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Title: A numerical study in spectra and variability of X-ray binaries and AGN
Author: Rogers, Katrine Sharp
ISNI:       0000 0001 3532 9621
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2008
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A detailed overview of the HEART code is given. This code models radiative transfer of any photon distribution in a plasma of any geometry containing any electron distribution, where the photon and electron distributions evolve simultaneously. All relevant physical processes are included, and applications include modelling the inner regions of X-ray binaries and AGN. An investigation into the capabilities and accuracy of HEART forms the major part of this thesis. HEART is tested for a simple case of a spherical electron plasma where only Compton scattering is modelled and the evolution of the electron distribution is disabled. Tests are done by comparing the output spectra from HEART to the XSPEC model compTT, as well as by using HEART to fit observational data from Cyg X-l. Several additions to the code are also included, some of which are used in the testing process. A limited range of parameters is found to be modelled accurately, and an in- vestigation is included into extending the valid parameter range by including an anisotropic treatment of Compton scattering. HEART is, however, also found to be computer intensive, making it unsuitable for routine spectral fitting. The focus is therefore moved to the capability of HEART for modelling dynamic situations, which is a potential strength of HEART, and may determine whether improvements to the spectral fitting of HEART are worthwhile. Although the framework of HEART allows for dynamic modelling, several mod- ifications are required to implement it. These modifications are implemented and tested by modelling two distinct dynamic situations: a state transition in an X-ray binary and an X-ray burst on the surface of a neutron star. HEART is found to be capable of varying the steady-state parameters from one steady-state to another, but it is not capable of modelling electron heating, reprocessing and energy balance, and it is restricted to modelling very short physical timescales. The limitations discussed above, combined with further technical limitations dis- cussed in this thesis, lead to the conclusion that HEART is not suitable for further use without complete restructuring.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available