Study and optimization of the MXT instrument, microchannel X-ray telescope onboard the SVOM space mission

SVOM is a Sino-French space mission to be launched at the end of 2021. Its objective is the study of gamma-ray bursts (GRBs) and other transient high energy sources. These GRBs are very powerful cosmic explosions that can be detected at extreme distances. They appear randomly on all the sky and emit radiation in a wide wavelength range, from the infrared emission to gamma rays. SVOM space mission will shed new light on the physical phenomena associated to GRBs by detecting and observing them in real time over a wide energy range. The satellite, which will be injected on a low Earth orbit, will carry four instruments sensitive from the visible to the gamma-ray domain. Ground based telescopes will complement the space borne ones and will allow for follow-up observations from the visible to the infrared band. The MXT instrument, whose optics are based on the 'lobster eyes' principle, will observe GRBs soft X-rays counterparts (afterglows) between 0.2 and 10 keV. This optics will be used for the first time for an X-ray telescope which means to characterize this optics. MXT will play a key role in the localization of these astrophysical sources that will be transmitted, in real time, to ground based instruments allowing for fast and precise observations. During my thesis, I developed an MXT observation simulator in order to predict the performances of the instrument during the mission. I also developed localization algorithms to be implemented on board the SVOM satellite and made use of the state of the art knowledge about X-ray afterglows in order to predict the localization capabilities of MXT. I demonstrated that 50% of these afterglows will be localized with a better precision than the arc-minute. I finally applied my simulation tools in the case of gravitational wave sources and, in particular, to assess the capabilities of MXT to observe bright X-ray counterparts of binary neutron star mergers. (author)