Design and development of the follow-up X-ray telescope onboard Einstein Probe in China: a review

Background: The Einstein Probe mission is an astronomical satellite developed in China, focusing on time-domain astronomy in the soft X-ray energy band. A key payload of this mission is the follow-up X-ray telescope (FXT), which is the result of international collaboration between China and Europe. The FXT features gold-coated nickel Wolter-I-type focusing mirrors and utilizes PNCCD detectors for imaging and spectroscopy in the focal plane.
Methods: We reviewed the seven-year development history of the FXT. Initially, the configuration of the FXT consisted of a single telescope unit in 2017, but it later evolved into a dual-unit setup. Building on the successful design of eROSITA, the FXT team has innovatively introduced new operational modes for the PNCCD. FXT team also developed an ultra-compact helium pulse tube refrigerator, which cools the PNCCD down to -90℃. Additionally, various passive shielding measures have been implemented to protect against high-energy charged particles and enhance radiation resistance. These advancements have significantly improved the overall performance and reliability of the FXT.
Results and conclusion: The ground calibrations and tests of the FXT demonstrate that its primary performance meets the established design goals. The FXT has exhibited outstanding performance in orbit, establishing itself as one of the space X-ray telescopes with considerable international influence.