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dc.contributor.advisorMeintjes, P. J.
dc.contributor.authorVan Soelen, Brian
dc.date.accessioned2015-11-25T10:54:53Z
dc.date.available2015-11-25T10:54:53Z
dc.date.copyright2012-01-30
dc.date.issued2012-01-30
dc.date.submitted2012-01-30
dc.identifier.urihttp://hdl.handle.net/11660/1919
dc.description.abstractEnglish: The high-mass binary system PSR B1259-63/LS 2883 is one of only six known gamma-ray binaries, and the only one where the compact object is known from the direct observation of a pulsed radio signal to be a 48 ms pulsar. During it’s eccentric 3.4 year orbit, the pulsar moves through the circumstellar disc of the optical companion, approximately twenty days before and after periastron. This results in conditions for complicated interactions between the material in the disc, the fast rotating pulsar, the pulsar wind, and the radiation field from the star and disc. The system has been the object of multi-wavelength campaigns with telescopes such as the VLT, H.E.S.S. and Fermi. The interaction between the stellar and pulsar wind results in the formation of a radiating pulsar wind nebula within the binary system, which has been detected from radio to TeV gamma-ray energies. The spectral energy distribution is dominated by the emission at gamma-ray energies, classifying this system as a gammaray binary. The interaction between the stars is greater near periastron where the pulsar passes closest to the optical companion. Approximately twenty days from periastron the pulsar passes through or behind the Be star’s circumstellar disc, obscuring the pulsed radio signal. During this period there is a corresponding increase in the unpulsed emission from the system. The TeV gamma-rays are believed to be produced by electrons in the pulsar wind which cool via the inverse Compton up-scattering of stellar photons from the optical companion. The circumstellar disc associated with the Be star produces an infrared flux below ! 1015 Hz, which is greater than that expected from the blackbody distribution associated with star, providing additional target photons which could increase the inverse Compton scattering rate. The scattering of infrared photons can occur in the Thomson limit with its significantly larger cross-section and should produce GeV energy gamma-rays in the energy range observed by the Fermi telescope. A curve of growth method is presented to model the infrared free-free and free-bound emission from the circumstellar disc, taking into account the changing viewing angle as observed from the pulsar. The curve of growth model is fitted to archive near-infrared and optical data and mid-infrared data obtained with the Very Large Telescope during January 2011. The effect of this infrared excess on the inverse Compton scattering rate is considered for an isotropic and anisotropic photon distribution, considering pre– and post–shock electron distributions. The anisotropic modelling considers the effects of the changing size and orientation of the circumstellar disc relative to the pulsar, as well as the change in the inverse Compton scattering angle during the orbit. The inverse Compton scattering rate for three disc orientations is modelled over a period of approximately 160 days around periastron, including the disc crossing epochs before and after periastron. The maximum disc contribution is found to occur close to periastron and not near the disc–crossing where the low infrared flux from the disc, at a radius of ! 45 stellar radii, has a less significant effect. It is found that the inclusion of the infrared flux from the circumstellar disc can increase the GeV flux from the system by a factor ! 2 near periastron, for favourable disc orientations. The predicted increase is, however, less than was detected with Fermi during the 2011 periastron passage. The observations showed a flare which cannot be explained by this, or any current model.en_ZA
dc.description.abstractAfrikaans: Die ho¨e-massa binˆere sisteem PSR B1259-63/LS 2883 is een van slegs ses bekende gamma-straal binˆere stelsels, en is die enigste sisteem waar die kompakte voorwerp bekend is, naamlik as ’n 48 ms pulsar, soos afgelei vanuit die direkte waarneming van ’n pulserende radio-sein. Tydens die eksentrieke 3.4-jaar baan, beweeg die pulsar deur die sirkumstellˆere skyf van die optiese ster, ongeveer twintig dae voor en na periastron. Dit lei tot gunstige toestande vir ingewikkelde interaksies tussen die materiaal in die skyf, die vinnig-roterende pulsar, die pulsarwind en die stralingsveld van die ster en skyf. Die stelsel is die voorwerp van multi-golflengte veldtogte met teleskope soos VLT, HESS en Fermi. Die interaksie tussen die ster en pulsar winde het ’n pulsar-wind newel tot gevolg binne die binˆere stelsel, wat waargeneem word van radio tot TeV gammastraal energie¨e. Die spektraalenergie verspreiding word gedomineer deur die uitstraling van gammastraal-energie fotone, wat hierdie sisteem klassifiseer as ’n gammastraal binˆere sisteem. Die interaksie tussen die sterre is mees intens naby periastron, d.i waar die pulsar die naaste verbybeweeg aan die optiese ster. Ongeveer twintig dae vanaf periastron beweeg die pulsar deur of agter die Be ster se sirkumstellˆere skyf, waar die gepulseerde radiosein versper word. Gedurende hierdie periode is daar ’n ooreenstemmende toename in die nie-gepulseerde radio uitstraling vanaf die sisteem. Die TeV gammastrale word vermoedelik geproduseer deur elektrone in die pulsarwind, wat deur die inverse Compton proses, ster en skyf fotone opwaarts verstrooi tot baie ho¨e-energie. Die sirkumstellˆere skyf wat geassosieer word met die B-tipe ster, produseer ’n surplus infrarooi vloed, wat groter is as die swartstraling vloed wat geassosieer word met die ster alleen onder die frekwensiegebied ! 1015 Hz, wat addisionele teikenfotone verskaf wat die inverse Compton verstrooiingstempo versnel. Hierdie verstrooiing van infrarooi fotone vind hoofsaaklik plaas in die Thomson-grens met sy aansienlik groter botsingsdeursnit (produksiewaarskynlikheid). Dit veroorsaak dat GeV energie gammastrale meer geredelik geproduseer word in die GeV energie gebied wat moontlik deur die Fermi teleskoop waargeneem kan word. ’n Groeikurwe metode word voorgestel om die infrarooi vry-vry en vry-gebonde emissie van die sirkumstellˆere skyf te modelleer, met inagname van die wisselende besigtigingshoek soos waargeneem vanaf die pulsar. Die groeikurwe model is begrens met beulp van infrarooi en optiese waarnemings, met onder andere die sogenaamde “Very Large Telescope (VLT)” gedurende Januarie 2011. Die effek van hierdie infrarooi surplus op die inverse Compton verstrooiingstempo is in aanmerking geneem vir ’n isotropiese en nie-isotropiese foton verspreiding, inagenome van voor en na-skok elektron versdelings. Die nie-isotropiese modellering neem effekte in ag soos die veranderende grootte en ori¨entasie van die sirkumstellˆere skyf relatief tot die pulsar, sowel as die verandering in inverse Compton verstrooiingshoek gedurende die wentelbaan, veral naby periastron. Die inverse Compton verstrooingstempo vir drie skyf ori¨entasies is gemodelleer oor ’n tydperk van ongeveer 160 dae rondom periastron, insluitend die skyf oorkruising episodes voor en na periastron. Dit is bevind dat die maksimum inverse Compton verstrooiingstempo naby aan periastron plaasvind en nie naby die skyf oorkruising waar die lae infrarooi intensiteit vanaf die skyf, op afstande van ! 45 ster radiusse, nie ’n betekenisvolle effek op die inverse Compton gamma-straal produksietempo het nie. Daar is bevind dat die insluiting van die infrarooi vloed vanaf die sirkumstellˆere skyf die GeV produksietempo vanaf die sisteem met faktor ! 2 verhoog naby periastron vir gunstige skyf ori¨entasies. Die voorspelde verhoging is egter minder as wat deur Fermi waargeneem is gedurende die 2011 periastron. Die waarnemings toon ’n opvlamming wat nie deur hierdie model of enige huidige model verklaar kan word nie.af
dc.description.sponsorshipNational Research Council (NRC)en_ZA
dc.description.sponsorshipSouth African SKAen_ZA
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectThesis (Ph.D. (Physics))--University of the Free State, 2012en_ZA
dc.subjectPulsarsen_ZA
dc.subjectGamma ray astronomyen_ZA
dc.subjectDouble starsen_ZA
dc.subjectX-ray binariesen_ZA
dc.subjectGamma-rays: generalen_ZA
dc.subjectInfrared: starsen_ZA
dc.subjectPulsars: individual: PSR B1259-63en_ZA
dc.subjectRadiation mechanisms: thermalen_ZA
dc.subjectRadiation mechanisms: non-thermalen_ZA
dc.subjectTechniques: photometricen_ZA
dc.subjectStars: emission-line, Been_ZA
dc.subjectStars: individual: LS 2883en_ZA
dc.titleGamma-ray production in the Be-type star-pulsar binary system PSR B1259-63en_ZA
dc.typeThesisen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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