Follow-up x-ray telescope (FXT) mirror module for the Einstein Probe mission

The Einstein Probe (EP) is a mission of the Chinese Academy of Sciences (CAS) dedicated to time-domain high-energy astrophysics. Its primary goals are to discover high-energy transients and monitor variable objects. The ESA Science Programme Committee (SPC) approved on 19 June 2018 the participation of ESA to the CAS EP mission as a Mission of Opportunity. Among other elements, CAS has requested ESA participation for the provision of the Mirror Modules of the Follow-Up X-ray Telescope (FXT). FXT is a pair of Wolter-I telescopes operating in the 0.5-10 keV energy range, inheriting the design from eROSITA [2][3]. It provides field of view of about 1 deg diameter. The source localization error will be of 5-15 arcsec depending on the source strength [1]. The FXT is responsible for the quick follow-up observations of the triggered sources and will also observe other interested targets during the all-sky survey at the rest time. Three FXT Mirror Modules were produced: Structural and Thermal Model (STM), Qualification Model (QM) and Flight Model (FM). Media Lario could leverage on the manufacturing and integration infrastructure still available at its premises from the eROSITA programme [3][4], including the complete set of 54 mandrels needed for the mirror repliforming, property of MPE. Media Lario produced and integrated the FXT Mirror Modules, each comprising 54 nested repliformed mirror shells; Max-Planck Institute (MPE) conducted the X-ray optical tests at the PANTER facility, for the acceptance of all the different models. This efficient collaboration enabled the on-time and in-quality delivery of the FXT Mirror Modules.