Gamma-ray lens development status for a European gamma-ray imager

Abstract

A breakthrough in the sensitivity level of the hard X-/gamma-ray telescopes, which today are based on detectors that view the sky through (or not) coded masks, is expected when focusing optics will be available also in this energy range. Focusing techniques are now in an advanced stage of development. To date the most efficient technique to focus hard X-rays with energies above 100 keV appears to be the Bragg diffraction from crystals in transmission configuration (Laue lenses). Crystals with mosaic structure appear to be the most suitable to build a Laue lens with a broad passband, even though other alternative structures are being investigated. The goal of our project is the development of a broad band focusing telescope based on gamma-ray lenses for the study of the continuum emission of celestial sources from 60 keV up to >600 keV. We will report details of our project, its development status and results of our assessment study of a lens configuration for the European Gamma Ray Imager (GRI) mission now under study for the ESA plan Cosmic Vision 2015-2025.

GRI: focusing on the evolving violent universe

“…Laboratory work and balloon campaigns have provided the proof-of-principle for using Laue lenses as focusing devices in gamma-ray telescopes [1,[7][8][9], and concept studies by CNES and ESA have demonstrated that such an instrument is technically feasible and affordable [3,6]. Complemented by a hard X-ray telescope based on a single-reflection multilayer coated concentrator, a broad-band energy coverage can be achieved that allows detailed studies of astrophysical sources at unprecedented sensitivity and angular resolution, from ∼10 keV up to at least 1 MeV.…”

Laue Gamma-Ray Lenses for Space Astrophysics: Status and Prospects

“…It can be seen [11,[29][30][31] that, even if a higher mosaicity gives a larger lens effective area (see Figure 9), a higher spread also produces a larger defocusing of the reflected photons in the focal plane and thus a lower lens sensitivity.…”

“…The optical properties of a lens, for both on-axis and off-axis incident photons, have been investigated by means of Monte Carlo (MC) simulations [11,31]. For flat crystal tiles, the Point Spread Function (PSF) depends on the crystal size, on their mosaicity and on the accuracy of their positioning in the lens.…”

“…A thorough discussion of the science case has been carried out in the context of the mission proposal Gamma Ray Imager (GRI), submitted to ESA in response to the first AO of the 'Cosmic Vision 2015-2025 plan [9] (but see also [10][11][12]). We summarize here some of these issues.…”

Self-standing bent silicon crystals for very high efficiency Laue lens

“…However, to take full advantage of this potential, the next generation of instruments working in this energy domain will have to achieve an improvement in sensitivity by at least an order of magnitude with respect to existing telescopes [1]. Bragg diffraction in Laue geometry [2] is being proposed to efficiently concentrate photons at these energies [3,4].…”