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Simulation d'un télescope Wolter-I grande focale pour l'astronomie X-dur. Application aux projets spatiaux Simbol-X et PheniX.

Abstract : The future of hard X-ray astronomy relies on the development of new instruments able to focus photons of a hundred keV. Indeed, focalization allows an important improvement in sensitivity and angular resolution. Achieved by grazing incidence reflections on Wolter-I mirrors, its use currently limited to tens of keV can be extended to higher energies thanks to a specific coating and a large focal length. As X-ray observations are only possible above the atmosphere, the size of the observatories, and hence their focal length, was limited by the launcher capacity. Over the past few years, different technologies like extendible masts or formation flight have been studied to go beyond this limit. To gain a better understanding of these telescopes, I detail the Wolter-I mirror geometry, their coating reflectivity, the detection in semi-conductor as well as the dynamic related to extendible masts and formation flight. These telescopes are complex optical systems, subject to deformations during observation and need a fine metrology system to measure these deformations for image correction. To study their performance, I developed a code reproducing the real functioning of such a telescope. Each photon is considered individually, its path and interactions depend on the behavior of the telescope structure along with time. Each component of the telescope is modeled, as well as the metrology needed for the restitution of its dynamic. The path of the photon is computed in a three dimensional vector space, using Monte-Carlo methods to reproduce the mirror defaults, their reflectivity and the interactions in the detector. The simulation produces images and energy spectra, from which we can infer the angular resolution, the field of view, the effective area and the detection efficiency. In 2006, the Simbol-X mission was selected in the framework of the formation flight studies. This concept allows a large focal length, the telescope being distributed on two independent spacecrafts. However, the particular dynamic of the formation flight has consequences on the telescope performance and must be controlled. In the framework of this mission, my simulation tool was used to study the consequence of the motion of each satellite on the telescope performance and the influence of the metrology errors on the image reconstruction. This study led to the attitude control specification of each spacecraft and to the metrology accuracy specification. Considering these results, I demonstrate the feasibility of this kind of telescope. Beyond the Simbol-X mission, I have investigated the performance optimization of a hard X-ray telescope. Using my simulation, I have studied the impact of each parameter on the telescope performance. These studies have led to the design of the PheniX project, a telescope operating in the 1-200 keV band, proposed by the Centre d'Etude Spatial des Rayonnements in response to the European Space Agency M3 call. Thanks to a new coating and a large focal length obtained with an extendible mast, this telescope offers a level of performance at 100 keV more than 100 times better than the actual instruments. I present this project and its expected performances in the last part of my thesis.
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Submitted on : Thursday, May 12, 2011 - 3:59:09 PM
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Maxime Chauvin. Simulation d'un télescope Wolter-I grande focale pour l'astronomie X-dur. Application aux projets spatiaux Simbol-X et PheniX.. Planète et Univers [physics]. Université Paul Sabatier - Toulouse III, 2011. Français. ⟨tel-00592473⟩



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