20 research outputs found
A wide field X-ray telescope for astronomical survey purposes: from theory to practice
X-ray mirrors are usually built in the Wolter I (paraboloid-hyperboloid)
configuration. This design exhibits no spherical aberration on-axis but suffers
from field curvature, coma and astigmatism, therefore the angular resolution
degrades rapidly with increasing off-axis angles. Different mirror designs
exist in which the primary and secondary mirror profiles are expanded as a
power series in order to increase the angular resolution at large off-axis
positions, at the expanses of the on-axis performances. Here we present the
design and global trade off study of an X-ray mirror systems based on
polynomial optics in view of the Wide Field X-ray Telescope (WFXT) mission.
WFXT aims at performing an extended cosmological survey in the soft X-ray band
with unprecedented flux sensitivity. To achieve these goals the angular
resolution required for the mission is very demanding ~5 arcsec mean resolution
across a 1-deg field of view. In addition an effective area of 5-9000 cm^2 at 1
keV is needed.Comment: Accepted for publication in the MNRAS (11pages, 3 table, 13 figures
Cold shaping of thin glass foils: a fast and cost-effective solution for making light-weight astronomical x-ray optics
Recent advancements in thin glass materials allowed the development and the mass production of very thin glass foils, like e.g. the Willow glass (thickness of 0.1-0.2 mm) produced by Corning or AF32 produced by Schott (thickness down to 0.055 mm). The thickness, strength and flexibility of these glass foils allow bending them up to very small radius of curvature without breaks. This feature, together with the very low micro-roughness, makes this kind of materials ideal candidates for pursuing a cold replication approach for cost-effective and fast making of grazing incidence astronomical optics. Starting from the very thin flat glass sheets, the process under development foresees to bond them onto the supporting structure while they are wrapped around reference mandrels. The assembly concept, based on the use of Wolter-I counter-form moulds, is also based on the use of reinforcing ribs that connect pairs of consecutive foils in the final assembly. The ribs do not only play the role of mechanical connectors, they keep the shape and increase the structural stiffness. Indeed, the ribs constrain the foil profile to the correct shape during the bonding, damping the low-frequency residuals with respect to the Wolter I configuration. This approach is particularly interesting because of their low weight and cost. They could e.g be used for the production of high throughput optics as those needed for the Chines XTP mission, in which the requirements on the angular resolution are not too tight. In fact, a Half Energy Width in the range of 20-60 arcsec is compatible with the expected residual error due to the spring back of the glass sheets. In this paper we provide an overview of the project, the expected performances and present the first preliminary results
Ion beam figuring technique used as final step in the manufacturing of the optics for the E-ELT
The INAF-Astronomical Observatory of Brera (INAF-OAB) is exploring the technical problems related to the ion beam figuring (IBF) of the Zerodur hexagonal mirrors (1.45 m corner to corner) of M1 for the European Extremely Large Telescope (E-ELT). As starting step a scaled down version mirror of the same material having size of 1 m corner to corner has been used to assess the relevant figuring problems. This specific mirror is spherical and has a radius of curvature of 3 m which allows a simple interferometric measurement setup. A mechanical support was designed to minimize its deformations due to gravity. The Ion Beam Figuring Facility used for this study has been recently completed in the Brera Observatory and has a figuring area of 170 cm x 140 cm. Aim of this study is the estimation and optimization of the time requested for the correction of the surface using also strategies to control the well-known thermal problems related to the Zerodur material. In this paper we report the results obtained figuring the 1 m corner-to-corner test segment
An X-ray Polarimeter for HXMT Mission
The development of micropixel gas detectors, capable to image tracks produced
in a gas by photoelectrons, makes possible to perform polarimetry of X-ray
celestial sources in the focus of grazing incidence X-ray telescopes. HXMT is a
mission by the Chinese Space Agency aimed to survey the Hard X-ray Sky with
Phoswich detectors, by exploitation of the direct demodulation technique. Since
a fraction of the HXMT time will be spent on dedicated pointing of particular
sources, it could host, with moderate additional resources a pair of X-ray
telescopes, each with a photoelectric X-ray polarimeter in the focal plane. We
present the design of the telescopes and the focal plane instrumentation and
discuss the performance of this instrument to detect the degree and angle of
linear polarization of some representative sources. Notwithstanding the limited
resources the proposed instrument can represent a breakthrough in X-ray
Polarimetry.Comment: 10 pages, 9 figure
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-gamma 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.Comment: Author's accepted manuscript posted to arXiv.org as permitted by
Springer's Self-Archiving Policy. The final publication is available at
http://rd.springer.com/article/10.1007%2Fs10686-013-9365-
An X-ray polarimeter for hard X-ray optics
Development of multi-layer optics makes feasible the use of X-ray telescope
at energy up to 60-80 keV: in this paper we discuss the extension of
photoelectric polarimeter based on Micro Pattern Gas Chamber to high energy
X-rays. We calculated the sensitivity with Neon and Argon based mixtures at
high pressure with thick absorption gap: placing the MPGC at focus of a next
generation multi-layer optics, galatic and extragalactic X-ray polarimetry can
be done up till 30 keV.Comment: 12 pages, 7 figure
POLARIX: a pathfinder mission of X-ray polarimetry
Since the birth of X-ray astronomy, spectral, spatial and timing observation
improved dramatically, procuring a wealth of information on the majority of the
classes of the celestial sources. Polarimetry, instead, remained basically
unprobed. X-ray polarimetry promises to provide additional information
procuring two new observable quantities, the degree and the angle of
polarization. POLARIX is a mission dedicated to X-ray polarimetry. It exploits
the polarimetric response of a Gas Pixel Detector, combined with position
sensitivity, that, at the focus of a telescope, results in a huge increase of
sensitivity. Three Gas Pixel Detectors are coupled with three X-ray optics
which are the heritage of JET-X mission. POLARIX will measure time resolved
X-ray polarization with an angular resolution of about 20 arcsec in a field of
view of 15 arcmin 15 arcmin and with an energy resolution of 20 % at 6
keV. The Minimum Detectable Polarization is 12 % for a source having a flux of
1 mCrab and 10^5 s of observing time. The satellite will be placed in an
equatorial orbit of 505 km of altitude by a Vega launcher.The telemetry
down-link station will be Malindi. The pointing of POLARIX satellite will be
gyroless and it will perform a double pointing during the earth occultation of
one source, so maximizing the scientific return. POLARIX data are for 75 % open
to the community while 25 % + SVP (Science Verification Phase, 1 month of
operation) is dedicated to a core program activity open to the contribution of
associated scientists. The planned duration of the mission is one year plus
three months of commissioning and SVP, suitable to perform most of the basic
science within the reach of this instrument.Comment: 42 pages, 28 figure
Technologies for the fabrication of the E-ELT mirrors within the T-REX project
With its primary mirror with 39 m of diameter, the E-ELT will be the largest optical/near-infrared telescope in the world and will gather 13 times more light than the largest optical telescopes existing today. The different optical sub-systems of E-ELT, including the primary mirror based on hundreds of reflecting tiles assembled together, represent key components for the implementation of the telescopes. A huge amount of aspherical reflecting elements have to be produced with "state of the art" figuring and polishing technologies and measured with proper metrological equipments. In the past couple of years, in the context of the T-REX project, a specific development program was carried out at the Brera Astronomical Observatory-INAF in order to address a numbers of technology aspects related to the fabrication of the E-ELT mirrors. In this paper we give a short overview of the activities that have been carried out. Other papers in this volume report on specific activities that have pursed within such a development program. skip=8p
POLARIX: a small mission of x-ray polarimetry
X-Ray Polarimetry can be now performed by using a Micro Pattern Gas Chamber
in the focus of a telescope. It requires large area optics for most important
scientific targets. But since the technique is additive a dedicated mission
with a cluster of small telescopes can perform many important measurements and
bridge the 40 year gap between OSO-8 data and future big telescopes such as
XEUS. POLARIX has been conceived as such a pathfinder. It is a Small Satellite
based on the optics of JET-X. Two telescopes are available in flight
configuration and three more can be easily produced starting from the available
superpolished mandrels. We show the capabilities of such a cluster of
telescopes each equipped with a focal plane photoelectric polarimeter and
discuss a few alternative solutions.Comment: 9 pages, 5 figure