The X-ray Observatory Athena is the mission selected by ESA to implement the science theme The Hot and Energetic Universe for L2 (the second Large-class mission in ESA’s Cosmic Vision science programme). One of the two X-ray detectors designed to be onboard Athena is X-IFU (X-ray Integral Field Unit), a cryogenic microcalorimeter based on Transition Edge Sensor (TES) technology that will provide spatially resolved high-resolution spectroscopy. X-IFU will be developed by an international consortium led by IRAP (PI), SRON (co-PI) and IAPS/INAF (co-PI) and involving ESA Member States, Japan and the United States. X-ray photons absorbed by X-IFU detector generate intensity pulses that must be detected and reconstructed on-board to recover their energy, position and arrival time. The software prototype package (SIRENA) in development at IFCA/Spain contains a set of processing algorithms under study to get the best compromise between performance and availability of onboard computing resources. Recently, the baseline for the processing algorithms has been defined selecting the optimal filtering for energy reconstruction and the Single Threshold Crossing as the triggering mechanism. This combined selection provides the best compromise results for the mission requirements, based on the analysis of the simulated data. However, the non-perfect sampling of the pulses rising-edges could result in significant errors of the reconstructed energies with the standard optimal filtering algorithm. If not corrected properly, these errors could induce a prohibitive broadening of the energy resolution. We present here the analysis of the magnitude of this effect and propose a correction. In addition, we evaluate the impact of a reduced readout sampling frequency in the energy resolution, once the jitter correction has been applied.
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