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Abstract:
The Wide Field Imager (WFI) instrument for ESA’s next large X-ray mission Athena is designed for imaging and spectroscopy over a large field of view, and high count rate observations up to and beyond 1 Crab source intensity. The other focal plane instrument, the cryogenic X-IFU camera, is designed for high-spectral resolution imaging. Both cameras share alternately a mirror system based on silicon pore optics with a focal length of 12 m and unprecedented large effective area of about 1.4 m2 at 1keV. The WFI instrument employs DEPFET active pixel sensors, which are fully depleted, back-illuminated silicon devices of 450 μm thickness. The detectors provide high quantum efficiency and state-of-the art energy resolution in the 0.2 keV to 15 keV energy range with extremely fast readout speeds compared to previous generations of Si detectors for X-ray astronomy. The focal plane comprises a Large Detector Array (LDA) and a Fast Detector (FD). The LDA comprises about 1 million pixels and a time resolution in full frame mode of 5 ms. The FD optimized for bright point source observations permits a time resolution of even 80 μs with about 4000 pixels. Both detectors have a pixel size of 130 μm × 130 μm, providing oversampling of the PSF by a factor >2. The instrument development is in phase B of the project after a successful Preliminary Requirements Review and endorsement of the both instrument consortia by ESA. Critical technology developments for the WFI focal plane camera are currently investigated and finally experimentally verified with breadboard models: the detector function and performance, the real-time capability of onboard event pre-processing and the integrity of the large-area and ultra-thin optical blocking filter after environmental tests. Flight-size sensors have been produced and a flight-like detector assembly has been developed. First test results of a flight-size detector are expected in near future. Based on the thermal design and model for the camera head (CH), thermal interface requirements have been estimated.
