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Simulations de la caméra d'imagerie grand champ d'ECLAIRS – Modélisation des régions internes des Noyaux Actifs de Galaxies

Abstract : The first part of my thesis deals with the ECLAIRs mission, dedicated to the study of the prompt multi-wavelength emission of Gamma-Ray Bursts (GRBs). The performance of the wide-field X-γ spectro-imager onboard ECLAIRs is computed with Monte-Carlo simulations. The sensitivity to GRB detections depends principally on the background level in the camera. Taking into account the environment at an altitude of 600 km and for a 20o inclination orbit, the background in the imaging energy range (4 to 50 keV) is estimated to be 7.1 counts cm-2 s-1. The limiting sensitivity for a 5.5 σ detection threshold is expected to be 530 mCrab in 1 second in the 4-50 keV energy range. From the level of the background in the 4-300 keV energy range, 50 to 90 GRBs are expected to be detectable per year. From a sample of a hundred GRBs detected in the camera field of view, 47% and 61% of these GRBs should be located with a precision better than 10 and 20 arc-minutes respectively in 1.024 seconds.
With a 105o x 105o field of view and limiting sensitivities of 10 mCrab and 3 mCrab for a 10 h exposure in the 20-200 keV and 3-10 keV energy ranges respectively, the X-γ camera will also survey the sky, to detect X-ray novae, Soft Gamma Repeaters and Active Galactic Nuclei (AGN).

The second part of my thesis concerns the photo-ionisation code Titan for the physical interpretation of XMM-Newton and Chandra high resolution spectra of AGN. Titan computes the radiative transfer 'in a full way', in taking into account the interconnection between matter and radiation, unlike other codes which are dedicated to the interpretation of AGN spectra alone. These codes often use simplified formalisms based on the escape probability. We show evidence that the computation of the radiative transfer 'in a full way' is important to take into account the effects of radiative transfer, and therefore to have a proper interpretation of AGN spectra. Indeed, the use of the escape probability formalism to compute the radiative transfer induces higher line fluxes for the resonant lines, overestimated by approximately 30% for media with a total column density of CD < 1021 cm-2 and up to an order of magnitude higher for media with CD > 1024 cm-2.
A set of spectroscopic diagnostics has been found from a theoretical studies using Titan of the He-like line triplets. These diagnostics allow us to determine the density, the total column density and the ionisation parameters of the observed photo-ionised media, by measuring the fluxes and the radiative recombination continua of the He-like line triplets.
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https://tel.archives-ouvertes.fr/tel-00011955
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Submitted on : Wednesday, March 15, 2006 - 4:01:33 PM
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  • HAL Id : tel-00011955, version 1

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Olivier Godet. Simulations de la caméra d'imagerie grand champ d'ECLAIRS – Modélisation des régions internes des Noyaux Actifs de Galaxies. Astrophysique [astro-ph]. Université Paul Sabatier - Toulouse III, 2005. Français. ⟨tel-00011955⟩

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