eROSITA camera design and first performance measurements with CCDs

The German X-ray observatory eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the prime instrument of the new Spectrum-RG mission. Launch of the Russian satellite is planned for the year 2011. The scientific goal of eROSITA is primarily the detection and analysis of 100 thousand clusters of galaxies in order to study the large scale structures in the Universe and to test cosmological models. The therefore required large effective area is obtained by an array of seven identical and parallel aligned Wolter-I telescopes. In the focus of each mirror module, there is a large frame store pnCCD detector, providing a field of view of 1° in diameter. The same X-ray detector type will also be applied for ART-XC, another grazing-incidence telescope system aboard Spectrum-RG, which permits the detection of heavily obscured X-ray sources. These scientific instruments allow the exploration of the X-ray Universe in the energy band from 0.3 keV to 11 keV. During a mission time of at least five years, an all-sky survey, wide as well as deep surveys and pointed observations will be performed. Approval and funding for eROSITA were granted by the German space agency DLR in April 2007. The conceptual design of the X-ray focal plane cameras is presented here comprising electrical, thermal, and mechanical aspects. Key part of the camera is the pnCCD detector chip, which is developed and produced in our semiconductor laboratory, the MPI Halbleiterlabor. The CCD was designed according to the specifications given by the scientific goals of eROSITA. The eROSITA CCD differs apparently from all previously produced frame store pnCCDs by its larger size and format. The CCD image area of the seven eROSITA cameras is in total 58 cm 2 large and their number of pixels is about seven times higher than that of the XMM-Newton pnCCD camera. First pnCCD devices were recently produced and tested. Their performance measurements and results are of most importance for eROSITA because the tested CCDs are the control sample of the flight detector production.