Francesco Mazzoleni

Characteristics of the flight model optics for the JET-X telescope onboard the Spectrum-X-Gamma satellite

The joint European x-ray telescope (JET-X) is one of the core scientific instruments of the RUssian SPECTRUM X-(gamma) astrophysics mission. JET-X is designed to study the emission from x-ray sources in the band of 0.3-10 keV; in particular to meet primary scientific goals in cosmology and extragalactic astronomy. JET-X consists of two identical, coaligned x-ray telescopes, each with a spatial resolution of better than 30 arcsec half energy width. Focal plane imaging is provided by cooled x-ray sensitive CCD detectors which combine high spatial resolution with good spectral resolution, including coverage of the iron line complex around 7 keV at a resolution of (Delta) E/E approximately 1.5 percent. Each telescope is composed of a nested array of 12 mirror shells with an aperture of 300 mm and focal length of 3500 mm; the total effective area is 330 cm2 at 1.5 keV and 145 cm2 at 8.1 keV. The mirror shells have a Wolter I geometry and are manufactured by an electroforming replica process. The paper presents the characteristic of the flight model x-ray optics.

Development of a Prototype Nickel Optic for the Constellation-X Hard-X-Ray Telescope

The Constellation-X mission planned for launch in 2015-2020 timeframe, will feature an array of Hard X-ray telescopes (HXT) with a total collecting area greater than 1500 cm at 40 keV. Two technologies are being investigated for the optics of these telescopes, one of which is multilayer-coated Electroformed-Nickel-Replicated (ENR) shells. The attraction of the ENR process is that the resulting full-shell optics are inherently stable and offer the prospect of better angular resolution which results in lower background and higher instrument sensitivity. We are building a prototype HXT mirror module using an ENR process to fabricate the individual shells.This prototype consists of 5 shells with diameters ranging from 15 cm to 28 cm with a length of 42.6 cm. The innermost of these will be coated with iridium, while the remainder will be coated with graded d-spaced W/Si multilayers. The assembly structure has been completed and last year we reported on full beam illumination results from the first test shell mounted in this structure. We have now fabricated and coated two (15 cm and 23 cm diameter) 100 micron thick shells which have been aligned and mounted. This paper presents the results of full beam illumination X-ray tests, taken at MPE-Panter. The HEW of the individual shells will be discussed, in addition to results from the full two shell optic test.

Manufacturing of Wolter-I mirror segments with slumped glass

In our ongoing studies of high precision glass slumping we have successfully formed the first Wolter-I X-ray mirror segments with parabola and hyperbola in one piece. It could be demonstrated that the excellent surface roughness of the 0.55 mm thick display glass chosen is conserved during the slumping process. The influence of several parameters of the process, such as maximum temperature, heating and cooling rates etc. have to be measured and controlled with adequate metrology. Currently, we are optimizing the process to reduce the figure errors down to 1 micrometer what will be the starting point for further, final figure error corrections. We point out that metrology plays an important role in achieving a high precision optics, i.e. an angular resolution of a few arcsec. In this paper we report on the results of our studies and discuss them in the context of the requirements for future X-ray telescopes with large apertures.

X-ray optics for the WFXT telescope

Wide field x-ray telescope (WFXT) is the core instrument of the Wide Angle X-ray Survey (WAXS) mission, which is aimed at conducting a high angular resolution, high sensitivity x- ray survey over a large solid angle of the sky. The project has been developed as a feasibility study in the frame of the Agenzia Spaziale Italiana (ASI) program for small-medium satellite mission. WFXT uses grazing incidence optics based on a new design where the Wolter I profile is substituted by a five term polynomial profile. The coefficients of the polynomium are optimized to obtain high spatial resolution over a field of view of about 1 degree. The WFXT optics consist of 25 nested shells. In order to have both a large effective area at low energies and a meaningful area at higher energies, a design consisting of 9 large mirror shells and 16 smaller shells, contributing mainly at higher energies, has been developed. The outermost and innermost mirror shells have a diameter of 600 and 226 mm, respectively. The total length of the mirror shells is 120 + 120 mm, while the focal length of the optical system is 3000 mm. For the WFXT optics, in addition to the well proved manufacturing process by nickel electroforming, we considered a novel replication technique for the manufacture of the mirrors which make use of ceramic material like Silicon Carbide in order to meet the stringent requirements of high spatial resolution and low weight. In this paper we give the details of the optical design and report the rest of the x-ray measurements of the prototypes of the outermost mirror shell manufactured with nickel and SiC.

Development of grazing-incidence multilayer mirrors by direct Ni electroforming replication: a status report

The Ni electroforming replication process has been used successfully by Beppo-SAX, JET-X/SWIFT, and XMM-Newton, to produce their gold-coated X-ray mirrors. The important feature of the technique is that, also with thin substrates, it is possible to achieve a good angular resolution, which is important for obtaining high signal-to-noise ratios in deep observations and imaging extended sources, while the assembly and integration of the monolithic shells is a relatively easy task. Two approaches can be used for the up grade of this technique also to the case of mirrors with multilayer coating, to be used in future hard X-ray missions: i) the direct replication of the mirror shell, after the deposition of the multilayer film on the master (mandrel) surface followed by the electroforming of the Ni walls, ii) the application of the multilayer film to the internal surface of Ni mirror shells, previously realized by replication. In this paper the last results achieved in Italy in the context of an activity aiming at the development of the former of the two methods will be presented and discussed.

Development of soft and hard x-ray optics for astronomy: progress report II and considerations on material properties for large-diameter segmented optics of future missions

In this paper we will review the activities devoted to the development of soft (0.1-10 keV) and hard (10-100 keV) X-ray optics for future astronomical missions that were carried out at the Brera Astronomical Observatory (OAB, Italy) during the last year. Concerning the soft X-ray optics, we are studying the approach based on the use of ceramic carriers for making monolithic Wolter I mirror shells of large diameter by epoxy replication. The ceramic materials investigated in our study are SiC and Alumina (Al2O3), respectively produced by Chemical Vapor Deposition and plasma spray. We fabricated a number of mirror shell prototypes (

Replication by Ni electroforming approach to produce the Con-X/HXT hard x-ray mirrors

PHI equals 60 cm) using carriers based on both materials. X-ray imaging tests performed at the PANTER X-ray facility (Germany) with a full illumination of the optics demonstrated that the mirror shells based on SiC show much better performances than in the case of Alumina. These results can be explained in terms of the thermal-mechanical parameters of the two materials, being in the case of SiC much more performing than for Alumina. Concerning the development of hard X-ray multilayer optics, we are exploring the approach based on Ni electroforming replication. In the last period of activity we in particular concentrated our work on the surface superpolishing methods for the mandrel to be used in the replication process, to be much improved with respect the case Au coated single layer mirrors for soft X-rays. Concerning the specific aspect of the mandrel superpolishing, the results that we obtained can be considered very good and it is possible to claim that we achieved the goal prefixed at the beginning of the development program. The last part of the paper is dedicated to theoretical considerations on large-size and low-weight optics based on segmented mirrors like e.g., those under study for the petals of the XEUS project. In particular, the expected imaging performances by segmented optics produced using different kinds of materials will be compared.

Calibration of hard x-ray (15 - 50 keV) optics at the MPE test facility PANTER

The NASAs Constellation X-Ray Mission consists of a Soft X-Ray Telescope (SXT) based on large collecting area optics plus a focusing Hard X-Ray Telescope (HXT) operating between 8 and 70 keV and possibly at even higher energy. The Con-X HXT will have a focal length of 10 m and graze angles are small (0.25 - 0.1 deg). The substrates will be coated with multilayers to enhance the reflectivity but single heavy element coatings are an alternative for the small diameter substrates of the set. Twelve copies of the HXT are distributed evenly among the four Con-X spacecrafts. With multiple telescopes it is appropriate to consider electroforming, the replication process used successfully by Beppo-SAX, JET-X/SWIFT, and XMM-Newton, to produce their substrates. The important feature of the technique is that for mirrors with aperture diameters less than 40 cm also with thin substrates it is possible to achieve good angular resolution, which is important for obtaining high signal-to-noise ratios in deep observations and imaging extended sources. We review the main results of our development study devoted to proving the feasibility of the process for the Con-X/HXT, with particular stress on demonstrating, not only by theoretical considerations but also presenting an important experimental proof, that we can satisfy the severe mass constraints of the mission still maintaining good imaging capabilities.

Development of soft and hard x-ray optics for astronomy

The Max-Planck-Institut fuer extraterrestrische Physik (MPE) in Garching, Germany, operates the large X-ray beam line facility PANTER for testing astronomical systems. At PANTER a number of telescopes like EXOSAT, ROSAT, SAX, JET-X, ABRIXAS, XMM and SWIFT operating in the soft energy range (0.02 - 15 keV) have been successfully calibrated. In the present paper we report on an important upgrade recently implemented that enables the calibration of hard X-ray optics (from 15 up to 50 keV). Currently hard X-ray optics based on single and multilayer coating are being developed for several future X-ray missions. The hard X-ray calibrations at PANTER are carried out by a high energy source based on an electron gun and several anodes, able to cover the energy range from 4.5 up to 50 keV. It provides fluxes up to 104 counts/sec/cm2 at the instrument chamber with a stability better than 1%. As detector a pn-CCD camera operating between 0.2 and 50 keV and a collecting area of 36 cm2 is used. Taking into account the high energy resolution of the CCD (145 eV at 6 keV), a very easy way to operate the facility in hard X-ray is in energy-dispersive mode (i.e. with a broad-band beam). A double crystal monochromator is also available providing energies up to 20 keV. In this paper we present the first results obtained by using PANTER for hard X-ray characterizations, performed on prototype multilayer optics developed by the Osservatorio Astronomico di Brera (OAB), Milano, Italy, and the Harvard-Smithsonian Center for Astrophysics (CfA), Cambridge, MA, USA.

X-ray optics for the JET-X experiment aboard the Spectrum X satellite

For the next generation X-ray astronomy missions two main technological goals have to be achieved: (1) the possibility of making soft X-ray (0.1 - 10 keV) optics with much larger effective areas compared to the missions Chandra and XMM- Newton but still maintaining good angular resolution (better than 15 arcsec); (2) the extension of the use of focusing optics to the hard X-ray energy band (E equals 10 - 100 keV) by means of multilayer coating optics. The Brera Astronomical Observatory (Italy) is currently involved in technological development activities for the achievement of both these objectives. Concerning the realization of large diameter soft X-ray optics with low weight and good imaging capabilities, our efforts are devoted to the development of carriers made of ceramic materials like SiC and Alumina (Al2O3). The low density and the good mechanical parameters of these materials are very promising for this purpose. The technology for manufacturing hard X-ray optics based on multilayer mirrors, will be instead directly derived, with opportune modifications, from the replication process based on Nickel electroforming. This approach was already successfully used for the fabrication of the soft X-ray optics with Au coating of the Beppo-SAX, JET-X, SWIFT and XMM-Newton space experiments. In this case the use of Nickel instead of ceramics for the realization of the mirror carriers remains appropriate, due to the fact that, also for long focal length, hard X-ray telescopes are characterized by small diameters. In this paper we will present the more recent progresses achieved in pursuing these studies.