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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.
The X-ray telescope of eROSITA will consist of 7 identical and co-aligned mirror modules, each with 54 nested Wolter-1 mirror shells. The mirror shells are glued onto a spider wheel which is screwed to the mirror interface structure making a rigid mechanical unit. The assembly of 7 modules forms a compact hexagonal configuration with 1300 mm diameter (see Fig. 1) and will be attached to the telescope structure which connects to the 7 separate CCD cameras in the focal planes. The co-alignment of the mirror module enables eROSITA to perform also pointed observations.
The replication process described in chapter III allows the manufacturing in one single piece and at the same time of both the parabola and hyperbola parts of the Wolter 1 mirror.
The X-ray telescope of eROSITA will consist of 7 identical and co-aligned mirror modules, each with 54 nested Wolter-1 mirror shells. The mirror shells are glued onto a spider wheel which is screwed to the mirror interface structure making a rigid mechanical unit. The assembly of 7 modules forms a compact hexagonal configuration with 1300 mm diameter (see Fig. 1) and will be attached to the telescope structure which connects to the 7 separate CCD cameras in the focal planes. The co-alignment of the mirror module enables eROSITA to perform also pointed observations.
The replication process described in chapter III allows the manufacturing in one single piece and at the same time of both the parabola and hyperbola parts of the Wolter 1 mirror.
In November 2013, the theme of “The Hot and Energetic Universe” was rated as of highest importance for future exploration and in June 2014 the ATHENA Advanced Telescope for High Energy Astrophysics was selected by ESA for the second large science mission (L2) in the ESA Cosmic Vision program, with launch foreseen in 2028 [4]. By combining a large X-ray telescope with state-of-the-art scientific instruments, ATHENA will address key questions in astrophysics, including: How and why does ordinary matter assemble into the galaxies and galactic clusters that we see today? How do black holes grow and influence their surroundings?
In order to answer these questions, ATHENA needs a powerful mirror system which exceed the capabilities of current missions, especially in terms of collecting area. However, current technologies have reached the mass limits of the launching rocket, creating the need for more light-weight mirror systems in order to enhance the effective area without increasing the telescope mass. Hence new mirror technologies are being developed which aim for low-weight systems with large collecting areas. Light material like glass can be used, which are shaped to form an X-ray reflecting system via the method of thermal glass slumping.
The development and calibration of eROSITA mirror modules is supported by continuous measurements at the X-ray test facility PANTER. To obtain comparable measurement results after each new integration robust alignment procedures are needed to place the mirror module on the optical axis.
Here we present the different methods that we use to align eROSITA like mirror modules. One method uses the symmetry of single reflection images, another one is based on a symmetry of the intensity distribution, and the last one on the symmetry of the half energy width (HEW).
MPE will provide the X-ray Survey Telescope eROSITA for the Russian Spektrum-Roentgen-Gamma Mission. The mirror system consists of a compact bundle of seven co-aligned mirror modules with a focal length of 1600 mm and 54 nested mirror shells each. The 61 arcmin field-of-view (FoV) will yield a high grasp of about 1000 cm2deg2 around 1 keV. An angular resolution of 15 arcsec HEW on-axis (resulting in an average angular resolution of ~26 arcsec HEW over the field-of-view and ~30 arcsec including all optical and spacecraft error contributions) will help distinguish point sources from extended emission of galaxy clusters which are relevant for cosmological studies. During a four year allsky survey eROSITA will generate a new rich database of X-ray sources. In a second phase of the mission eROSITA will also perform pointed observations.
After a mirror development program the integration of flight mirror modules started in early 2011. Currently, the manufacturing of flight modules is ongoing and some of the partially integrated ones have already been X-ray tested. Calibration of completed mirror modules will start end of 2012. Parallel to the X-ray mirrors we have developed an X-ray baffle to suppress stray light from single reflections. It consists of precisely shaped and welded concentric Invar foils which will be mounted on top of each mirror module and aligned by optical means.
We report on the design and the mirror development program including the X-ray baffle and present the latest results from X-ray measurements.
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