Optimization of grazing incidence mirrors and its application to surveying X-ray telescopes

Osservatorio Astronomico di Brera, Via Bianchi 46, 23807 Merate (Lc), Italy

Corresponding author: S. Campana, campana@merate.mi.astro.it

Received: 15 November 2000
Accepted: 30 March 2001

Abstract

Grazing incidence mirrors for X-ray astronomy are usually designed in the parabola-hyperbola (Wolter I) configuration. This design allows for optimal images on-axis, which however degrade rapidly with the off-axis angle. Mirror surfaces described by polynomia (with terms higher than order two), have been put forward to improve the performances over the field of view. Here we present a refined procedure aimed at optimizing wide-field grazing incidence telescopes for X-ray astronomy. We improve the angular resolution over existing (wide-field) designs by ~20% . We further consider the corrections for the different plate scale and focal plane curvature of the mirror shells, which sharpen by another ~20% the image quality. This results in a factor of ~2 reduction in the observing time needed to achieve the same sensitivity over existing wide-field designs and of ~5 over Wolter I telescopes. We demonstrate that such wide-field X-ray telescopes are highly advantageous for deep surveys of the X-ray sky.