Marco W. Beijersbergen

Calibration of the first XMM flight mirror module: I. Image quality

The high throughput x-ray spectroscopy mission (XMM) is a Cornerstone Project in the ESA long-term Program for Space Science. The satellite observatory uses three grazing incidence mirror modules coupled to reflection grating spectrometers and x-ray CCD cameras. Each XMM mirror module consists of 58 Wolter I mirrors which are nested in a coaxial and confocal configuration. The calibration of the mirror system includes the development of a representative numerical model and its validation against extensive calibration test performed on ground at the CSL and PANTER test facilities. The present paper describes the calibration of the x-ray image quality of the first XMM flight mirror module.

Microchannel-plate-based x-ray optics

X-ray optics based on micro-channel plates (MCPs) offer some distinctive advantages over conventional technologies used to produce imagin optics for astrophysics applications. Such micro-pore optics (MPOs) are far lighter and allow a larger stacking density than optics based on metallic foils or plates. Until recent, x-ray optics based on MCPs were not feasible or useful because of the limited quality of the MCPs. We have produced thick square pore MPOs of improved quality and have developed methods to stack the channels in a radial pattern, as required for imagin optics based on Wolter type I or II designs. The individual plates were tested in synchrotron radiation facilities and conventional beam lines to determine their geometric and surface scattering properties.

Performance characterization of silicon pore optics

The characteristics of the latest generation of assembled silicon pore X-ray optics are discussed in this paper. These very light, stiff and modular high performance pore optics (HPO) have been developed [1] for the next generation of astronomical X-ray telescopes, which require large collecting areas whilst achieving angular resolutions better than 5 arcseconds. The suitability of 12 inch silicon wafers as high quality optical mirrors and the automated assembly process are discussed elsewhere in this conference. HPOs with several tens of ribbed silicon plates are assembled by bending the plates into an accurate cylindrical shape and directly bonding them on top of each other. The achievable figure accuracy is measured during assembly and in test campaigns at X-ray testing facilities like BESSY-II and PANTER. Pencil beam measurements allow gaining information on the quality achieved by the production process with high spatial resolution. In combination with full beam illumination a complete picture of the excellent performance of these optics can be derived. Experimental results are presented and discussed in detail. The results of such campaigns are used to further improve the production process in order to match the challenging XEUS requirements [2] for imaging resolution and mass.

Novel micropore x-ray optics produced with microchannel plate technology

A novel type of micro-pore optics for the X-ray regime has been developed. These optics have a radial design instead of the square packing in the more traditional Lobster-eye optics. With such a design true imaging, without a crucifix in the focus, can be achieved. We demonstrate that the walls inside the square pores are good enough to produce sub- arcminute focussing up to photon energies above 10 keV. The current performance of the optics is limited by large-scale distortions of the plates, probably caused by the method to fuse the fibers together.

Micropore x-ray optics developments and application to an x-ray timing mission

Very lightweight X-ray optics are being developed by ESA and its industrial partners, for a number of X-ray astronomy and planetary missions. These developments could significantly improve the performance of future X-ray timing instrumentation. Based on Micro-Channel Plate (MCP) technology, the novel optics effectively reduce the mirror thickness by almost two orders of magnitude, and therefore also the mass of the telescope optics. Very large collecting areas become feasible for space implementation, especially as required for X-ray timing observations. Furthermore this technology leads to much reduced detector sizes due to the use of imaging X-ray optics. This dramatically improves the detected signal-to-noise ratios, as well as introducing photon collection areas sufficiently large as to study temporal phenomena on the millisecond time scale. This is particularly important to improve the studies of compact X-ray sources, both for improving the signal to noise ratios in temporal bins so that spectral or fluctuation analyses are improved, and for extending the range of measurements to fainter classes of objects. We present a brief overview of the MCP micro-pore optics technology and a possible design for an X-ray timing mission based on this technology and we analyze the performance of such mission.

HERMES: an imaging x-ray fluorescence spectrometer for the BepiColombo mission to Mercury

We describe HERMES (High Energy Remote-Sensing of Mercurys Surface), a novel X-ray imaging spectrometer for potential accommodation in the Mercury Planetary Orbiter (MPO) component of ESAs BepiColombo mission to Mercury. The instrument combines recently developed micro channel plate optics with large-format compound semiconductor imaging arrays. MCP optics offer the distinct advantage of a large collecting area coupled to arcminute angular resolution in a light-weight package and short focal length. Measurements on a prototype optic indicate it should be possible to achieve an angular resolution below 1 arcmin over a fov of 1 degree(s). Energy resolution of 270 eV FWHM at 5.9 keV has been achieved at room temperature for a prototype GaAs array. We estimate that HERMES will detect ~2000 x-ray fluorescent photons s-1 from the surface of Mercury during solar quiet conditions at the pericenter of the orbit. The maximum expected surface spatial resolution from this altitude is ~200m and the fov 40 km2. Over the orbiters 2 year mission life, HERMES will provide the first very high resolution compositional maps of any planetary surface.

Calibration of the first XXM flight mirror module: II. Effective area

The High Throughput X-ray Spectroscopy Mission (XMM) is a Cornerstone Project in the ESA long-term Programme for Space Science. The satellite observatory uses three grazing incidence mirror modules coupled to reflection grating spectrometers and X-ray CCD cameras. Each XMM mirror module consists of 58 Wolter I mirrors which are nested in a coaxial and cofocal configuration. The calibration of the mirror system includes the development of a representative numerical model and its validation against extensive calibration tests performed on ground at the CSL and PANTER test facilities. The present paper describes the calibration of the x-ray effective area of the first XMM flight mirror module.n nKeywords: XMM, X-ray astronomy, Wolter I telescope, grazing incidence optics

Development of x-ray optics at ESA

At the European Space Agency (ESA) X-ray optics are being developed for future astrophysics and planetary missions. The cosmology mission XEUS requires very large effective area X-ray optics which high angular resolution. This implies a large aperture for a single telescope system, which will necessarily require assembly in space from basic mirror modules known as petals. The technology for the implementation of the Wolter-I design is based on the heritage of the XMM-Newton optics, but requires substantial further research and development. With 6 m2 effective area at 1 keV the XEUS optics is initially composed of 32 petals arranged in a circular aperture of 4.5m diameter, compatible with single Arian 5 launch into the XEUS orbit. Utilising the available infrastructure at the International Space Station (ISS) 96 additional petals, organised into 8 segments, are added to XEUS, increasing the effective area to 30 m2. Key aspects of the XEUS optics are therefore low-mass design, industrialisation of the production and ISS compatibility. As a potential optics for a remote sensing X-ray fluorescence spectrometer, extremely low mass Wolter-I optics are being developed. Based on Micro-Channel Plates (MCP), the mirror thickness can be dramatically reduced, making an accommodation on such missions as the Mercury orbiter of BeppiColombo possible. With a resolution of about 1 arcminute and compact construction, such imaging X-ray optics are well matched to modern Si or GaAs based detector arrays and will allow the mapping of the planetary surface in fluorescent X-ray light with unprecedented sensitivity.

X-ray evolving universe spectroscopy mission (XEUS): x-ray mirror design and technology

To achieve the demanding aims of XEUS, which involve the detection of sources as faint as 10-18 ergs cm-2s-1 a large x-ray mirror will need to be developed. This core scientific aim implies that the XEUS mirror needs to have an effective collection area at 1 keV of 30 m2 coupled to a spatial resolution on-axis of between 2 and 5 arcsec, so as to avoid source confusion at these very faint flux levels. Finally a field of view of at least 5 arcmin must be covered so as to ensure that a significantly large population of high redshift x-ray sources can be observed in a single pointing over the energy band from 0.05-30 keV. Clearly the key characteristics of XEUS is the large x-ray mirror aperture coupled to the high spatial resolution. The XEUS mirror aperture of 10 m diameter is divided into annuli with each annulus subdivided into sectors. The basic mirror unit therefore consist of a set of heavily stacked thin mirror plates each retaining the correct geometry. This unit is known as a mirror petal and constitutes a complete free-standing calibrated part of the overall XEUS mirror.

High-resolution micropore x-ray optics produced with microchannel plate technology

Using the technology that has been developed over many years for the fabrication of glass micro-channel plates, a prototype micro-pore optic has been produced that is a very light and compact implementation of a Wolter-I optic for X-ray imaging. With this prototype true Wolter-I imaging has been observed for the first time in a micro-pore optic. Individual fibers in the plates are found to be quite good, with a surface roughness permitting application at medium X-ray energies. The image quality and effective area is however seriously reduced by random tilt errors of multifibers in the plates. If this limitation can be overcome, this technology would allow very light and compact X-ray telescopes to be built. A design is presented that already provides a considerable effective area for soft X-rays using the properties of the surfaces obtained in this program.