« Study of plasma environment effects on radiative and non-radiative atomic processes involving the K inner-shell in ions of astrophysical interest » par Monsieur Jérôme DEPRINCE

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Le 25 mai 2020 De 15:30 à 19:00

Organisé par

Secrétariat des études

Au vu des mesures de confinement actuelles, la défense aura lieu par vidéo-conférence via le lien suivant : https://bit.ly/JeromeDeprincePublicDefense

Promoteur de la thèse: Monsieur Pascal Quinet et co-promoteur: Monsieur Patrick Palmeri

Résumé de la dissertation:

X-ray K lines emitted by black hole accretion disks are very important lines for astrophysicists. Actually, they have observed widths and shifts that imply an origin very close to the central black hole. Thus, they can be considered as natural probes of the regions very close to the compact object since the intensity and the shape of these lines can give information about the effects of special and general relativity in the emitting region. Moreover, some important properties of the black hole itself, such as its spin, can be inferred by modeling the distortion of the K emission complex.
Plasma conditions in such accretion disks around black holes are thought to be characterized by electronic densities that can be as high as 1022 cm-3. Such high-density conditions may affect the atomic structure and processes corresponding to the ionic species present in the plasma. However, the atomic data used in the standard programs to model astrophysical X-ray spectra are computed assuming an isolated ion approximation. Therefore, this shortcoming is thought to be the major reason for inconsistencies observed in the results.
The main goal of the present PhD work is to estimate the effects of high-density plasma environment on the atomic parameters involved in the K-line emissivities for ions of astrophysical interests (more particularly oxygen and iron), within the context of accretion disks around black holes. In this purpose, relativistic atomic structure calculations have been carried out using the multiconfiguration Dirac-Fock (MCDF) method, in which a time averaged Debye-Hückel potential has been considered for both the electron-nucleus and electron-electron interactions in order to model the plasma environment, using a combination of GRASP2K and RATIP codes.
The detailed and systematic investigation of the atomic structures and processes under high-density plasma conditions has allowed us to obtain a large amount of new radiative and non-radiative parameters involving the K-vacancy states in all oxygen and iron ions. It turned out that the ionization potentials and the K-shell thresholds were the most affected atomic parameters, as a significative lowering of these latter was obtained when considering electron densities from 1018 cm-3 up to 1022 cm-3. This is supposed to play a role in the interpretation of spectra emitted by high-density astrophysical X-ray sources (such as accretion disks around black holes), as far as the ionization balance and K-line emissivities of the plasma are concerned, thus making our work very useful for the analysis of high-resolution spectra that will be recorded with X-ray satellites scheduled for launch in the near future.