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dc.contributor.advisorMeintjes, P. J.
dc.contributor.authorOruru, Bosco
dc.date.accessioned2015-10-27T10:05:04Z
dc.date.available2015-10-27T10:05:04Z
dc.date.copyright2012-04
dc.date.issued2012-04
dc.date.submitted2012-04
dc.identifier.urihttp://hdl.handle.net/11660/1431
dc.description.abstractEnglish: The nova-like variable AE Aquarii consists of a fast rotating magnetized white dwarf, orbiting a late-type main sequence companion star. It is the most enigmatic among cataclysmic variables, and perhaps the best laboratory to study the physics of accretion and related phenomena, due to its multi-wavelength nature and unique flaring activity. The system is in an accretor-propeller state and most of its properties are associated with the propeller process. Using data observed contemporaneously with Chandra and Swift, the UV and X-ray properties of AE Aquarii have been studied. It is shown that the X-ray emission below 10 keV is predominantly soft and characterized by flares and emission lines. The spectra can be reproduced by multicomponent thermal emission models, and the time-averaged X-ray luminosity is determined to be LX 1031 erg s−1. The thermal soft X-ray emission (below 10 keV) is modelled in terms of plasma heating at the magnetospheric radius, where accretion flow from the secondary star interacts with the magnetosphere of the white dwarf. Both UV and X-ray emission are pulsed at the spin period of the white dwarf. The recently detected hard X-ray emission in AE Aquarii (above 10 keV), with a luminosity of LX,hard 6 5 × 1030 erg s−1, shows a non-thermal nature, possible synchrotron emission of high energy electrons in the white dwarf magnetosphere. It is proposed that these electrons are accelerated by large field aligned potentials of V > 1012 V, a process common in the magnetospheres of fast rotating neutron stars, or pulsars. This places AE Aquarii in a unique category with respect to most members of cataclysmic variables. The ratio of the observed hard X-ray luminosity to the spin-down luminosity of the white dwarf in AE Aquarii lies in the range 0.01-0.1 %, which is the same as observed from young rotation-powered neutron stars in the 2-10 KeV range. In this regard, a pulsar-like model is appropriate to explain the origin of the observed non-thermal hard X-ray emission in AE Aquarii.en_ZA
dc.description.abstractAfrikaans: Die nova-tipe veranderlike AE Aquarii bestaan uit ’n vinnig roterende gemagnetiseerde wit dwerg, wat wentel om ’n gevorderde K3-5 hoofreeks ster. Dit is die enigmatiese onder die kataklismiese veranderlikes en dalk ook die beste laboratorium om die fisika van massa-akresie en verwante verskynsels te bestudeer weens die aard van sy multi-golflengte straling en unieke uitbarstings. Die sisteem is in ’n sogenaamde “akresie-propeller”toestand en die meeste van sy multi-golflengte eienskappe word geassosieer met die sogenaamde “propeller”proses. Die UV en X-straal eienskappe van AE Aquarii is bestudeer deur gebruik te maak van die data van gelyktydige waarnemings tussen Chandra en Swift. Dit is bewys dat die X-strale onder 10 keV hoofsaaklik sag is en gekenmerk word deur flikkerings en stralingslyne. Die spektrum kan verklaar word deur multi-komponent termiese stralingsmodelle en die bepaalde tydsgemiddelde X-strale helderheid is LX ∼ 1031 erg s−1 . Die sagte X-strale onder 10 keV is gemoduleer in terme van plasma verhitting by die magnetosferiese radius, soos die massavloed vanaf die sekondˆere ster reageer met die vinnig roterende magnetosfeer van die wit dwerg. Beide die UV en X-straal emissie toon die rotasie modulasie van die wit dwerg. Die harde X-strale in AE Aquarii (bokant 10 keV), met ’n helderheid van LX,hard 6 5 × 1030 erg s −1 , dui op ’n nie-termiese proses, moontlik synchrotron straling van ho¨e-energie elektrone in die wit dwerg magnetosfeer. Die versnelling word veroorsaak deur elektriese potensiale parallel aan die magneetvelde wat groottes van tot V > 1012 V kan bereik, ’n proses algemeen in die omgewings van vinnig roterende neutron sterre of pulsare. Dit plaas AE Aquarii in ’n unieke kategorie met betrekking tot meeste kataklismiese veranderlikes. Die verhouding van die waargenome harde X-straal helderheid tot die totale afrem wenteling luminositeit van die wit dwerg in die AE Aquarii sisteem is tussen 0.01-0.1 %, soortgelyk as wat waargeneem word by jong rotasie-gedrewe neutron sterre tussen 2-10 KeV. In hierdie geval, is ’n pulsar-tipe model toepaslik om die oorsprong van die nie-termiese harde X-strale in AE Aquarii te verklaar.af
dc.description.sponsorshipNational Research Foundation (NRF)en_ZA
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectRadiation: Synchrotronen_ZA
dc.subjectEmission: non-thermalen_ZA
dc.subjectEmission: thermalen_ZA
dc.subjectRotation: white dwarfen_ZA
dc.subjectStars: individual (AE Aquarii)en_ZA
dc.subjectBinary stars: cataclysmic variablesen_ZA
dc.subjectParticle accelerationen_ZA
dc.subjectCataclysmic variable starsen_ZA
dc.subjectWhite dwarf starsen_ZA
dc.subjectThesis (Ph.D. (Physics))--University of the Free State, 2012en_ZA
dc.titleThe propeller driven pulsar-like spin-down and non-thermal emission in the nova-like variable star AE Aquariien_ZA
dc.typeThesisen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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