Congratulations to Florent Castellani who defended his thesis

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Portrait of Florent Castellani who defended his thesis


Congratulations to Florent Castellani who defended his thesis entitled “Study of the scientific and instrumental performances of Athena’s X-Ray Integral Field Unit”, on Friday November 17, 2023 at IRAP. This research work was supervised by Francois Pajot and Etienne Pointecouteau.


“The Hot and Energetic Universe is at the heart of X-ray astronomy. Observations in this spectral band make it possible to study, for example, the emission of hot gas contained in galaxy groups and clusters, that of black hole accretion disks, or that of stellar explosions. Spatially resolved high-resolution X-ray spectroscopy will push back the limits of current observatories with hyperspectral images of these astrophysical phenomena. The X-ray Inte- gral Field Unit (X-IFU), aboard the European Space Agency (ESA) future satellite Athena, will be a spectro-imager in the 0.2 – 12 keV energy band, with resolution from 2.5 eV up to 7 keV, using superconducting micro-calorimeters: Transition Edge Sensor (TES).
In this thesis, I present my work on the study of the scientific and instrumental performances of the X-IFU. In the first part, I describe a feasibility study of one of the scientific cases of the mission: the physical characterization of the distant galaxy groups. Using numerically mock observations of the instrument, I have reconstructed the thermodynamic and chemical characteristics using a forward-modeling method fitted with an MCMC. The recovered char- acteristics are then compared with those of the input physical system to assess the scientific capabilities of the instrument. The results show that the X-IFU, in its current configura- tion, can reconstruct the three-dimensional thermodynamic profiles of a group of galaxies (M < 10^14 M⊙) at high redshift (z = 2) with a 100 ks exposure time. This study showed the importance of taking into account the dispersion of thermodynamic quantities in the 3D radial profiles of the galaxy group, which leads to a strong dispersion of projected quantities along the line-of-sight.
In the second part of the thesis, I present my participation in the development of a cryogenic test bench, developed at IRAP with CNES, called the “50 mK test bench”. It features a cryostat for operating TES detectors and their complete electronic detection and readout chain. A complete chain, developed at NASA/GSFC and NIST, has been temporarily in- stalled to evaluate the performance of the test bench. The elements of the current readout chain will be progressively replaced by demonstration models of the X-IFU readout chain. After electromagnetic compatibility progress, the results show that the 50 mK test bench is ready to receive these demonstration models for functional validation of the complete X-IFU reading chain.
The third section describes my contribution of the functional validation of the X-IFU readout chain’s first prototype: the row addressing and synchronization (RAS) module. The success of this operation shows that IRAP’s cryogenic test bench is a suitable tool for studying the performance of the readout chain of the X-IFU. It will subsequently be used to validate the X-ray sources used to calibrate the instrument.”

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