ations relative to the underlying period distribution of the recurrent sou rce outbursts. The cadence and threshold discrimination of sources between outburst and quiescent states affect the capture probability of sources. Capture probability was demonstrated to be a key factor for population est imation\, categorised into 'behavioural'\, 'temporal'\, and 'heterogeneous ' effects. The simulations were extended to a real data application for HM XBs in the Small Magellanic Cloud using the OGLE-IV XROM survey. The obser vations were grouped into a fixed number of samples\, and the optical char acteristics included large variation in quiescent flux that creates hetero geneous population capture probability. The estimation was notably limited by the observational flux threshold in this instance.\n\nThe robust desig n investigated a population of Dwarf Nova identified from the OGLE-II\, -I II\, and -IV phases. New individuals were added to the monitoring sample b etween phases\, which the robust design accounts for in its modelling\, an d abundances were estimated within phases and for the entire study. \n\nTh ese investigations have opened a course for population estimation of trans ients and variable stars alongside population synthesis simulations. The g eneration of capture histories remain non-trivial through the choice of ob servation grouping\, brightness scale\, and imposed flux threshold. Recomm endations are made for further exploration of the topic.\n\nhttps://events .saip.org.za/event/206/contributions/7147/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7147/ END:VEVENT BEGIN:VEVENT SUMMARY:Spatio-Kinematics of the Massive Star Forming Region NGC6334I duri ng a Episodic Accretion Event DTSTART;VALUE=DATE-TIME:20210729T100000Z DTEND;VALUE=DATE-TIME:20210729T101500Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7145@events.saip.org.za DESCRIPTION:Speakers: Jakobus Vorster (Centre for Space Research)\nIn 2015 \, the massive protostellar cluster NGC6334I-MM1 flared in various maser s pecies detected by long term monitoring at HartRAO. Followup infrared\, mi llimetre and centimetre observations confirmed that a massive protostar MM 1B (M ~ $6.7 M_\\odot$) inside the cluster underwent a period of high mass gain\, an accretion burst. To probe the effects of such a transient event on the native protostellar environment\, multi-wavelength\, multi-epoch a nd multi-scale observations are required. We present high-resolution relat ive proper motion observations of highly variable water masers in NGC6334I during the onset of the accretion burst. High veloctiy ($\\bar{v} = 85$ k ms$^{-1}$) proper motions were detected in five regions\, CM2-W2\, MM1-W1\ , MM1-W3\, UCHII-W1 and UCHII-W3. Using velocity variance and covariance a nalysis\, we calculated the position angle of the major axis of motions to be -79.4$^\\circ$ centred on MM1B\, showing the axis of the jet driving t he CM2-W2 shock. The axis traced by water maser motion correspond to an ou tflow previously detected in CO emission. Complex motions in MM1-W1 indica te possible turbulent interactions between multiple outflows centred on MM 1. Unpublished high resolution water maser maps of the period before\, dur ing and after the accretion burst will also be presented\, showing the lar ge effects of these bursts on protostellar environments.\n\nhttps://events .saip.org.za/event/206/contributions/7145/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7145/ END:VEVENT BEGIN:VEVENT SUMMARY:A Monte Carlo simulation study of the excitation of molecules in h igh mass star forming regions DTSTART;VALUE=DATE-TIME:20210729T101500Z DTEND;VALUE=DATE-TIME:20210729T103000Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7143@events.saip.org.za DESCRIPTION:Speakers: Lebogang Mfulwane ()\nAstronomical maser emission oc curs in various astrophysical environments and can be used to infer the ph ysical properties of the regions where they are excited. An import part of interpreting the presence of maser emission associated with a specific as trophysical environment is knowing what the pumping mechanism (radiative o r collisional) for a particular maser is. Based on calculations using the online RADEX facility\, Baan et al (2017) recently concluded that the extr agalactic $4.8$GHz formaldehyde megamasers are radiatively pumped. This is contrary to the conclusion of van der Walt (2014) that formaldehyde maser s associated with high mass star forming regions are collisionally pumped. Since much of the interpretation of the maser emission depends on pumping mechanism\, we revisited the pumping of the formaldehyde masers (1) to tr y to understand the results obtained by Baan et al (2017) using the RADEX facility and (2) to extend the calculations of van der Walt (2014) to also include parts of parameter space considered by Baan et al (2017) but not by van der Walt (2014). Some preliminary results\, which suggest that the formaldehyde masers are indeed collisionally pumped\, are presented.\n\nht tps://events.saip.org.za/event/206/contributions/7143/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7143/ END:VEVENT BEGIN:VEVENT SUMMARY:Galaxy Evolution in the Local Universe: Studying the Complete Loca l-Volume Groups Sample (CLoGS) DTSTART;VALUE=DATE-TIME:20210729T093000Z DTEND;VALUE=DATE-TIME:20210729T094500Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7127@events.saip.org.za DESCRIPTION:Speakers: Clinton Stevens (Centre for Space Research\, North-W est University)\nMore than half of all galaxies within the local Universe are found within group environments. Therefore\, galaxy groups are excelle nt laboratories for studying galaxy evolution in the local Universe. The C omplete Local Volume Groups Sample (CLoGS) is the first statistically comp lete galaxy group survey in the optical\, X-ray and radio bands\, consisti ng of 53 galaxy groups and 1427 member galaxies in total. The basic proper ties of the member galaxies\, such as their morphologies\, star formation rates\, stellar masses and radio emission have been determined and studied with regards to their unique group environments. Exciting statistical rel ations between the properties of the member galaxies and their group envir onments have been found\; such as trends in star formation that relate to each group's dynamical age\, X-ray halo and radio emission from their brig htest group ellipticals (BGEs). As a continuation of this study\, a detail ed optical spectroscopic study of these BGEs using data obtained on SALT ( Southern African Large Telescope) is currently underway. The determined st atistical relations and latest spectroscopy results will be presented.\n\n https://events.saip.org.za/event/206/contributions/7127/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7127/ END:VEVENT BEGIN:VEVENT SUMMARY:Potential of the MeerKAT telescope to detect the stimulated decay of axion-like particles DTSTART;VALUE=DATE-TIME:20210727T133000Z DTEND;VALUE=DATE-TIME:20210727T134500Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7159@events.saip.org.za DESCRIPTION:Speakers: Ahmed Ayad (University of the Witwatersrand)\nThe na ture of the cold dark matter (CDM) can be understood by looking for light scalar candidates such as axion-like particles (ALPs). The coupling betwe en ALPs and photons allows for the spontaneous decay of ALPs into pairs of photons. However\, the rate of this process is believed to be small enoug h to be ignored on cosmological timescales. Furthermore\, it has been clai med in several recent works that ALPs can gravitationally thermalize and f orm macroscopic condensates. The stimulated decay of the ALP condensates i s also possible with a significantly high rate. Consequently\, the photon occupation number can receive Bose enhancement and grows exponentially. Th is can lead to radio emissions produced from this process and could be obs erved by the forthcoming radio telescopes. In this work\, we investigate t he detectability of such a radio signature from some astrophysical targets using the MeerKAT radio telescopes. This might provide indirect evidence for the existence of the CDM ALPs.\n\nhttps://events.saip.org.za/event/206 /contributions/7159/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7159/ END:VEVENT BEGIN:VEVENT SUMMARY:Dark-fluid constraints of shear-free universes DTSTART;VALUE=DATE-TIME:20210727T140000Z DTEND;VALUE=DATE-TIME:20210727T141500Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7136@events.saip.org.za DESCRIPTION:Speakers: Maye Elmardi (Center for Space Research\, NWU)\nWe p resent the evolutionary constraints of shear-free cosmological solutions i n the presence of a dark fluid. After describing the general evolution and constraint equations for *quasi-Newtonian* and *anti-Newtonian* spacetime s\, we derive\, at the level of linear perturbations\, the conditions for the existence and consistent evolution of such spacetimes when they are e ndowed with the Chaplygin gas which mimics a unified description of dark m atter and dark energy.\n\nhttps://events.saip.org.za/event/206/contributio ns/7136/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7136/ END:VEVENT BEGIN:VEVENT SUMMARY:Using Asymptotic Matching to Study Accretion Disks DTSTART;VALUE=DATE-TIME:20210727T134500Z DTEND;VALUE=DATE-TIME:20210727T140000Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7123@events.saip.org.za DESCRIPTION:Speakers: Justine Tarrant (University of the Witwatersrand)\nG enerally\, one expects to find accretion disks around massive objects sinc e their gravity is able to pull in surrounding gas\, dust\, etc. toward t hemselves. Such astrophysical objects include black holes and their binari es. However\, as of yet\, no circumbinary disks have been found around ins piralling stellar-mass black hole binaries related to LIGO events. Our aim is to try find a mechanism to explain why this is the case. We start by a ssuming that these binaries do indeed possess a circumbinary disk initiall y but that they\, through some as yet-to-be-determined mechanism\, lose th eir disk by the time the LIGO-observable inspiral begins. We perform a com putational study of a Kerr binary black hole system\, for masses in the LI GO regime. We do this to derive some properties of the circumbinary accre tion disk. This is possible using a novel approach to numerical relativity calculations where the disk dynamics are studied with the help of recentl y developed analytical spacetime models. In this talk we discuss two types of analytical models which may be used to study the geodesics relating to two different metrics. That is\, we compare asymptotic patching vs. asymp totic matching\, which is used to build a global metric from subdivided me tric pieces. We discuss preliminary results.\n\nhttps://events.saip.org.za /event/206/contributions/7123/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7123/ END:VEVENT BEGIN:VEVENT SUMMARY:Diffusing assumptions in astroparticle physics DTSTART;VALUE=DATE-TIME:20210727T141500Z DTEND;VALUE=DATE-TIME:20210727T143000Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7122@events.saip.org.za DESCRIPTION:Speakers: Michael Sarkis (University of the Witwatersrand)\nPr evious calculations of diffuse radio emissions from dark matter annihilati ons have made use of Green’s function approximations to solve the diffus ive cosmic ray transport equation. Some notable astrophysical code package s\, including GALPROP and DRAGON\, take a numerical approach to this calcu lation that involves the use of the Crank-Nicolson finite-differencing sch eme. In this work we analyse the physical accuracy of the analytic approxi mations and directly compare the computational efficiency of the two solut ion methods. We also incorporate full spatial dependence into the diffusio n and energy-loss coefficients\, and compare this to the approach of using spatially-averaged values of the magnetic field strength and thermal elec tron population.\n\nhttps://events.saip.org.za/event/206/contributions/712 2/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7122/ END:VEVENT BEGIN:VEVENT SUMMARY:Probing Dark Matter in the Madala Model using MeerKAT DTSTART;VALUE=DATE-TIME:20210727T131500Z DTEND;VALUE=DATE-TIME:20210727T133000Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7121@events.saip.org.za DESCRIPTION:Speakers: Ralekete Temo (School of Physics and Centre for Astr ophysics\, University of the Witwatersrand)\nThe Madala model was introduc ed to explain several anomalies observed at the Large Hadron Collider. Thi s model introduces a dark matter candidate through the extension of the st andard model’s Higgs-sector\, i.e. heavier scalar bosons are introduced\ , which can couple to dark matter. The cosmic ray spectra and galactic cen tre's gamma-ray flux excesses have been observed in the AMS-02 and Fermi-L AT experiments\, respectively. Assuming the Madala model can explain these excesses\, the aim is to make synchrotron emission predictions for MeerKA T observations. The region of interest for the predictions is the nearby s atellite Reticulum II. The MeerKAT predictions will instigate the validati on of our assumption and otherwise allow us to constrain the particle prop erties of the Madala model from an astrophysical standpoint. In essence we are able to describe the multi-lepton anomalies at the LHC and the anomal ies in astrophysics simultaneously.\n\nhttps://events.saip.org.za/event/20 6/contributions/7121/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7121/ END:VEVENT BEGIN:VEVENT SUMMARY:Modelling the Spectral Energy Distributions and Multi-Wavelength P olarisation of Blazars DTSTART;VALUE=DATE-TIME:20210727T100000Z DTEND;VALUE=DATE-TIME:20210727T101500Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7155@events.saip.org.za DESCRIPTION:Speakers: Hester Schutte (NWU Potchefstroom)\nThe radio throug h optical/UV/X-ray emission from blazars is dominated by highly polarised synchrotron emission from relativistic electrons in their jets. The total degree of polarisation is a composition of the polarised non-thermal synch rotron emission and thermal unpolarised emission components from the dusty torus\, host galaxy\, emission lines from the broad line region (BLR) and accretion disk. For some blazars the accretion disk is not directly obser ved as it is outshone by synchrotron emission. However\, it reveals its pr esence through a decrease of the optical polarisation degree towards highe r frequencies in spectropolarimetry observations\, where the disk is dilut ing the synchrotron polarisation. Considering a leptonic model\, the high -energy X-ray and gamma-ray emission can be modelled as polarised synchrot ron self-Compton radiation which is diluted by Compton up-scattering of un polarised external radiation fields of the BLR and accretion disk. A model is constructed that simultaneously fits spectral energy distributions and multi-wavelength polarisation of blazars. A target-of-opportunity\, Large Science program "Observing the Transient Universe" from the *Southern Afr ican Large Telescope*\, provides spectropolarimetry data for flaring blaza rs in the optical-UV regime. This program includes co-ordinated multi-wave length observations from the *Las Cumbres Observatory*\, the *Swift*-XRT a nd the *Fermi*-LAT. We present results for the flat spectrum radio quasar 4C+01.02 ($z=2.1$)\, for which we constrained its black hole mass as $4 \ \times 10^8 \\\; M_{\\odot}$ and obtained a scaling factor that is indicat ive of the degree of order of the magnetic field (and dependent on line-of -sight) in the emission region.\n\nhttps://events.saip.org.za/event/206/co ntributions/7155/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7155/ END:VEVENT BEGIN:VEVENT SUMMARY:A multi-band view on the evolution of group central galaxies DTSTART;VALUE=DATE-TIME:20210727T104500Z DTEND;VALUE=DATE-TIME:20210727T110000Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7151@events.saip.org.za DESCRIPTION:Speakers: Konstantinos Kolokythas (North-West University)\nMuc h of the evolution of galaxies takes place in groups that occupy the inter esting intermediate-mass range\, where feedback has the greatest impact on galaxy formation and evolution. By using multi-band data (FUV\, Mid-IR\, Radio\, CO\, and X-rays)\, and an optically selected\, statistically compl ete sample of 53 groups (< 80 Mpc\; CLoGS sample) the galaxy evolution and star-formation activity of the central group dominant early-type galaxies is examined in relation to their gas content\, AGN activity and local env ironment. The majority of the group dominant galaxies (87%\; 41/47) are fo und to be passive systems without any significant star-forming activity\, with the rest of the highest star-forming systems found to present signifi cant cold gas detections\, residing in X-ray faint groups (X-ray halo <65 kpc) and none hosting a powerful radio source (P1.4GHz>10^23 W/Hz). As gal axy groups are a favorable environment for both cooling flows and gas-rich galaxy mergers and interactions\, the significant role of both processes on the origin of cold gas and the fuelling of an AGN or star-formation wil l be discussed along with results on the properties of the highest star-fo rming systems and the implications on AGN feedback in galaxy groups.\n\nht tps://events.saip.org.za/event/206/contributions/7151/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7151/ END:VEVENT BEGIN:VEVENT SUMMARY:Monte-Carlo Applications for Partially Polarized Inverse External- Compton Scattering (MAPPIES) DTSTART;VALUE=DATE-TIME:20210727T094500Z DTEND;VALUE=DATE-TIME:20210727T100000Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7139@events.saip.org.za DESCRIPTION:Speakers: Lente Dreyer (North-West University)\nThe spectral e nergy distributions (SEDs) of some blazars exhibit an ultraviolet (UV) and /or soft Xray excess\, which can be modelled with different radiation mech anisms. Polarization measurements of the UV/X-ray emission from blazars ma y provide new and unique information about the astrophysical environment o f blazar jets and could thus help to distinguish between different emissio n scenarios. I will present a new Monte-Carlo code – MAPPIES (Monte-Carl o Applications for Partially Polarized Inverse External-Compton Scattering ) – for polarization-dependent Compton scattering. I will present the co de by showing results of the polarization signatures in a model where the UV/soft X-ray excess arises from the bulk Compton process. Predictions of the expected polarization signatures of Compton emission from the soft X-r ay excess in the SED of AO 0235+164\, and the UV excess in the SED of 3C 2 79 are made for upcoming and proposed polarimetry missions.\n\nhttps://eve nts.saip.org.za/event/206/contributions/7139/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7139/ END:VEVENT BEGIN:VEVENT SUMMARY:Simulations of Stochastic Long-Term Variability in Leptonic Models for External-Compton and Synchrotron Self-Compton Dominated Blazars DTSTART;VALUE=DATE-TIME:20210727T101500Z DTEND;VALUE=DATE-TIME:20210727T103000Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7133@events.saip.org.za DESCRIPTION:Speakers: Hannes Thiersen (NWU)\nIn this talk we present an in vestigation into the nature of\n multi-wavelength variability of blazar s from a purely numerical approach.\n We use a time-dependent one-zone leptonic blazar emission model to\n simulate multi-wavelength variabili ty by introducing stochastic parameter\n variations in the emission reg ion. These stochastic parameter variations\n are generated by Monte Ca rlo methods and have a characteristic power law\n index\, $\\alpha=-2$ in their power spectral densities (PSDs). We include\n representative b lazar test cases for a flat spectrum radio quasar (FSRQ)\n and a high s ynchrotron peaked BL Lacertae object (HBL) for which the high\n energy component of the Spectral Energy Distribution (SED) is dominated by\n e xternal Compton (EC) or synchrotron self-Compton (SSC) emission\n respe ctively. The simulated variability is analyzed in order to\n character ise the distinctions between the two blazar cases and the type of\n pro genitor variations. We show that the variability's power spectrum is\n closely related to underlying progenitor variations for both cases.\n Distinct differences between the different progenitor variations are\n present in the multi-wavelength cross-correlation functions.\n\nhttps://ev ents.saip.org.za/event/206/contributions/7133/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7133/ END:VEVENT BEGIN:VEVENT SUMMARY:Optical emission line properties of some little-known Narrow Line Seyfert 1 galaxies DTSTART;VALUE=DATE-TIME:20210727T103000Z DTEND;VALUE=DATE-TIME:20210727T104500Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7131@events.saip.org.za DESCRIPTION:Speakers: Bynish Paul (Dept. Physics\, University of Johannesb urg & SAAO)\nWe analyse medium resolution optical spectra of six Active Ga lactic Nuclei (AGN)\, with strong iron emission spectra and characteristic s associated with the class referred to as Narrow-Line Seyfert 1 (NLS1) ga laxies. These were observed using the 1.9 m telescope at the South African Astronomical Observatory in Sutherland. The objects are among the brighte r sources of that description accessible from the southern hemisphere: Fai rall 265\, NPM1G $-$15.0297\, CTS J03.19\, EUVE 0414$-$596\, A 644-1\, and HE 2116$-$3609. For each target we performed multiple integrations totall ing between 1 and 2.5 hours\, yielding spectra in the range $\\sim$ 3700-6 000 A with relatively high signal-to-noise ratios. This enabled us to loca te multiple spectral emission features\, including the strong Fe II bands in the range 4000-5400 A as well as other prominent emission lines associa ted with the Balmer series\, Helium and the [O III] nebular doublet. Our m easurements include the flux\, the width and peak wavelength shifts of the lines\, which sometimes displayed multiple components. We describe the pr operties of our sample\, compare these to other representatives of the NLS 1 class and interpret their physical mechanism in the context of AGN theor y.\n\nhttps://events.saip.org.za/event/206/contributions/7131/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7131/ END:VEVENT BEGIN:VEVENT SUMMARY:Time-Dependent Modeling of Blazar Spectral Variability with Diffus ive Shock Acceleration DTSTART;VALUE=DATE-TIME:20210727T093000Z DTEND;VALUE=DATE-TIME:20210727T094500Z DTSTAMP;VALUE=DATE-TIME:20261010T195759Z UID:indico-contribution-416-7128@events.saip.org.za DESCRIPTION:Speakers: Markus Bottcher (University of North West)\nJets in blazars are an excellent forum for studying acceleration at relativistic \ nMHD shocks\, since this process is likely to spawn the highly-variable em ission \nseen across the electromagnetic spectrum from radio to gamma-rays . Our recent \nwork on combining time-dependent multi-wavelength leptonic emission models with \ncomplete simulated thermal + non-thermal particle d istributions from shock \nacceleration theory has resulted in new insights into plasma conditions in \nAGN jets. This has demonstrated the ability t o infer the plasma density\, and \nsuggested the interpretation that turbu lence levels decline with remoteness from \njet shocks\, with a significan t role for non-gyroresonant diffusion. Using our \ntime-dependent two-zone construction\, we are able to model together both extended\, \nenhanced e mission states from larger radiative regions\, and prompt flare events \ni n select Fermi-LAT and TeV blazars. In this contribution\, I present recen t\napplications of this simulation framework to AstroSAT and multi-wavelen gth\nobservations of the prototypical VHE gamma-ray blazar 1ES 1959+650 an d \nNuSTAR and multi-wavelength observations of the high-redshift FSRQ PKS 0537-286. \nA prime goal is to ascertain whether such flares are truly as sociated with prompt \nshock acceleration activity in relatively confined regions. The results illustrate \nhow parametric degeneracies in shock acc eleration conditions can lead to refined \ndeterminations of the plasma de nsity and particle diffusion character in blazar jets.\n\nhttps://events.s aip.org.za/event/206/contributions/7128/ LOCATION:North-West University Potchefstroom Campus URL:https://events.saip.org.za/event/206/contributions/7128/ END:VEVENT END:VCALENDAR