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Experimental verification of a micrometeoroid damage in the pn-CCD camera system aboard XMM-Newton

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The pn-CCD is the focal plane detector of one of the three X-ray telescopes aboard the XMM-Newton observatory. During revolution #156 more than 30 individual bright pixels lightened up out of approximately 150,000 pixels of the 6 cm × 6 cm large detector area. The amount of leakage current generated in the pixels cannot be explained by single heavy ions impact, however. We suggest that a micrometeoroid scattered off the mirror surface under grazing incidence reached the focal plane detector and produced the bright pixels. This proposal was studied by us experimentally at the Heidelberg dust accelerator. Micron-sized iron particles were accelerated to speeds of the order of 5 km/s impinging on the surface of an X-ray mirror under grazing incidence. Scatter products have been found with detectors placed behind the mirror. They have been analyzed by various methods to characterize their properties and the effects produced by them in the pn-CCD. Micrometeoroid damage to semiconductor detectors in the focus of grazing incidence optics might be of concern for future space projects with very large collecting area and are proposed to be studied in detail.

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