Status of the Cryogenic Anti-Coincidence Detector (CryoAC) for the Athena X-Ray Integral Field Unit (X-IFU)

The Cryogenic Anti-Coincidence detector (CryoAC) is a critical component of the Athena X-ray Integral Field Unit (X-IFU), in order to fully exploit the instrument performance in the pursuit of high-resolution X-ray spectroscopy with Transition Edge Sensor (TES) detectors.Athena will be the upcoming large X-ray observatory by the European Space Agency (ESA) spanning the energy range of 0.2 to 12 keV. Recently, the mission has successfully undergone a redefinition process to align with new parameters set by ESA, and the launch is now scheduled for the mid-2030s. The X-ray Integral Field Unit (X-IFU) represents one of the two instrumental components within the payload, functioning as a cryogenic spectrometer with a spectral resolution of about 4 eV at 7 keV. In this configuration, the CryoAC serves to mitigate the impact of cosmic ray-induced events on the spectrometer TES detectors, which compromises the sensitivity of X-ray measurements. The detector aims to identify and veto non-X-ray events, allowing measurement of faint or distant X-ray sources that will be submerged by background events.In particular, we will present the design and first experimental results of a new CryoAC sample, namely DM#144, developed on the basis of the experience gained with the last CryoAC prototypes. It is a possible candidate for the CryoAC DM1.1, the model to be tested in the future X-IFU FPA Demontration Model 1.1 campaign.Our goal is to provide a comprehensive overview of the current status of the CryoAC for the Athena X-IFU TES detector, offering valuable insights into the ongoing development an design changes of the detector.