PST measurements and wide angle straylight analyses of the XMM (X-Ray Multi Mirrror) telescopes

The high throughput X-ray spectroscopy mission XMM is the second "Cornerstone" project in the ESA long term Programme for Space Science. This observatory has at its heart three heavily nested Welter I grazing incidence X-ray telescope. The telescopes are equipped with non-dispersive spectroscopic imaging instruments (EPIC, European Photon Imaging Camera) and medium resolution dispersive spectroscopic instruments (RGS, Reflection Grating Spectrometer). Because of the sensitivity of the XMM instruments X-ray detectors in the visible wavelength range, a high suppression of the visible radiation emitted from out-of-field sources (earth, sun) must be ensured, The straylight reduction capability is quantified by the PST (Point Source Transmittance). The experimental verification of the PST on the XMM flight model mirror modules for off-axis angles between 1 degrees and 85 degrees is presented in this paper. For the first time a straylight test of a complete telescope was performed in air measuring the telescope PST over a range of 9 orders of magnitude (10(-2) to 10(-11)).