X-ray testing of the Einstein Probe follow-up x-ray telescope STM at MPE’s PANTER facility

The Einstein Probe mission, due to launch in late 2022, will study time-domain astrophysics and monitor variable objects. It aims to observe x-ray counterparts of gravitational wave sources and high-redshift gamma ray bursts. Developed and built by the Chinese Academy of Sciences, Einstein Probe will use two types of telescope: the WideField X-ray Telescope (WXT) and the Follow-Up X-ray Telescope (FXT). The FXT will perform follow-up observations of sources discovered by the WXT, and will observe in the energy range of 0.5 to 8 keV. The performance aim of the FXT – the point spread function half-energy width (PSF HEW) – is <20 arcseconds (on-axis at 1.49 keV). The Max-Planck Institute for Extraterrestrial Physics (MPE) is producing and integrating the x-ray straylight baffle for the FXT, as well as testing and calibrating the different models of the FXT x-ray optic. Production of the structural-thermal model (STM) for Einstein Probe FXT began in 2019. The STM mirror module, produced by Media Lario, has been tested at MPE’s PANTER x-ray test facility. Following this acceptance test, further x-ray tests have been performed at PANTER after each of the subsequent stages: the mounting of the x-ray baffle, the shock and vibration test, and the thermal cycling test. The x-ray performance of the FXT STM is documented at each stage and the results of each test are presented in this paper.