<title>Medium-sized grazing incidence high-energy x-ray telescopes employing continuously graded multilayers</title>

Abstract

We present a concept of continuously graded multilayer structures for medium-sized x-ray telescopes which is based on several material combinations. We show that the theoretical reflectivity characteristics of these structures make them very advantageous when applied to high energy x-ray grazing incidence telescopes. We consider the performance of continuously graded Ni/C multilayers in a multi-focus, Kirkpatrick-Baez geometry and show a significant improvement when compared to standard coatings of gold. For a total length of 3.3 m, a total aperture of 48 cm by 48 cm, and 64 foci, we obtain an effective area of 250 cm<SUP>2</SUP> at 60 keV and a FWHM field of view of 6 feet. We also show that a modular array of conical telescopes (conical approximation to a Wolter-I geometry), with the same length and aperture provides similar effective areas. Energy-dispersive x-ray reflectivity data (15 - 70 keV) is presented for the first continuously graded multilayer of this kind.