A BeppoSAX observation of the super-soft source CAL87

We report on a BeppoSAX Concentrator Spectrometer observation of the super-soft source (SSS) CAL87. The X-ray emission in SSS is believed to arise from nuclear burning of accreted material on the surface of a white dwarf (WD). An absorbed blackbody spectral model gives a chi^2_v of 1.18 and a temperature of 42 +/- ^13 _11 eV. However, the derived luminosity and radius are greater than the Eddington limit and radius of a WD. Including an O viii edge at 0.871 keV gives a significantly better fit (at > 95% confidence) and results in more realistic values of the source luminosity and radius. We also fit WD atmosphere models to the CAL87 spectrum. These also give reasonable bolometric luminosities and radii in the ranges 2.7-4.8 10^{36} erg/s and 8-20 10^7 cm, respectively. These results support the view that the X-ray emission from CAL87 results from nuclear burning in the atmosphere of a WD.Comment: 4 pages. Accepted for publication in A&A (Letters

Extreme Physics via X-rays from Black Holes and `Neutron' Stars

A combination of microchannel plate optics and a 32x32 pixel microcalorimeter would allow the successor to the Rossi XTE to explore new domains of spectroscopic timing in a MIDEX class mission. With ~10 times the area and ~100 times the spectral resolution of the PCA (and 10 times that of silicon detectors) such a mission would be able to explore redshifts and plasma conditions in weak line features over a wide range of celestial sources. This would allow several tests of basic physics, both QED/QCD and GR.Comment: 3 pages, 0 figures; for procedings of the `2nd International Conference on Particle and Fundamental Physics in Space

Optimization of grazing incidence mirrors and its application to surveying X-ray telescopes

Grazing incidence mirrors for X-ray astronomy are usually designed in the parabola-hyperbola (Wolter I) configuration. This design allows for optimal images on-axis, which however degrade rapidly with the off-axis angle. Mirror surfaces described by polynomia (with terms higher than order two), have been put forward to improve the performances over the field of view. Here we present a refined procedure aimed at optimizing wide-field grazing incidence telescopes for X-ray astronomy. We improve the angular resolution over existing (wide-field) designs by ~ 20%. We further consider the corrections for the different plate scale and focal plane curvature of the mirror shells, which sharpen by another ~ 20% the image quality. This results in a factor of ~ 2 reduction in the observing time needed to achieve the same sensitivity over existing wide-field designs and of ~ 5 over Wolter I telescopes. We demonstrate that such wide-field X-ray telescopes are highly advantageous for deep surveys of the X-ray sky.Comment: 8 pages 4 figures. Accepted for publication on A&A (macro included

BEaTriX, expanded x-ray beam facility for testing modular elements of telescope optics: an update

We present in this paper an update on the design of BEaTriX (Beam Expander Testing X-ray facility), an X-ray apparatus to be realized at INAF/OAB and that will generate an expanded, uniform and parallel beam of soft X-rays. BEaTriX will be used to perform the functional tests of X-ray focusing modules of large X-ray optics such as those for the ATHENA X-ray observatory, using the Silicon Pore Optics (SPO) as a baseline technology, and Slumped Glass Optics (SGO) as a possible alternative. Performing the tests in X-rays provides the advantage of an in-situ, at-wavelength quality control of the optical modules produced in series by the industry, performing a selection of the modules with the best angular resolution, and, in the case of SPOs, there is also the interesting possibility to align the parabolic and the hyperbolic stacks directly under X-rays, to minimize the aberrations. However, a parallel beam with divergence below 2 arcsec is necessary in order to measure mirror elements that are expected to reach an angular resolution of about 4 arcsec, since the ATHENA requirement for the entire telescope is 5 arcsec. Such a low divergence over the typical aperture of modular optics would require an X-ray source to be located in a several kilometers long vacuum tube. In contrast, BEaTriX will be compact enough (5 m x 14 m) to be housed in a small laboratory, will produce an expanded X-ray beam 60 mm x 200 mm broad, characterized by a very low divergence (1.5 arcsec HEW), strong polarization, high uniformity, and X-ray energy selectable between 1.5 keV and 4.5 keV. In this work we describe the BEaTriX layout and show a performance simulation for the X-ray energy of 4.5 keV

BEaTriX, the Beam Expander Testing X-ray facility for testing ATHENA's SPO modules: the collimating mirror

The BEaTriX (Beam Expander Testing X-ray) facility is now under construction at INAF-Brera Astronomical Observatory with the support of ESA. We aim to use it as a pathfinder to demonstrate the feasibility of the acceptance tests of the ATHENA’s Silicon pore optics Mirror Modules (MM), i.e., point spread function and effective area measurements at two energies for all MMs. A microfocus X-ray source placed in the focus of a paraboloid mirror will provide a collimated X-ray beam to the next stages featuring the facility, i.e., the monochromator and the beam expansion units, which will finally enable the full illumination of the mirror modules under test. The collimating mirror has to satisfy severe surface specifications to allow the divergence of the X-ray beam reaching the requirements. Simulations, based on physical optics, have shown that the optical quality of the mirror surface has to reach 0.5 arcsec Half-Energy Width (HEW) at 4.51 keV. We procured a ground and lapped mirror substrate in HOQ 310 fused quartz material. The first step of the process is based on the bonnet polishing technology with our CNC IRP1200 Zeeko machine, and it is guided by the analysis of the metrological data obtained by the optical profilometer present at Media Lario S.r.l. laboratories. The spatial frequency errors not correctable by bonnet polishing can be then removed by smoothing and superpolishing processes, followed by ion beam figuring to correct the remaining errors in the low frequency range. In this paper, we report on the analysis performed to correlate the requirement on beam divergence to the manufacturing tolerances on the surface. We present the manufacturing process and the results so far achieved