We report on results of the on-ground X-ray calibration of the Wide-field X-ray Telescope (WXT), built from novel lobster-eye micro-pore optics, on board the Einstein Probe (EP) satellite. To fully characterize the performance and properties of the WXT instrument, a series of tests and calibrations were conducted at different levels of devices, assemblies and the complete module before the launch of EP. In this paper, we present the calibration results of three flight model modules (FM1, FM5 and FM11) obtained during their end-to-end module calibration experiments carried out at the 100-m X-ray Test Facility (100XF) of the Institute of High Energy Physics (IHEP), Chinese Academy of Sciences (CAS). Measurements of the Point Spread Function (PSF), effective area, and energy response were performed for multiple incident directions and several characteristic X-ray emission line energies. Specifically, the distributions of the PSF and effective areas are found to be roughly uniform across the FoV, in large agreement with the prediction of lobster-eye optics. Their energy-dependent behavior aligns well with theoretical predictions and Monte Carlo simulations. At ∼ 1.25 keV, the full width at half maximum (FWHM) of the focal spot ranges from 3-7 arcmin (with a median of ∼ 4.2 arcmin) and the effective area is in range of ∼ 2-3 cm^2 . Noticeably, the flight model instruments demonstrate a ∼ 1.5 arcmin improvement in spatial resolution over the previously launched Lobster Eye Imager for Astronomy. The properties of the complementary metal-oxide semiconductor (CMOS) sensors were also calibrated. The gain coefficients are in range of 6.4-6.9 eV/DN . The energy resolutions are in range of ∼ 120 to 140 eV at 1.25 keV, meeting design requirements. These calibration results have been ingested into the first version of calibration database (CALDB) and applied to the analysis of the scientific data acquired by WXT after the launch of EP.

The Einstein Probe (EP) mission, launched in 2024 January, is a time-domain X-ray satellite designed to discover and study X-ray transient and burst sources while investigating electromagnetic counterparts to gravitational waves. To achieve precise observations, EP features the Follow-up X-ray Telescope (FXT), equipped with two Wolter-I type mirrors for precise imaging within a 1 square degree field of view. A specialized Ray-Tracing package for the FXT (RTF) was developed to assess the Wolter-I type mirrors’ performance used in FXT. By employing specialized algorithms to simulate X-ray photon total reflection, RTF has yielded valuable insights into key optical parameters such as point-spread function, effective area, and vignetting. The package also evaluates components like the X-ray baffle and filter wheel, further enhancing the optical system’s efficacy. Moreover, the ray-tracing results have been validated against measurements. These simulations are crucial for ground calibration and will assist in maximizing the scientific output of the EP mission by improving the understanding of mirrors’ behavior in various observational conditions.

The Einstein Probe (EP) is an X-ray astronomical satellite designed for time-domain astronomy. The Follow-up X-ray Telescope (FXT) is an important payload on the EP. The FXT’s detector utilizes a pn-junction charge-coupled device (pnCCD), which is currently the fastest-readout X-ray CCD worldwide. The design and implementation of a dedicated power-supply and monitoring module constitute a key aspect in the development of the detector system. The FXT comprises several components, including the electric control box (EC-Box), the detector electronics box (DE-Box), and the focusing camera. The detector module of the focusing camera consists of two primary components: the pnCCD and the multi-channel analog signal processing chip known as the CAMEX (CMOS amplifier and multiplexer) ASIC. The CAMEX ASIC is used for the readout of the pnCCD signals. The operation of the detector module requires a sophisticated power-supply module. This paper details the design and implementation of a dedicated power-supply and monitoring module for the detector module. Based on the voltage requirements of the detector module, the power-supply module has been designed to include switchable, adjustable, and programmable functions. The monitoring module includes voltage, current, and temperature monitoring based on the different types of monitoring. The power-supply and monitoring module operates reliably and performs effectively in orbit, meeting the requirements of the FXT payload on the EP satellite. The power-supply and monitoring module has successfully provided a stable power-supply and monitoring module for the detector module. It operates effectively in orbit, ensuring that the detector system achieves optimal performance.

In this paper we present the current status of the enhanced X-ray Timing and Polarimetry mission, which has been fully approved for launch in 2030. eXTP is a space science mission designed to study fundamental physics under extreme conditions of matter density, gravity, and magnetism. The mission aims at determining the equation of state of matter at supra-nuclear density, measuring the effects of quantum electro-dynamics, and understanding the dynamics of matter in strong-field gravity. In addition to investigating fundamental physics, the eXTP mission is poised to become a leading observatory for time-domain and multi-messenger astronomy in the 2030's, as well as providing observations of unprecedented quality on a variety of galactic and extragalactic objects. After briefly introducing the history and a summary of the scientific objectives of the eXTP mission, this paper presents a comprehensive overview of: 1) the cutting-edge technology, technical specifications, and anticipated performance of the mission's scientific instruments; 2) the full mission profile, encompassing spacecraft design, operational capabilities, and ground segment infrastructure.

The first pathfinder of the CATCH mission, CATCH-1, was launched in June 2024. It is equipped with a light-weight, narrow-field optimized Lobster Eye X-ray Optics. By sacrificing a portion of the field of view to achieve a large effective area, the telescope’s sensitivity is enhanced. This paper presents the equipment and procedures employed for calibrating the optics assembly. A comprehensive on-ground calibration for the Lobster Eye X-ray Optics is conducted before its launch using multi-target X-ray sources and the pnCCD Color X-Ray Camera in the 100 m X-Ray Test Facility. The results are derived from calibration measurements taken before and after the mechanical testing and mainly include measurements of the focal length, point spread function, angular resolution, and the effective area for incident X-rays at 0.28 keV, 0.93 keV, 1.49 keV, 2.98 keV, and 4.51 keV. The results indicate that the mirror’s performance remains stable and no observable variation before and after the mechanical testing. At 0.93 keV, the mirror’s angular resolution is 6.11^' (FWHM), and the effective area is 40.75 cm^2 , meeting the expected performance of CATCH-1 X-ray optics.

The follow-up X-ray telescope (FXT) is one of the two payloads of the Einstein Probe (EP), consisting of the upper composite with the X-ray mirror module as the core, the lower composite with the pnCCD module as the core, and the interface structure. The FXT thermal control subsystem is responsible for the thermal design, thermal implementations, and testing of the entire FXT payload thermal control. A design approach is adopted with passive thermal control technology as the main method and active thermal control technology as a supplement for common components. The X-ray mirror modules are high-precision optical components, utilizing active closed-loop temperature control to ensure high precision and stability. The pnCCD detectors operate at a stable low temperature, with refrigerators used to cool the detector houses, ensuring they can operate under stable low-temperature conditions. The hot ends of the refrigerators are connected to the external radiator panels through heat pipes for heat dissipation. The thermal control subsystem of FXT is operating properly in-orbit. All component temperatures meet the design requirements. After multiple rounds of design and test verification, FXT was successfully launched with EP and completed in-orbit testing. During the in-orbit testing phase of EP, the function of the FXT thermal control subsystem works well. The temperatures of the components and units are normal. This paper introduces the design of FXT thermal control and the in-orbit performance of the thermal control subsystem.

Mini-magnets of FXT are designed to deflect low-energy electrons that are incident into the camera aperture area, preventing them from reaching the focal plane detector and thereby reducing the noises they generate. By employing a combination of theoretical calculations and experimental measurements, the parameters of the FXT mini-magnets were obtained, including magnetic field distributions, magnetic moment results, and electron deflection efficiency. The structural and magnetic models of the optimized mini-magnets are presented. Distributions of magnetic field intensity on different planes within the camera aperture are compared with the measured results from the FXT flight models (FMs). The results for the total and separated magnetic moment of two sets of FMs are also provided. Additionally, the deflection efficiency for 25 keV electrons is calculated under various incident conditions. The FMs of mini-magnets show good performance, with the measured values of magnetic field distributions being highly consistent with the theoretical values. A perfect result for total magnetic moment of less than 10 mA·m^2 has been achieved, far better than requirement of 100 mA·m^2 . The calculated electron deflection efficiency reached over 99.88

In order to evaluate the mechanical feasibility of the domestic baffle made by wire electrode cutting for the mirror assembly of the Follow-up X-ray Telescope (FXT) onboard the Einstein Probe (EP) mission. Finite element analysis was performed to compare the structural differences between the domestic baffle made by wire electrode cutting and the eROSITA baffle made by bonding. The finite element models were verified by test data in advance to avoid significant deviations. Finally, the differences in dynamical performances between the FXT mirror assemblies with the two baffles were investigated through modal analysis and frequency response analysis using the pre-verified models. The results show that, from the perspective of the entire mirror assembly, their eigenfrequencies remain similar, except for the second lateral eigenfrequency, which shifts forward by approximately 24 Hz in the mirror assembly equipped with the domestic baffle. However, for the X-ray baffles themselves, the axial and lateral eigenfrequencies of the two baffles differ by approximately 49 Hz and 185 Hz, respectively. These eigenfrequencies are staggered, ensuring that over-response is avoided. In terms of response amplification, the domestic baffle, compared to the eROSITA baffle, exhibits inferior axial mechanical characteristics but superior lateral characteristics. In summary, from a mechanical perspective, the domestic baffle is feasible.

The Einstein Probe (EP) satellite is a space X-ray satellite for time-domain astronomy and high-energy astrophysics. The precision control of the optical structure directly affects the imaging quality and positioning accuracy of the Follow-up X-ray Telescope (FXT), playing a crucial role in achieving the on-orbit scientific objectives of the FXT. Higher positioning accuracy makes it easier to identify corresponding bodies for the discovery and positioning of transient sources. Accurate positioning is beneficial for follow-up observations in other bands, such as optical spectroscopy. This article mainly introduces the precision control methods and processes of the FXT optical structure, which have been tested and verified through satellite test. The on-orbit source positioning accuracy of the FXT telescope is within 20 arcseconds (90 ^' ^' at 68

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. 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 ^∘ C. 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. 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.

The Einstein probe (EP) is an X-ray astronomical satellite dedicated to time-domain astronomy and high-energy astrophysics. Initiated at the end of 2017, it was successfully launched on January 9, 2024. The follow-up X-ray telescope (FXT) is a key payload on the EP satellite. The FXT employs PNCCD as its focal plane detector. Its electronic components include the electronic control box (EC-Box), the detector electronics boxes (DE-Box), the refrigerator controller, the movement mechanisms controller, and the temperature control instrument. The FXT conducted functional performance tests in-orbit as planned, including three operating modes of the detector, energy detection range, and energy resolution. Since FXT became operational in orbit, all electronic equipment has been working stably. The FXT has an energy detection range of 0.3–10 keV, with an energy resolution of approximately 92 eV @ 1.25 keV, and an electronic noise of about 3.3 e^- .

The Follow-up X-ray Telescope (FXT) is one of the main scientific instruments on board the Einstein Probe astronomical satellite, which was launched in 2024 January. FXT consists of two Wolter I type nested telescopes (FXT-A and FXT-B) with a focal length of 1600 mm. The focal plane detector employs a PNCCD with 384 x 384 pixels. The timing mode of FXT serves as the primary operating mode for fast X-ray timing observations. To evaluate and validate the timing performance of FXT prior to launch, a comprehensive timing calibration was performed at the 100 m X-ray test facility. By simulating various periodic Crab-like profiles using the Grid Controlled X-ray Tube (GCXT) in conjunction with a pulsar simulation module, it was verified that the relative time accuracy of FXT exceeds 5 x 10(-9). Furthermore, employing GCXT with a voltage pulse generation module enabled the determination of the time resolutions for FXT-A and FXT-B, recorded as 45.6 +/- 2.7 mu s and 47.1 +/- 2.8 mu s, respectively. An absolute timing calibration for FXT-B was carried out using the GCXT and a time interval analyzer, revealing a measured time delay of 3.9 +/- 2.1 mu s for FXT-B.

The Follow-up X-ray Telescope (FXT) is one of the two main scientific instruments on board the Einstein Probe astronomical satellite, which was launched in 2024 January. FXT focuses on the energy range of 0.3-10 keV and mainly conducts follow-up observations of transients and burst sources. It consists of two units of completely independent optical system and detector system (FXT-A and FXT-B). The focal plane detector adopts PNCCD provided by Max Planck Institute for Extraterrestrial Physics. FXT was designed to have three operating modes with different integration times and readout schemes, namely full-frame mode, partial-window mode and timing mode. We conducted a detailed calibration for PNCCD at the Institute of High Energy Physics before launch. Our results demonstrate that both FXT-A and FXT-B exhibit excellent spectral performance. The energy resolution (Full Width at Half Maximum) of FXT-A and FXT-B are both better than 85 eV at 1.487 keV. We determined a mean equivalent noise charge around 2.8 e- for FXT-A and FXT-B in three operating modes at -90 degrees C +/- 0.5 degrees C, except for a few noisy pixels in full-frame mode. In addition, we measured the relation of charge transfer inefficiency as function of photon energy and confirmed the ability to detect photons in the energy range of 0.3-10 keV. These calibration results have been ingested into the initial version of calibration database and applied to the analysis of scientific data acquired by FXT.

The Chasing All Transients Constellation Hunters (CATCH) space mission is an intelligent constellation consisting of 126 micro-satellites in three types (A, B, and C), designed for X-ray observation with the objective of studying the dynamic universe. Currently, we are actively developing the first Pathfinder (CATCH-1) for the CATCH mission, specifically for type-A satellites. CATCH-1 is equipped with Micro Pore Optics (MPO) and a 4-pixel Silicon Drift Detector (SDD) array. To assess its scientific performance, including the effective area of the optical system, on-orbit background, and telescope sensitivity, we employ the Monte Carlo software Geant4 for simulation in this study. The MPO optics exhibit an effective area of $41$ cm$^2$ at the focal spot for 1 keV X-rays, while the entire telescope system achieves an effective area of $29$ cm$^2$ at 1 keV when taking into account the SDD detector's detection efficiency. The primary contribution to the background is found to be from the Cosmic X-ray Background. Assuming a 625 km orbit with an inclination of $29^\circ$, the total background for CATCH-1 is estimated to be $8.13\times10^{-2}$ counts s$^{-1}$ in the energy range of 0.5--4 keV. Based on the background within the central detector and assuming a Crab-like source spectrum, the estimated ideal sensitivity could achieve $1.9\times10^{-12}$ erg cm$^{-2}$ s$^{-1}$ for an exposure of 10$^4$ s in the energy band of 0.5--4 keV. Furthermore, after simulating the background caused by low-energy charged particles near the geomagnetic equator, we have determined that there is no need to install a magnetic deflector.

CATCH-1, as the first satellite of Chasing All Transients Constellation Hunters (CATCH) space mission, was successfully launched into its expected orbit on June 22, 2024. The flight model underwent environmental tests before launch, including thermal cycling, thermal vacuum, and mechanical evaluations. The CATCH-1 detector system is equipped with a 4-pixel Silicon Drift Detector (SDD) array. To ensure the reliability and redundancy of the CATCH-1 detector system, two sets of data acquisition systems were independently designed and calibrated. Our focus is on presenting the ground calibration results of CATCH-1, which demonstrate a strong linear correlation between energy and channel. The main data acquisition system achieves an energy resolution of ∼ 120 eV@4 keV, while the backup data acquisition system has a slightly lower energy resolution of around 150 eV@4 keV, both meeting the design requirement of ≤ 160 eV@4 keV. Additionally, the time resolution is ∼ 4 μ s , complying with the design requirement of ≤ 10 μ s . The calibration database now includes the ground calibration results of CATCH-1, establishing a dependable basis for future data analysis. The development experience, calibration, and test results of this detector system will also provide a solid foundation for subsequent tasks such as CATCH-2.

Reflectivity is a key topic in soft X-ray optics research and serves as the foundation for studying the performance of the optics for X-ray astronomical satellites. Since its establishment, the 100-m X-ray Test Facility (100XF) has been continuously developing various testing functionalities, including calibration of timing, imaging, and energy response. This paper provides a detailed description of the X-ray optics reflectivity test method based on the 100XF, which can be applied to various grazing incident X-ray optics, including Wolter-I and lobster-eye types, significantly expanding the application scope of the 100XF. A flat mirror sample (SiO _2 coated on a Si wafer) is tested. Results of the variation of reflectivity with angle @ C-K α (0.28 keV), Al-K α (1.49 keV), and Ti-K α (4.50 keV) are presented in the description. The reflectivity test method has also been applied to the coating reflectivity study of the enhanced X-ray Timing and Polarimetry Mission (eXTP) mirror. At the same time, a new method utilizing the continuum spectrum of bremsstrahlung was carried out to study the continuous variation of reflectivity with energy, greatly improving efficiency compared to traditional methods, and all the results show a good agreement with the theoretical values. The deviation between the test and theoretical values in the low-energy range (1.5-8.0 keV) is less than 10

Reflectance is a key topic in soft X-ray optics research and serves as the foundation for the study of X-ray astronomical satellites and payload performance. Since its establishment, the 100-m X-ray Test Facility (100XF) has been continuously developing various testing functionalities, including calibration of timing, imaging, and energy response. This paper provides a detailed description of the X-ray optics reflectance test method based on the 100XF, which is applicable to various grazing incident X-ray optics, including Wolter-I and lobster-eye types, significantly expanding the application scope of the 100XF. A flat mirror sample (SiO2 coated on Si wafer) are tested. Results of the variation of reflectivity with angle @ C-Kα (0.28 keV), Al-Kα(1.49 keV) and Ti-Kα(4.50 keV) are presented among the description. Additionally, reflectance test method has been applied to the coating reflectivity study of the enhanced X-ray Timing and Polarimetry Mission (eXTP) mirror. At the same time, a new method utilizing continuum spectrum of bremsstrahlung was carried out for studying the continuous variation of reflectivity with energy, greatly improving efficiency compared to traditional methods, and all the results show a good agreement with the theoretical values. The deviation between the test values and theoretical values in the low-energy range (1.5-8.0 keV) is less than 10%.

The Follow-up X-ray telescope (FXT) is one of the instruments on board the Einstein Probe (EP) satellite of the Chinese Academy of Sciences (CAS) which was launched in January 2024. The EP mission is dedicated to the study of time-domain high-energy astrophysics, utilising a lobster-eye-based wide-field telescope, complemented by an eROSITA-like optics for follow-up observations. MPE has provided hardware and conducted measurement campaigns at its test facilities as part of a European contribution to Einstein Probe by ESA, and in addition the eROSITA flight spare mirror assembly as the second FXT module. Three FXT mirror assemblies – structural-thermal, qualification and flight models – have been manufactured. All components underwent acceptance testing using X-rays, followed by the installation of X-ray baffles for stray-light rejection. Subsequently, they underwent environmental tests and X-ray performance evaluations. The final tests of the qualification model, serving as a flight spare, and the flight model included an X-ray calibration at various photon energies ranging from about 0.3keV to 8keV. All tests were performed at MPE’s test facilities: the laboratory for vibration and thermal-vacuum testing, and the PANTER X-ray facility. Reported are the setups and the results of the respective test sequences, focusing on the qualification and flight mirror assemblies. After delivery to China, all mirror assemblies were subjected to complementary measurements in the X-ray test facility of the Institute for High Energy Physics (IHEP) of CAS.