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Th`Ese Etienne POINTECOUTEAU Directeur De Recherche Directeur De Th`Ese THTHESEESE`` En vue de l’obtention du DOCTORAT DE L’UNIVERSITE´ DE TOULOUSE D´elivr´e par : l’Universit´eToulouse 3 Paul Sabatier (UT3 Paul Sabatier) Pr´esent´ee et soutenue le 01/10/2019 par : Edoardo CUCCHETTI De l’astrophysique des amas de galaxies `ala physique des microcalorim`etresen rayons X : performances scientifiques et calibration du X-ray Integral Field Unit de la mission Athena JURY Sophie HENROT-VERSILLE Directeur de Recherche Pr´esidente du jury Jelle KAASTRA Professeur des Universit´es Rapporteur Alessandro MONFARDINI Directeur de Recherche Rapporteur Doreen WERNICKE Ing´enieure Examinateur Franc¸ois PAJOT Directeur de Recherche Directeur de th`ese Etienne POINTECOUTEAU Directeur de Recherche Directeur de th`ese Ecole´ doctorale et sp´ecialit´e : SDU2E : Astrophysique, Sciences de l’Espace, Plan´etologie Unit´e de Recherche : Institut de Recherche en Astrophysique et Plan´etologie (UMR 5277) Directeur(s) de Th`ese : Fran¸coisPAJOT et Etienne POINTECOUTEAU Rapporteurs : Jelle KAASTRA et Alessandro MONFARDINI A tutti coloro che mi sono accanto, per il vostro sostegno e i vostri incoraggiamenti. A tutti coloro che non ci sono più, il vostro ricordo è sempre presente. A tutti, per avermi sopportato e per dover continuare a farlo. Abstract Future breakthroughs in X-ray astronomy require a new generation of X-ray instruments, capable of observing the sky with high spectral and spatial resolutions combined. This need drives the development of the X-ray Integral Field Unit (X-IFU) onboard the future European X-ray observatory Athena, scheduled for a launch in 2031. The complexity of the X-IFU and of its readout chain calls for a close monitoring of its instrumental effects. This can be investigated using dedicated end-to-end simulators, which reproduce an X-ray observation, from the emission of X-rays by an astrophysical source to their detection. In the first part of this thesis, I use this approach to quantify the impact of crosstalk between pixels, to derive the requirement on the reproducibility of the instrumental background, and to estimate the line sensitivity of the instrument. I demonstrate that the X-IFU will be capable of observing bright extended sources with a required high-resolution throughput above 80%. I also show that an accurate knowledge of the spectral lines (their energy and their profile), as well as of the non-X-ray background level (to better than 2%) are needed to minimise systematic errors in the observation. Analysis of the instrumental effects need to be coupled with feasibility studies of the core science objectives of the X-IFU to verify the potential of the instrument. This is valid in particular for extended sources, which will use this integral field unit at its full capabilities. In the second part of this work, I investigate the ability of the X-IFU to characterise the properties of the intra-cluster medium and its turbulent motions. To guarantee a representative result, both toy models and hydrodynamical simulations of clusters are used as inputs of end-to-end simulations. My results underline the strengths of the X-IFU, which will provide an accurate view of the physics and the chemical enrichment of clusters, even at high redshift (z ∼ 2) with typical 100 ks exposure. I also put forward an analytical way to estimate the systematic errors on line diagnostics in turbulence-related studies, which will be of particular interest to optimise future observations. To fulfil its science objectives, the X-IFU will require a careful calibration. The third part of this thesis presents studies on this topic related to the energy scale, the instrumental background, or the quantum efficiency. I demonstrate that new methods of gain drift correction and background monitoring are required to meet the expected requirements. These results provide constraints on the design of the instrument (e.g., modulated X- ray sources, correction strategies) and can be used to plan ground or in-flight calibration activities. Calibration studies will also be performed experimentally, notably using the test bench developed and characterised at IRAP during my thesis. Key words: Calibration – Clusters of galaxies – Cryogenic detection – End-to-end simu- lations – Feasibility studies – Instrumental performance – X-ray astronomy – X-IFU Résumé Des découvertes inédites dans le domaine de l’astronomie en rayons X nécessitent une nouvelle génération d’instruments, pouvant observer le ciel en combinant des hautes réso- lutions spatiales et spectrales. Ce besoin constitue le fondement du X-ray Integral Field Unit (X-IFU) de la mission Athena de l’ESA, dont le lancement est prévu en 2031. La complexité de la chaîne de détection du X-IFU nécessite un suivi de ses perturba- tions instrumentales. Des simulations bout-à-bout, reproduisant les observations en rayons X de l’émission des photons d’une source représentative à leur détection, sont un outil de choix pour ces études. Dans la première partie de cette thèse, j’utilise ces simulateurs pour quantifier l’effet de la diaphonie entre les pixels, pour dériver une spécification sur la connaissance du bruit de fond instrumental, ou encore pour estimer la sensibilité spectrale de l’instrument. Mes résultats confirment que le X-IFU atteindra ses exigences en taux de comptage pour des sources étendues brillantes. Ils démontrent aussi qu’une bonne connais- sance des raies spectrales, ainsi que du niveau bruit de fond instrumental (à mieux que 2%) est indispensable pour éviter des erreurs systématiques dans le traitement des données. L’analyse des performances doit cependant être couplée à des études de faisabilité des objectifs scientifiques du X-IFU. Cela concerne particulièrement les observations de sources étendues, qui feront appel à tout le potentiel de l’instrument. La deuxième partie de ce travail analyse les capacités du X-IFU à caractériser les propriétés physiques et chimiques du milieu intra-amas, ainsi que sa turbulence. Pour obtenir des simulations représentatives, des modèles ou d’autres simulations numériques sont utilisés comme point de départ de ces études. Mes résultats montrent la puissance du X-IFU à mesurer les propriétés des amas de galaxies, même à haut redshift (z ∼ 2) et sur des temps d’exposition de 100 ks. Je présente également une nouvelle façon d’aborder les biais sur les diagnostics spectraux. Elle permettra d’optimiser les observations de la turbulence dans les amas. Enfin, pour remplir ses objectifs scientifiques, le X-IFU nécessitera une calibration très précise. La troisième partie de cette thèse aborde différents points de la calibration du X-IFU, notamment la connaissance de son échelle de gain, de son efficacité quantique et de son bruit de fond instrumental. Je démontre que de nouvelles méthodes de correction de gain et de surveillance du niveau de bruit de fond instrumental sont nécessaires pour vérifier les spécifications attendues. Ces résultats permettent d’optimiser l’architecture de l’instrument (par ex., sources modulées de rayons X, stratégies de corrections) et de mieux préparer ses phases de calibration au sol et en vol. Les études de calibration se feront aussi et surtout par des essais en conditions représentatives, comme dans le banc cryogénique développé et caractérisé à l’IRAP au cours de ma thèse. Mots clés : Amas de galaxies – Astronomie rayons X – Calibration – Détection cryogénique – Études de faisabilité – Performances instrumentales – Simulations end-to-end – X-IFU Contents Acknowledgementsi Avant-proposv Foreword ix 1 An introduction to X-ray astronomy1 1.1 Observing the X-ray sky.............................1 1.1.1 How are X-rays observed?........................1 1.1.2 How are astrophysical X-rays created?.................3 1.1.3 Reminders of spectroscopy........................5 1.1.4 X-ray astronomy.............................6 1.2 The formation of large structures........................8 1.2.1 A brief history of the Universe.....................8 1.2.2 Clusters of galaxies............................9 1.2.3 Thermodynamic and dynamic properties................ 12 1.2.4 A metal-rich intra-cluster medium?................... 17 1.3 Stellar nucleosynthesis and metal enrichment................. 18 1.3.1 The role of stars in metal formation.................. 18 1.3.2 Metal enrichment of the Universe.................... 21 1.4 The energetic phenomena of the Universe................... 24 1.4.1 X-ray as messengers of the energetic Universe............. 24 1.4.2 Understanding the evolution of compact objects............ 25 1.5 Present limits and future challenges in X-ray astronomy........... 26 1.5.1 Open questions in X-ray astronomy................... 26 1.5.2 The need for a new-generation X-ray observatory........... 27 2 The Athena mission and the X-ray Integral Field Unit 29 2.1 The Advanced Telescope for High-Energy Astrophysics............ 29 2.1.1 The Athena mission........................... 29 2.1.2 The Athena mirror assembly...................... 30 2.2 The Wide Field Imager............................. 32 2.2.1 Instrumental design and detection principle.............. 32 2.2.2 Steps forward with the WFI....................... 34 2.3 The X-ray Integral Field Unit.......................... 35 2.3.1 Instrument motivation and design................... 35 2.3.2 TES micro-calorimeter detection principle............... 36 2.3.3 Readout principle............................. 38 2.3.4 Cryogenic anti-coincidence detector................... 44 2.3.5 Cryogenic chain and dewar structure.................. 45 3 Performance and sensitivity studies of the X-IFU 51 3.1 End-to-end simulations using SIXTE...................... 51 3.1.1 Photon generation using SIMPUT files................. 52 3.1.2 Imaging photons............................. 53 3.1.3 Processing the impact list........................ 54 3.2 xifupipeline as a performance simulator................... 54 3.3 Detection chain analysis through tessim and XIFUSIM ............ 55 3.3.1 Detailed TES simulations........................ 55 3.3.2 Additions to tessim and XIFUSIM .................... 60 3.3.3 Simulation of the full detection chain – XIFUSIM ............ 61 3.4 Count rate capability of the X-IFU....................... 61 3.4.1 Grading rejection............................
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