Benedikt Menz

In focus measurements of IXO type optics using the new PANTER X-ray test facility extension

Future large X-ray observatories in space will require mirrors with large effective areas and long focal lengths to accomplish the proposed science. ESA programs for developing lightweight optics based on modules of silicon pore optics (SPO) and slumped glass optics (SGO) were put in place for the IXO mission (f=20m, r≈1m). To test such optics the MPE PANTER X-ray test facility has been upgraded / extended with support from ESA to accommodate in-focus measurements of such optics modules. We describe the extension to PANTER and the first results obtained from measuring such SPO and SGO modules during commissioning.

THE IMAGING PROPERTIES OF THE GAS PIXEL DETECTOR AS A FOCAL PLANE POLARIMETER

ABSTRACTX-rays are particularly suited to probe the physics of extreme objects. However, despite the enormousimprovements of X-ray Astronomy in imaging, spectroscopy and timing, polarimetry remains largelyunexplored. We propose the photoelectric polarimeter Gas Pixel Detector (GPD) as an instrumentcandidate to fill the gap of more than thirty years of lack of measurements. The GPD, in the focusof a telescope, will increase the sensitivity of orders of magnitude. Moreover, since it can measurethe energy, the position, the arrival time and the polarization angle of every single photon, allows toperform polarimetry of subsets of data singled out from the spectrum, the light curve or the imageof source. The GPD has an intrinsic very fine imaging capability and in this work we report on thecalibrationcampaign carriedout in 2012at the PANTER X-raytest facility of the Max-Planck-Institutfu¨r extraterrestrische Physik of Garching (Germany) in which, for the first time, we coupled it to aJET-X optics module with a focal length of 3.5 m and an angular resolution of 18 arcsec at 4.5 keV.This configuration was proposed in 2012 aboard the X-ray Imaging Polarimetry Explorer (XIPE) inresponse to the ESA call for a small mission. We derived the imaging and polarimetric performancefor extended sources like Pulsar Wind Nebulae and Supernova Remnants as case studies for the XIPEconfiguration, discussing also possible improvements by coupling the detector with advanced optics,having finer angular resolution and larger effective area, to study with more details extended objects.Keywords: X-ray polarimetry, X-ray telescope, angular resolution

X-ray optical units made of glass: achievements and perspectives

Future X-ray telescopes with very large collecting area, like the proposed Athena with more than 2 m2 effective area at 1 keV, need to be realized as assemblies of a large number of X-ray optical units, named X-ray Optical Units (XOUs). The Brera Astronomical Observatory (INAF-OAB) is developing a new technology to manufacture these modular elements, compatible with an angular resolution of 5 arcsec HEW (Half-Energy-Width). This technique consists in stacking in a Wolter-I configuration several layers of thin foils of glass, previously formed by direct hot slumping. The achievable global angular resolution of the optics relies on the required surface shape accuracy of slumped foils, on the smoothness of the mirror surfaces and on the correct integration and co-alignment of the mirror segments operated trough a dedicated Integration Machine (IMA). In this paper we provide an overview of the project development, reporting on the very promising results achieved so far, including in-focus full illumination X-ray tests of the prototype (Proof of Concept, POC#2, integrated at the beginning of 2013) for which an HEW of 22.1’’ has been measured at Panter/MPE. Moreover we report on the on-going activities, with a new integrated prototype (PoC#3). X-ray test in pencil beam revealed that at least a segment between two external ribs is characterized by an HEW well below 10’’. Lastly, the overall process up-grade to go from 20 m to 12m focal length (to be compatible with Athena+ configuration) is presented.

Direct hot slumping and accurate integration process to manufacture prototypal X-ray optical units made of glass

X-ray telescopes with very large collecting area, like the proposed International X-ray Observatory (IXO, with around 3 m2 at 1 keV), need to be composed of a large number high quality mirror segments, aiming at achieving an angular resolution better than 5 arcsec HEW (Half-Energy-Width). A possible technology to manufacture the modular elements that will compose the entire optical module, named X-ray Optical Units (XOUs), consists of stacking in Wolter-I configuration several layers of thin foils of borosilicate glass, previously formed by hot slumping. The XOUs are subsequently assembled to form complete multi-shell optics with Wolter-I geometry. The achievable global angular resolution of the optic relies on the required surface shape accuracy of slumped foils, on the smoothness of the mirror surfaces and on the correct integration and co-alignment of the mirror segments. The Brera Astronomical Observatory (INAF-OAB) is leading a study, supported by ESA, concerning the implementation of the IXO telescopes based on thin slumped glass foils. In addition to the opto-mechanical design, the study foresees the development of a direct hot slumping thin glass foils production technology. Moreover, an innovative assembly concept making use of Wolter-I counter-form moulds and glass reinforcing ribs is under development. The ribs connect pairs of consecutive foils in an XOU stack, playing a structural and a functional role. In fact, as the ribs constrain the foil profile to the correct shape during the bonding, they damp the low-frequency profile errors still present on the foil after slumping. A dedicated semirobotic Integration MAchine (IMA) has been realized to this scope and used to build a few integrated prototypes made of several layers of slumped plates. In this paper we provide an overview of the project, we report the results achieved so far, including full illumination intra-focus X-ray tests of the last integrated prototype that are compliant with a HEW of around 17’’.

Development and testing of the eROSITA mirror modules

MPE will provide the X-ray Survey Telescope eROSITA for the Russian Spektrum-Roentgen-Gamma Mission. The mirror system consists of a compact bundle of seven co-aligned mirror modules with a focal length of 1600 mm and 54 nested mirror shells each. The 61 arcmin field-of-view (FoV) will yield a high grasp of about 1000 cm2deg2 around 1 keV. An angular resolution of 15 arcsec HEW on-axis (resulting in an average angular resolution of ~26 arcsec HEW over the field-of-view and ~30 arcsec including all optical and spacecraft error contributions) will help distinguish point sources from extended emission of galaxy clusters which are relevant for cosmological studies. During a four year allsky survey eROSITA will generate a new rich database of X-ray sources. In a second phase of the mission eROSITA will also perform pointed observations. After a mirror development program the integration of flight mirror modules started in early 2011. Currently, the manufacturing of flight modules is ongoing and some of the partially integrated ones have already been X-ray tested. Calibration of completed mirror modules will start end of 2012. Parallel to the X-ray mirrors we have developed an X-ray baffle to suppress stray light from single reflections. It consists of precisely shaped and welded concentric Invar foils which will be mounted on top of each mirror module and aligned by optical means. We report on the design and the mirror development program including the X-ray baffle and present the latest results from X-ray measurements.

Line spread functions of blazed off-plane gratings operated in the Littrow mounting

Abstract. Future soft x-ray (10 to 50 Å) spectroscopy missions require higher effective areas and resolutions to perform critical science that cannot be done by instruments on current missions. An x-ray grating spectrometer employing off-plane reflection gratings would be capable of meeting these performance criteria. Off-plane gratings with blazed groove facets operating in the Littrow mounting can be used to achieve excellent throughput into orders achieving high resolutions. We have fabricated two off-plane gratings with blazed groove profiles via a technique that uses commonly available microfabrication processes, is easily scaled for mass production, and yields gratings customized for a given mission architecture. Both fabricated gratings were tested in the Littrow mounting at the Max Planck Institute for Extraterrestrial Physics (MPE) PANTER x-ray test facility to assess their performance. The line spread functions of diffracted orders were measured, and a maximum resolution of 800±20 is reported. In addition, we also observe evidence of a blaze effect from measurements of relative efficiencies of the diffracted orders.

Performance testing of an off-plane reflection grating and silicon pore optic spectrograph at PANTER

Abstract. An x-ray spectrograph consisting of aligned, radially ruled off-plane reflection gratings and silicon pore optics (SPO) was tested at the Max Planck Institute for Extraterrestrial Physics PANTER x-ray test facility. SPO is a test module for the proposed Arcus mission, which will also feature aligned off-plane reflection gratings. This test is the first time two off-plane gratings were actively aligned to each other and with an SPO to produce an overlapped spectrum. We report the performance of the complete spectrograph utilizing the aligned gratings module and plans for future development.

Studying ATHENA optics with divergent and collimated x-ray beams

An open question in the measurement of X-ray optics for satellite experiments is what the PSF (point spread function) looks like in orbit and what the focal length for a source at infinite distance is. In order to measure segmented optics as proposed for ATHENA a collimated X-ray beam with a size of several square centimeters is necessary. We showed that by using a zone plate such a collimated beam can be achieved. We discuss here the requirements such a zone plate collimator has to comply in order to characterize with this collimator an ATHENA type optic. Additional we can present results obtained with a first version of such a collimator and can show so the proof of principle.

Re-testing the JET-X Flight Module No. 2 at the PANTER facility

The Joint European X-ray Telescope (JET-X) was the core instrument of the Russian Spectrum-X- γ space observatory. It consisted of two identical soft X-ray (0.3–10 keV) telescopes with focusing optical modules having a measured angular resolution of nearly 15 arcsec. Soon after the payload completion, the mission was cancelled and the two optical flight modules (FM) were brought to the Brera Astronomical Observatory where they had been manufactured. After 16 years of storage, we have utilized the JET-X FM2 to test at the PANTER X-ray facility a prototype of a novel X-ray polarimetric telescope, using a Gas Pixel Detector (GPD) with polarimetric capabilities in the focal plane of the FM2. The GPD was developed by a collaboration between INFN-Pisa and INAF-IAPS. In the first phase of the test campaign, we have re-tested the FM2 at PANTER to have an up-to-date characterization in terms of angular resolution and effective area, while in the second part of the test the GPD has been placed in the focal plane of the FM2. In this paper we report the results of the tests of the sole FM2, using an unpolarized X-ray source, comparing the results with the calibration done in 1996.

Alignment of eROSITA like mirrors at the PANTER x-ray test facility

The development and calibration of eROSITA mirror modules is supported by continuous measurements at the X-ray test facility PANTER. To obtain comparable measurement results after each new integration robust alignment procedures are needed to place the mirror module on the optical axis. Here we present the different methods that we use to align eROSITA like mirror modules. One method uses the symmetry of single reflection images, another one is based on a symmetry of the intensity distribution, and the last one on the symmetry of the half energy width (HEW).