![]() Schematic layout of the RGS (from Brinkman et al. With the criterion above, this fraction is given approximately by sin(alpha)/sin(beta blaze) = 0.53 (ignoring obstruction by structural elements). This implies that only a fraction of the light exiting the telescope is intercepted by the Reflection Grating Array. The separation between the gratings was chosen to be as close as possible without vignetting the blaze wavelength. Because the outgoing rays reflect at larger angles than the incoming rays, neighbouring gratings within the array vignet part of the diffracted light. The diffraction efficiency is maximized when the incident and exit angles on the facets are equal. With this orientation, the light is primarily diffracted into the "inside" spectral orders, where "m" "alpha". The gratings are fabricated to have "blazed" groove profiles, where the facets are all tilted with respect to the grating plane. ), d is the groove spacing, "beta" is the angle between the outgoing ray and the grating plane, and "alpha" is the angle between the incoming ray and the grating plane referred to above. The dispersion equation for the spectrometer is given by: The gratings are located in a toroidal surface, formed by rotating the Rowland circle about an axis passing through the telescope focus and the first order blaze focus. The grating stack consists of 182 identical gratings, mounted at grazing incidence to the beam in the classical configuration. The relevant interconnecting harness between the different units.įirst order blaze wavelength (lambda blaze).Four Digital Electronic units ( RDE), two for each chain.Two Analogue Electronic units ( RAE), containing prime and redundant functions.Two Focal Plane Camera units ( RFC), each including a stand-off structure, a radiator and the detector itself with its front-end electronics.Two Reflection grating Arrays units ( RGA), directly attached to the corresponding mirror assemblies.The instrument consists of two identical chains with the following units: For each photon, the position and the energy is measured: the position to determine the high resolution X-ray spectrum as diffracted by the grating module, and the energy and position to separate the contributions from the various overlapping grating orders (and from the in-flight calibration source) and to reduce the background. Nine large format back-illuminated CCDs are operated in single photon counting and frame transfer mode at a temperature of -80 C. The undeflected light passes through and is intercepted by EPIC-MOS in the telescope focal plane. The grating stack intercepts roughly half of the X-ray light and deflects it to a strip of CCD detectors offset from the telescope focal plane. ![]() The RGS design incorporates an array of reflection gratings placed in the converging beam at the exit from the X-ray telescope. The effective area peaks around 15 Å (first order) at about 150 cm 2 for the two spectrometers. The RGS instruments achieve high resolving power (150 to 800) over a range from 5 to 35 Å (in the first spectral order). Each RGS consists of an array of reflection gratings which diffracts the X-rays to an array of dedicated charge coupled devices (CCD) detectors. Behind two of the three telescopes, about half of the X-ray light is utilized by the Reflection Grating Spectrometers (RGS). Imaging CCD detectors are placed in the focus of each telescope. The payload comprises three co-aligned high throughput telescopes with a FOV of 30 arcmin and spatial resolution of about 6 arcsec (FWHM). The X-ray Multi Mirror (XMM-Newton) mission is the second of the four cornerstone projects of the ESA long-term programme for space, Horizon 2000. 2001, A&A 365, L7įurther information can be obtained from the XMM-Newton Users' Handbook Introduction 1998, in "Proceedings of the First XMM Workshop: Science with XMM", ESTEC, Noordwijk, The Netherlands, ed. This description is mostly based on the information contained in the papersīrinkman, A. ![]() The Reflection Grating Spectrometer (RGS) onboard XMM-Newton
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