A wide field X-ray telescope for astronomical survey purposes: from theory to practice

Conconi, P.; Campana, S.; Tagliaferri, G.; Pareschi, G.; Citterio, O.; Cotroneo, Vincenzo; Proserpio, L.; Civitani, M.

doi:10.1111/j.1365-2966.2010.16513.x

Cited by 22 publications

(26 citation statements)

References 29 publications

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“…This approach was previously adopted to optimize the PSF across the FoV of X-ray grazing incidence telescopes by Conconi et al (2010). It follows a method that is similar to the Ritchey-Chretien design since on-axis aberrations are admitted in order to cancel off-axis aberrations and obtaining in that way a PSF response flat across the entire FoV.…”

Section: Astri Sst-2m Optical Designmentioning

confidence: 99%

“…Wolter's approach was later adopted for the design of X-ray astronomical telescopes based on grazing incidence optics, and a number of X-ray telescopes were realized (Aschenbach 1985(Aschenbach , 2009. Following the approach initially suggested by Burrows et al (1992), Conconi et al (2010) showed that different Wolter-like designs could be obtained by expanding as a power series the primary and secondary mirrors' profiles in order to increase the angular resolution at large offaxis positions, at the expense of the on-axis performances. Also, the curvature of the focal plane could be optimized, similarly to Couder's solution for normal incidence mirrors.…”

Section: Introductionmentioning

confidence: 99%

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First optical validation of a Schwarzschild Couder telescope: the ASTRI SST-2M Cherenkov telescope

Giro

Canestrari

Sironi

et al. 2017

A&A

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Context. The Cherenkov Telescope Array (CTA) represents the most advanced facility designed for Cherenkov Astronomy. ASTRI SST-2M has been developed as a demonstrator for the Small Size Telescope in the context of the upcoming CTA. Its main innovation consists in the optical layout which implements the Schwarzschild-Couder configuration and is fully validated for the first time. The ASTRI SST-2M optical system represents the first qualified example of a two-mirror telescope for Cherenkov Astronomy. This configuration permits us to (i) maintain high optical quality across a large field of view; (ii) demagnify the plate scale; and (iii) exploit new technological solutions for focal plane sensors. Aims. The goal of the paper is to present the optical qualification of the ASTRI SST-2M telescope. The qualification has been obtained measuring the point spread function (PSF) sizes generated in the focal plane at various distances from the optical axis. These values have been compared with the performances expected by design. Methods. After an introduction on Gamma-ray Astronomy from the ground, the optical design of ASTRI SST-2M and how it has been implemented is discussed. Moreover, the description of the set-up used to qualify the telescope over the full field of view is shown. Results. We report the results of the first-light optical qualification. The required specification of a flat PSF of ∼10 arcmin in a large field of view (∼10 • ) has been demonstrated. These results validate the design specifications, opening a new scenario for Cherenkov Gamma-ray Astronomy and, in particular, for the detection of high-energy (5-300 TeV) gamma rays and wide-field observations with CTA.

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Section: Astri Sst-2m Optical Designmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

First optical validation of a Schwarzschild Couder telescope: the ASTRI SST-2M Cherenkov telescope

Giro

Canestrari

Sironi

et al. 2017

A&A

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“…A module design with mirror lengths scaled to the diameter has already been studied by Conconi et al (2010) to minimize the defocusing due to the field curvature in the WFXT telescope. Therefore, after choosing a sequence of mirror lengths according Eq.…”

Section: Design Of the Mirror Modulementioning

confidence: 99%

Optics for X-ray telescopes: analytical treatment of the off-axis effective area of mirrors in optical modules

Spiga

2011

A&A

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Context. Optical modules for X-ray telescopes comprise several double-reflection mirrors operating in grazing incidence. The concentration power of an optical module, which determines primarily the telescope's sensitivity, is in general expressed by its on-axis effective area as a function of the X-ray energy. Nevertheless, the effective area of X-ray mirrors in general decreases as the source moves off-axis, with a consequent loss of sensitivity. To make matters worse, the dense nesting of mirror shells in an optical module results in a mutual obstruction of their aperture when an astronomical source is off-axis, with a further effective area reduction. Aims. To ensure the performance of X-ray optics for new X-ray telescopes (like NuSTAR, NHXM, ASTRO-H, IXO), their design entails a detailed computation of the effective area over all the telescope's field of view. While the effective area of an X-ray mirror is easy to predict on-axis, the same task becomes more difficult for a source off-axis. It is therefore important to develop an appropriate formalism to reliably compute the off-axis effective area of a Wolter-I mirror, including the effect of obstructions. Methods. Most of collecting area simulation for X-ray optical modules has been so far performed along with numerical codes, involving ray-tracing routines, very effective but in general complex, difficult to handle, time consuming and affected by statistical errors. In contrast, in a previous paper we approached this problem from an analytical viewpoint, to the end of simplifying and speeding up the prediction of the off-axis effective area of unobstructed X-ray mirrors with any reflective coating, including multilayers. Results. In this work we extend the analytical results obtained: we show that the analytical formula for the off-axis effective area can be inverted, and we expose in detail a novel analytical treatment of mutual shell obstruction in densely nested mirror assemblies, which reduces the off-axis effective area computation to a simple integration. The results are in excellent agreement with the findings of a detailed ray-tracing routine.

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“…The current WFXT design is based on thin nested shells with polynomial profiles [3], radius-dependent length, and with the intersection planes between the two pseudo-cylindrical reflecting surfaces shifted one with respect to the other for each mirror shell. The result of the entire set of assembled shells assumes a sort of "butterfly-like" configuration [4]. The WFXT optical assembly will be composed by three identical modules, whose characteristics are reported in Table 1.…”

Section: Introductionmentioning

confidence: 99%

Design and development by direct polishing of the WFXT thin polynomial mirror shells

Proserpio

Campana

Citterio

et al. 2017

International Conference on Space Optics — ICSO 2010

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The Wide Field X-ray Telescope (WFXT) is a medium class mission proposed to address key questions about cosmic origins and physics of the cosmos through an unprecedented survey of the sky in the soft X-ray band (0.2-6 keV) [1], [2]. In order to get the desired angular resolution of 10 arcsec (5 arcsec goal) on the entire 1 degrees Field Of View (FOV), the design of the optical system is based on nested grazing-incidence polynomial profiles mirrors, and assumes a focal plane curvature and plate scale corrections among the shells. This design guarantees an increased angular resolution also at large off-axis positions with respect to the usually adopted Wolter I configuration. In order to meet the requirements in terms of mass and effective area (less than 1200 kg, 6000 cm 2 @ 1 keV), the nested shells are thin and made of quartz glass. The telescope assembly is composed by three identical modules of 78 nested shells each, with diameter up to 1.1 m, length in the range of 200-440 mm and thickness of less than 2.2 mm. At this regard, a deterministic direct polishing method is under investigation to manufacture the WFXT thin grazing-incidence mirrors made of quartz. The direct polishing method has already been used for past missions (as Einstein, Rosat, Chandra) but based on much thicker shells (10 mm ore more). The technological challenge for WFXT is to apply the same approach but for 510 times thinner shells. The proposed approach is based on two main steps: first, quartz glass tubes available on the market are ground to conical profiles; second the pre-shaped shells are polished to the required polynomial profiles using a CNC polishing machine. In this paper, preliminary results on the direct grinding and polishing of prototypes shells made by quartz glass with low thickness, representative of the WFXT optical design, are presented.

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A wide field X-ray telescope for astronomical survey purposes: from theory to practice

Cited by 22 publications

References 29 publications

First optical validation of a Schwarzschild Couder telescope: the ASTRI SST-2M Cherenkov telescope

First optical validation of a Schwarzschild Couder telescope: the ASTRI SST-2M Cherenkov telescope

Optics for X-ray telescopes: analytical treatment of the off-axis effective area of mirrors in optical modules

Design and development by direct polishing of the WFXT thin polynomial mirror shells

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