X-rays and Gamma-rays from Cataclysmic Variables: The example case of Intermediate Polar V1223 Sgr

The accretion of matter onto intermediate polar White Dwarfs (IPWDs) seems to provide attractive conditions for acceleration of particles to high energies in a strongly magnetized turbulent region at the accretion disk inner radius. We consider possible acceleration of electrons and hadrons in such region and investigate their high energy radiation processes. It is concluded that accelerated electrons loose energy mainly on synchrotron process producing non-thermal X-ray emission. On the other hand, accelerated hadrons are convected onto the WD surface and interact with dense matter. As a result, high energy $\gamma$-rays from decay of neutral pions and secondary leptons from decay of charged pions appear. We show that GeV-TeV $\gamma$-rays can escape from the vicinity of the WD. Secondary leptons produce synchrotron radiation in the hard X-rays and soft $\gamma$-rays. As an example, we predict the X-ray and $\gamma$-ray emission from IPWD V1223 Sgr. Depending on the spectral index of injected particles, this high energy emission may be detected by the ${\it Fermi}$-LAT telescope and/or the future Cherenkov Telescope Array (CTA) observatory.Comment: 16 pages, 1 figure, accepted to MNRA

Optical and X-ray Properties of CAL 83: I. Quasi-periodic Optical and Supersoft Variability

We have studied the long-term (~ years) temporal variability of the prototype supersoft X-ray source (SSS) CAL 83 in the LMC, using data from the MACHO and OGLE projects. The CAL 83 light curve exhibits dramatic brightness changes of ~1 mag on timescales of ~450 days, and spends typically ~200 days in the optical low state. Combined with archival XMM-Newton X-ray observations these represent the most extensive X-ray/optical study to date of this system, and reveal in much greater detail that the X-ray light curve is anti-correlated with the optical behaviour. This is remarkably similar to the behaviour of the "transient" SSS, RX J0513.9-6951, where the SSS outbursts recur on a timescale of ~168 days, and also anti-correlate with the optical flux. We performed simple blackbody fits to both high and low state X-ray spectra, and find that the blackbody temperature and luminosity decrease when the optical counterpart brightens. We interpret these long-term variations in terms of the limit-cycle model of Hachisu & Kato (2003a), which provides further support for these systems containing massive (~1.3 Msun) white dwarfs. In addition, we have refined their orbital periods in the MACHO and OGLE-III light curves to values of 1.047529(1) days and 0.762956(5) days for CAL 83 and RX J0513.9-6951, respectively.Comment: 9 pages, 8 figures, 3 tables, accepted for publication in MNRA

Optimering van tydreeks-analise-metodes vir veranderlike astrofisiese bronne: AE Aquarii

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Multifrequency Behaviour of the Gamma-Ray Binary System PSR B1259-63: Modelling the FERMI Flare

This paper presents a brief overview of the multifrequency properties of the gamma-ray binary system PSR B1259-63 from radio to very high energy gamma-rays. A summary is also presented of the various models put forward to explain the Fermi "flare" detected in 2011. Initial results are presented of a new turbulence driven model to explain the GeV observations

Teaching problem-solving competency in Business Studies at secondary school level

The high unemployment rate in South Africa compels potential entrepreneurs to start their own businesses in order to survive. Often this is with little or no formal training or education in entrepreneurship. Since problem recognition and problem-solving are amongst the most crucial competencies required for a successful entrepreneurial career, this study aimed to determine whether the application of an extended curriculum with a strong focus on active learning in a business-simulated set-up will enhance this competency. The performance of a specific group of Grade 11 Business Studies learners in this study was measured, both before and after they had been exposed to such an extended curriculum in different experimental settings (intervention). Assessments were done qualitatively through observations and interviews, and quantitatively, by means of question-based scenarios. The findings revealed that the intervention enhanced learners’ entrepreneurial competencies concerning problem recognition and problem-solving considerably. This also contributed to these learners’ positive approach towards Business Studies. In this article, it is argued that practical exposure in a business-simulated set-up will not only result in enhanced entrepreneurial proficiency in school learners, but also contribute to an accelerated pace of economic growth and job creation in our country.Keywords: active learning; business-simulated set-up; entrepreneurship; extended curriculum; problem-solvin

AE Aquarii: A Short Review

The nova-like variable AE Aquarii has been continuously studied since its discovery on photographic plates in 1934. In this short review the peculiar multi-wavelength properties of AE Aquarii will be reviewed and explained in context of its evolution from a high mass transfer phase, during which period it could have been a supersoft X-ray source (SSS)