Grazing incidence at work: an outreach project to demonstrate the X-ray optics behaviour using the nested mirrors developed for the BeppoSAX X-ray satellite

Abstract

BeppoSAX was an Italian-Dutch satellite designed for X-ray observations, launched in 1996 and deactivated in 2002. It was the first satellite to precisely localize the Gamma Ray Bursts and to detect the X-ray emission due to the afterglow, a breakthrough discovery for high energy astrophysics that eventually placed such events at extra-galactic distances after many debates in the previous years. On board of the satellite there were four identical X-ray imaging telescopes based on grazing incidence mirrors, ranging between 1-10 keV in energy and with a spatial resolution <1 arcmin HEW. In order to limit the costs of the telescopes, the optics were assembled using nickel nested mirrors replicated via electroforming using masters. During the development of the instruments of BeppoSAX, two qualification models of the grazing mirrors were assembled and used for tests at various X-ray facilities; they are now in storage in Milano (Italy) at the INAF-IASF Institute and Brera Observatory. In this paper, we describe the setup we have built in order to use these models for an outreach program. The aim of this effort is to illustrate to students and teachers of secondary schools how a grazing mirror for X-ray astronomy works. A first, basic experiment shows the reflection of light at normal incidence: using two small face-to-face parabolic reflectors, a powerful lamp positioned in the focus of the first parabola can light a match fixed in the focus of the other reflector. A second experiment uses the nested mirror to show how to deflect photons using grazing incidence. In this case a plane wave, created with a light source and a Fresnel lens, enters in the front of the Beppo SAX optics made of several nested mirror shells and is focused exactly as for X-rays.