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The Wide Field Imager for the Athena X-ray telescope is composed of two back side illuminated detectors using DEPFET sensors operated in rolling shutter readout mode: A large detector array featuring four sensors with 512x512 pixels each and a small detector that facilitates the high count rate capability of the WFI for the investigation of bright, point-like sources. Both sensors were fabricated in full size featuring the pixel layout, fabrication technology and readout mode chosen in a preceding prototyping phase. We present the spectroscopic performance of these flight-like detectors for different photon energies in the relevant part of the targeted energy range from 0.2 keV to 15 keV with respect to the timing requirements of the instrument. For 5.9 keV photons generated by an iron-55 source the spectral performance expressed as Full Width at Half Maximum of the emission peak in the spectrum is 126.0 eV for the Large Detector and 129.1 eV for the Fast Detector. A preliminary analysis of the camera's signal chain also allows for a first prediction of the performance in space at the end of the nominal operation phase., Comment: SPIE Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray

The Spectrum-Roentgen-Gamma satellite with the extended roentgen survey with an imaging telescope array (eROSITA) x-ray telescope as scientific payload was successfully launched on July 13, 2019 and deployed in a 6-month halo orbit around the second Lagrange point of the Sun–Earth system. The telescope comprises an array of seven mirror systems with seven focal plane cameras. The spectroscopic CCD cameras are a further development of the very successful EPIC-PN camera on the XMM-Newton satellite, which is still operating after more than 20 years in space. The key component of the camera is the detector, which matches the large field of view of 1 deg to permit an all-sky survey in the energy range from 0.2 to 8 keV with state-of-the-art energy resolution. The image area of the PN-junction charge coupled device comprises 384 × 384 pixels. The pixel size of 75 × 75 μm2 each matches the angular resolution of the mirror system. Readout of the full frame is achieved in 9.18 ms but for thermal and onboard event preprocessing reasons, the time resolution is slowed down to 50 ms. The photon entrance window of five of the seven CCDs is equipped with an optical blocking filter, which proved to be advantageous. The improved concept and design of the eROSITA cameras will be explained as well as their operation and performance in space.

eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the primary instrument on the Spectrum-Roentgen-Gamma (SRG) mission, which was successfully launched on July 13, 2019, from the Baikonour cosmodrome. After the commissioning of the instrument and a subsequent calibration and performance verification phase, eROSITA started a survey of the entire sky on December 13, 2019. By the end of 2023, eight complete scans of the celestial sphere will have been performed, each lasting six months. At the end of this program, the eROSITA all-sky survey in the soft X-ray band (0.2--2.3\,keV) will be about 25 times more sensitive than the ROSAT All-Sky Survey, while in the hard band (2.3--8\,keV) it will provide the first ever true imaging survey of the sky. The eROSITA design driving science is the detection of large samples of galaxy clusters up to redshifts $z>1$ in order to study the large-scale structure of the universe and test cosmological models including Dark Energy. In addition, eROSITA is expected to yield a sample of a few million AGNs, including obscured objects, revolutionizing our view of the evolution of supermassive black holes. The survey will also provide new insights into a wide range of astrophysical phenomena, including X-ray binaries, active stars, and diffuse emission within the Galaxy. Results from early observations, some of which are presented here, confirm that the performance of the instrument is able to fulfil its scientific promise. With this paper, we aim to give a concise description of the instrument, its performance as measured on ground, its operation in space, and also the first results from in-orbit measurements., 16 pages, 19 figures, accepted by Astronomy & Astrophysics

The SRG satellite with the eROSITA X-ray telescope as scientific payload was successfully launched on July 13, 2019 and deployed in a 6-month halo orbit around the second Lagrange point of the Sun Earth system. The telescope comprises an array of seven mirror systems with seven focal plane cameras. The spectroscopic CCD cameras are a further development of the very successful EPIC PN camera on the XMM-Newton satellite, which is after 20 years in space still successfully operating. Key component of the camera is the detector, which matches the large field of view of 1° to permit an all-sky survey in the energy range from 0.2 keV to 8 keV with state-of-the-art energy resolution. The image area of the PNCCD comprises 384 x 384 pixels. Their size of 75 x 75 μm2 each, matches the angular resolution of the mirror system. Readout of the full frame is achieved in 9.18 ms but for thermal and onboard event pre-processing reasons, the time resolution is slowed down to 50 ms. The photon entrance window of five of the seven CCDs is equipped with an optical blocking filter, which turned out to be advantageous. The improved concept and design of the eROSITA cameras will be explained as well as their operation and performance in space.

The power of eROSITA (extended ROentgen Survey with an Imaging Telescope Array), the core instrument on the Russian–German Spectrum–Roentgen–Gamma (SRG) mission, is high sensitivity at high spectral, spatial, and temporal resolution over a large field of view. This is achieved by combining 7 coaligned X–ray telescope modules, each composed of 54 paraboloid / hyperboloid mirror shells in a Wolter–I geometry, to focus the X–rays through optical blocking filters onto PNCCDs with a total of 1 million pixels, providing a spectral resolution of 60 – 160 eV FWHM over an energy range 0.2 – 8 keV and a 1 degree field of view at a time resolution of 50 ms. In order to make full scientific use of the unique capabilities of eROSITA, all the individual components have to be calibrated. The initial ground calibration was done at the PANTER and PUMA facilities of MPE as well as at BESSY, and was supplemented by an in–orbit calibration. We report on the extensive and often challenging calibration activities performed on ground and in space.

The Wide Field Imager (WFI), one of two complementary instruments on board ESA's next large X-ray mission Athena, combines state-of-the-art resolution spectroscopy with a large field of view and high count rate capability. Centerpiece of the WFI instrument are four DEPFET (Depleted p-channel field effect transistor) sensors with a size of 512_512 pixels each and one fast detector with a size of 64_64 pixels. They are planned to be operated in drain current readout mode, which enables fast readout rates but is sensitive to inhomogeneities of the drain currents. These inhomogeneities arise from the sheer size of the DEPFET sensor matrix and are originated in the spatial distribution of wafer properties and process parameters. We characterized the drain current distribution of a prototype device (64_64 pixels) utilizing the same layout and technology as specified for the pre-flight production of Athena's WFI DEPFET detectors. In order to better understand the origin of the current spread we measured I-V characteristics of all pixels and extracted threshold voltages and transconductance values of the detector in operational conditions. This is enabled by features of the VERITAS read-out ASIC.

The Wide Field Imager (WFI) instrument is one of two complementary focal plane cameras on ESA’s next large class X-ray astronomy mission Athena. It is coupled to a high performance X-ray mirror to provide an unprecedented survey power by combining a large field of view with an excellent count rate capability. The required spectral performance, sensitive area and readout timing necessitated the development of specific DEFPET detectors. In the course of the technology development phase of the project, different options of prototype detectors were fabricated and investigated. As a result, a new generation of spectroscopic X-ray DEPFET detectors was developed for the flight production. Those detectors will feature a linear gate layout, thin gate oxide fabrication technology and a drain current readout. In this paper, we present the detailed characterization of a prototype detector covering a large sensitive area of 256 × 256 pixels. Due to the progress in the detector development an energy resolution as low as 128 eV FWHM at 6 keV was obtained.

The Wide Field Imager instrument of ESA’s next X-ray observatory Athena will consist of specifically developed DEPFET detectors which enable a low noise and fast readout operation. In order to confirm the required spectroscopic performance within the energy range of 0.2 keV to 15 keV, various emission lines were probed with prototype detectors on a 64×64 pixel scale. These detectors include the first sensors representative for flight with respect to the transistor layout and fabrication technology. Four different detectors were tested and exhibit a Fano noise limited spectral performance. The required energy resolution was achieved by all detectors even at readout times as fast as 2.5 μs/row. Additionally, one of the detectors achieved an outstanding performance of a FWHM below 45 eV at C Kα (277 eV) and 6.1 μs/row. Complementary to the measurements, the charge cloud size was determined as a function of the photon energy based on Monte Carlo simulations. These simulations enable a quantification of the effective charge loss at different energies due to the thresholds applied at the event recombination.

The Wide Field Imager (WFI) is one of two instruments for ESA’s Athena X-ray observatory. It will employ DEPFET (depleted p-channel field effect transistor) active pixel technology to provide unprecedented spectroscopic and imaging capabilities over a broad energy band from 0.2 keV to 15 keV, with a large field of view of 40′ × 40′ . Using prototype detectors of various sizes we have started first tests of window mode operation, where only a subset of the full sensor array is being read out, leading to a higher frame rate for this area. We also investigated the possibility of operation at room temperature for a basic functionality test when cooling is not possible, e.g. on ground after integration on the satellite.

The Wide Field Imager (WFI), one of two complementary instruments on board ESA’s next large X-ray mission Athena, combines state-of-the-art resolution spectroscopy with a large field of view and high count rate capability. Centerpiece of the WFI instrument are four DEPFET (Depleted p-channel FET) detectors with a size of 512×512 pixels each. Their size involves challenging demands on the readout process, concerning timing and homogeneity over such large scales. In order to estimate the influence of flight size, smaller prototype sensors of various size, chosen to address the specific problems, were produced and characterized. Both possible readout modes, source follower and drain current readout, were investigated regarding their specific size dependent problems. Time resolution of the particularly stable source follower readout is limited by RC time constants and the fast drain current mode is restricted by inhomogeneities of the pixel matrix, demanding specific properties of the Veritas readout ASIC. To characterize these effects, spectroscopic measurements, showing good performance of the devices, were complemented with electrical ones, enabled by features of the Veritas-ASIC. We characterized the time dependency of the source potential and its influence on signal offset in source follower mode as well as the influence of drain current distribution on detector properties in drain current mode. The limits and capabilities of the current to voltage converter stage were also investigated. Performance measurements on large prototype detectors using photon energies of 5.9 keV show promising results.

Metallic mirrors are foreseen to play a crucial role for all optical diagnostics in ITER. Therefore, the development of reliable techniques for the production of mirrors which are able to maintain their optical properties in the harsh ITER environment is highly important. By applying magnetron sputtering and evaporation techniques, rhodium and molybdenum films have been prepared for tokamak tests. The films were characterised in terms of chemical composition, surface roughness, crystallite structure, reflectivity and adhesion. No impurities were detected on the surface after deposition. The effects of deposition parameters and substrate temperature on the resulting crystallite structure, surface roughness and hence on the reflectivity, were investigated. The films are found to exhibit nanometric crystallites with a dense columnar structure. Open boundaries between the crystallite columns, which are sometimes present after evaporation, are found to reduce the reflectivity as compared to rhodium or molybdenum references.

eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the core instrument on the Russian/German Spektrum-Roentgen-Gamma (SRG) mission which is now officially scheduled for launch on March 26, 2016. eROSITA will perform a deep survey of the entire X-ray sky. In the soft band (0.5-2 keV), it will be about 30 times more sensitive than ROSAT, while in the hard band (2-8 keV) it will provide the first ever true imaging survey of the sky. The design driving science is the detection of large samples of galaxy clusters to redshifts z < 1 in order to study the large scale structure in the universe and test cosmological models including Dark Energy. In addition, eROSITA is expected to yield a sample of a few million AGN, including obscured objects, revolutionizing our view of the evolution of supermassive black holes. The survey will also provide new insights into a wide range of astrophysical phenomena, including X-ray binaries, active stars and diffuse emission within the Galaxy. eROSITA is currently (June 2014) in its flight model and calibration phase. All seven flight mirror modules (+ 1 spare) have been delivered and measured in X-rays. The first camera including the complete electronics has been extensively tested (vacuum + X-rays). A pre-test of the final end-toend test has been performed already. So far, all subsystems and components are well within their expected performances.

The eROSITA space telescope is currently developed for the determination of cosmological parameters and the equation of state of dark energy via evolution of clusters of galaxies. Furthermore, the instrument development was strongly motivated by the intention of a first imaging X-ray all-sky survey enabling measurements above 2 keV. eROSITA is a scientific payload on the Russian research satellite SRG. Its destination after launch is the Lagrangian point L2. The observational program of the observatory divides into an all-sky survey and pointed observations and takes in total about 7.5 years. The instrument comprises an array of 7 identical and parallel aligned telescopes. Each of the seven focal plane cameras is equipped with a PNCCD detector, an enhanced type of the XMM-Newton focal plane detector. This instrumentation permits spectroscopy and imaging of X-rays in the energy band from 0.3 keV to 10 keV with a field of view of 1.0 degree. The camera development is done at the Max-Planck-Institute for extraterrestrial physics. Key component of each camera is the PNCCD chip. This silicon sensor is a back-illuminated, fully depleted and column-parallel type of charge coupled device. The image area of the 450 micron thick frame-transfer CCD comprises an array of 384 x 384 pixels, each with a size of 75 micron x 75 micron. Readout of the signal charge that is generated by an incident X-ray photon in the CCD is accomplished by an ASIC, the so-called eROSITA CAMEX. It provides 128 parallel analog signal processing channels but multiplexes the signals finally to one output which feeds the detector signals to a fast 14-bit ADC. The read noise of this system is equivalent to a noise charge of about 2.5 electrons rms. We achieve an energy resolution close to the theoretical limit given by Fano noise (except for very low energies). For example, the FWHM at an energy of 5.9 keV is approximately 140 eV. The complete camera assembly comprises the camera head with the detector as key component, the electronics for detector operation as well as data acquisition and the filter wheel unit. In addition to the on-chip light blocking filter directly deposited on the photon entrance window of the PNCCD, an external filter can be moved in front of the sensor, which serves also for contamination protection. Furthermore, an on-board calibration source emitting several fluorescence lines is accommodated on the filter wheel mechanism for the purpose of in-orbit calibration. Since the spectroscopic silicon sensors need cooling down to -95°C to mitigate best radiation damage effects, an elaborate cooling system is necessary. It consists of two different types of heat pipes linking the seven detectors to two radiators. Based on the tests with an engineering model, a flight design was developed for the camera and a qualification model has been built. The tests and the performance of this camera is presented in the following. In conclusion an outlook on the flight cameras is given.

The eROSITA space telescope is presently developed for the determination of cosmological parameters and the equation of state of dark energy via evolution of galaxy clusters. It will perform in addition a census of the obscured black hole growth in the Universe. The instrument development was also strongly motivated by the intention of a first imaging X-ray all-sky survey above an energy of 2 keV. eROSITA is scientific payload on the Russian research satellite SRG and the mission duration is scheduled for 7.5 years. The instrument comprises an array of seven identical and parallel-aligned telescopes. The mirror system is of Wolter-I type and the focal plane is equipped with a PNCCD camera for each of the telescopes. This instrumentation permits spectroscopy and imaging of X-rays in the energy band from 0.3 keV to 10 keV with a field of view of 1.0 degree. The camera development is done at the Max-Planck-Institute for Extraterrestrial Physics and in particular the key component, the PNCCD sensor, has been designed and fabricated at the semiconductor laboratory of the Max-Planck Society. All produced devices have been tested and the best selected for the eROSITA project. Based on calculations, simulations, and experimental testing of prototype systems, the flight cameras have been configured. We describe the detector and its performance, the camera design and electronics, the thermal system, and report on the latest estimates of the expected radiation damage taking into account the generation of secondary neutrons. The most recent test results will be presented as well as the status of the instrument development.

Distributed Bragg reflectors with high reflectivity bands centered at wavelengths from 530 to 690 nm (green to red) based on AlP/GaP quarter-wave stacks are prepared on (001)GaP using gas-source molecular-beam epitaxy. Additionally, the complex refractive index of AlP is measured using spectroscopic ellipsometry within the range of 330–850 nm in order to facilitate an accurate reflector design. Structures consisting of 15 quarter-wave stacks reach a peak reflectance between 95% and 98%, depending on the spectral position of the maximum.