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dc.contributor.advisorVan Soelen, Brian
dc.contributor.advisorMeintjes, Petrus Johannes
dc.contributor.authorVan der Westhuizen, Izak Petrus
dc.date.accessioned2017-09-28T07:08:04Z
dc.date.available2017-09-28T07:08:04Z
dc.date.issued2017-03
dc.identifier.urihttp://hdl.handle.net/11660/7027
dc.description.abstractEnglish: Active regions at the centres of certain galaxies known as Active Galactic Nuclei (AGN) are some of the most energetic and violent sources of emission in the universe. Certain types of AGN can produce jet-like emission structures that extend hundreds of kiloparsec in length. The jet-like sources show intricate time dependent structure and are believed to consist of collimated flows of relativistic plasma. Many studies have focused on investigating the structure and emission of these sources. The evolution time scale of the jets are much longer than their recorded history which makes observational studies of their evolution challenging and, due to the relativistic nature of these jets, they have not been accurately reproduced in laboratory experiments. Instead many studies have employed fluid dynamic numerical simulations of these sources to study their properties. To accurately compare a fluid dynamic simulation to that of observational data the emission emitted by such an environment must be modelled. In this study a fluid dynamic simulations of a relativistic jet is constructed and a synchrotron emission model is applied to the simulations to reproduce intensity maps at radio frequencies which is comparable to observational data of AGN jet sources. The numerical fluid dynamic simulation was created and evolved using the PLUTO software and consisted of a three dimensional environment containing ambient medium, into which a jet is injected through a nozzle on the lower z boundary. The injected material consisted of a less dense medium with a super-sonic bulk motion of Lorentz factor T = 10. The simulation reproduced a jet structure containing a relativistic beam of material propagating through the ambient medium. The beam of material was surrounded by a turbulent cocoon region with asymmetric structure. The entire structure was encased in a bow shock. Intensity maps of the three dimensional fluid simulation were created by applying a post-processing code to the simulation data. The emission model estimated the synchrotron emission by assuming that the entire population of electrons in the jet had a power-law energy distribution. The intensity maps were able to reproduce emission structures that resemble those of FR II type radio galaxies with a dominant cocoon region containing time dependent hot spots and laments. To investigate the effects of Doppler boosting, intensity maps were calculated at different polar angles and the results were consistent with the current unified model of AGN and showed a significant increase in the intensity of the relativistic beam at small polar angels. The intensity maps were able to reproduce time dependent emission structures due to fluid dynamic instabilities that formed during the simulation. The time dependent structure led to the production of variability with an amplitude of ≈ 10% in the total intensity. It was therefore shown that some variability observed within these sources occurs due to fluid dynamic instabilities rather than a change in the injection parameters. However, large flares which have been observed from these sources require additional perturbations in the flow. This study serves as a good basis for future in depth investigation of AGN emission.en_ZA
dc.description.abstractAfrikaans: Die aktiewe gedeeltes in die middel van sommige sterrestelsels wat bekend staan as Aktiewe Galaktiese Kerne (AGK) is van die mees geweldadigste en energieke stralingsbronne in die heelal. Sekere AGK tipes produseer spuitstraal-agtige strukture wat oor honderde kiloparseks kan uitstrek. Die spuitstraalbronne toon ingewikkelde tyd afhanklike strukture en daar word vermoed dat hierdie bronne uit gekollimeerde vloeie van relativistiese plasma bestaan. Baie studies het al die struktuur en straling van hierdie bronne bestudeer om hulle aard beter te verstaan. Die leeftyd van hierdie spuitstrale strek egter oor 'n baie langer tydperk as hulle opgetekende geskiedenis wat waarnemingstudies van die evolusie van die bronne uitdagend maak en, vanwe e hulle relativisties natuur, kon hulle tot dus ver nie gereproduseer word in laboratorium eksperimente nie. As gevolg hiervan het baie studies van die bronne na u eddinamiese rekenaar simulasies gedraai om hulle eienskappe beter te bestudeer. Om die simulasies op 'n akurate wyse met waarnemings te kan vergelyk moet die straling wat hierdie omgewings produseer gemoduleer word. In hierdie studie word daar 'n u eddinamiese simulasie van 'n relativistiese spuitstraal geskep en 'n stralings model word daarop toegepas om intensiteitskaarte wat vergelyk kan word met waargenome data in radio gol engtes te produseer. Die u eddinamiese simulasie het bestaan uit 'n drie dimensionele ruimte wat 'n agtergrond medium in rus bevat het. 'n Relativistiese spuitstraal medium was in die ruimte ingespuit deur 'n spuitstuk op die onderste z-grens. Die simulasie was geskep en ontwikkel met tyd deur gebruik te maak van die PLUTO rekenaar sagteware. Die ingespuitde materiaal het bestaan uit 'n supersoniese medium wat minder dig as die agtergrond medium was met 'n Lorentz faktor van T = 10. Die simulasie het 'n spuitstraal geproduseer met 'n relativistiese gekolimeerde straal wat omring was deur 'n asemetriese, turbulente koekon. 'n Boogskok het gevorm om die hele struktuur en het die spuitstraal van die agtergrond medium geskei. Die intensiteitskaarte was uitgewerk deur 'n na-proseseerings program op die simulasie data toe te pas. Die stralings model in na-proseseerings program het 'n beraming van die sinchrotronstraling uitgewerk onder die aname dat die populasie van elektrone in die spuitstaal 'n magswet verspreiding van energie besit. Die intensiteitskaarte wat uitgewerk was het sootgelyke struktuur getoon aan FR II tipe radio sterrestelsels met 'n dominate koekon wat tydsafhanklike variasies bevat het. Om die e ek van relativistiese groepssnelheid op die gemeete straaling te bestudeer was intensiteitskaarte teen verskillende poolhoeke bepaal. Die resultateaf
dc.description.sponsorshipNational Research Foundation (NRF)en_ZA
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectActive galactic nucleien_ZA
dc.subjectRelativistic hydrodynamicsen_ZA
dc.subjectSynchrotron emissionen_ZA
dc.subjectPLUTOen_ZA
dc.subjectNumerical simulationen_ZA
dc.subjectRadio jetsen_ZA
dc.subjectDissertation (M.Sc. (Physics))--University of the Free State, 2017en_ZA
dc.titleAn investigation of variability and its associated synchrotron emission in relativistic AGN jets using numerical hydrodynamic simulationsen_ZA
dc.typeDissertationen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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