First light of BEaTriX, the new testing facility for the modular X-ray optics of the ATHENA mission

¹ Istituto Nazionale di Astrofisica (INAF), Osservatorio Astronomico di Brera (OAB), Via E. Bianchi 46, 23807 Merate, Italy
e-mail: daniele.spiga@inaf.it
² Politecnico Milano Bovisa, Via La Masa 34, 20156 Milano, Italy
³ IIS Bachelet, Via Stignani 63/65, 20081 Abbiategrasso, Milano, Italy
⁴ INAF - Istituto di Fisica Spaziale e Fisica cosmica Milano (IASF-Mi), Via A. Corti 12, 40133 Milano, Italy
⁵ INAF - Osservatorio Astronomico di Padova (OAPD), Vicolo Osservatorio 5, 35122 Padova, Italy
⁶ IMEM-CNR, Parco Area delle Scienze 37/A, 43124 Parma, Italy
⁷ European Synchrotron Radiation Facility, BP 220, 38043 Grenoble, France
⁸ BCV Progetti, Via S. Orsola 1, 20123 Milano, Italy
⁹ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstr, 85748 Garching Germany
¹⁰ DTU-space, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
¹¹ ESTEC, European Space Agency, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
¹² Cosine, Warmonderweg 14, 2171 AH Sassenheim, The Netherlands

Received: 15 May 2022
Accepted: 29 June 2022

Abstract

Aims. The Beam Expander Testing X-ray facility (BEaTriX) is a unique X-ray apparatus now operated at the Istituto Nazionale di Astrofisica (INAF), Osservatorio Astronomico di Brera (OAB), in Merate, Italy. It has been specifically designed to measure the point spread function (PSF) and the effective area (EA) of the X-ray mirror modules (MMs) of the Advanced Telescope for High-ENergy Astrophysics (ATHENA), based on silicon pore optics (SPO) technology, for verification before integration into the mirror assembly. To this end, BEaTriX generates a broad, uniform, monochromatic, and collimated X-ray beam at 4.51 keV. The beam collimation is better than a few arcseconds, ensuring reliable tests of the ATHENA MMs, in their focus at a 12 m distance.

Methods. In BEaTriX, a micro-focus X-ray source with a titanium anode is placed in the focus of a paraboloidal mirror, which generates a parallel beam. A crystal monochromator selects the 4.51 keV line, which is expanded to the final size by a crystal asymmetrically cut with respect to the crystalline planes. An in-house-built Hartmann plate was used to characterize the X-ray beam divergence, observing the deviation of X-ray beams from the nominal positions, on a 12-m-distant CCD camera. After characterization, the BEaTriX beam has the nominal dimensions of 170 mm × 60 mm, with a vertical divergence of 1.65 arcsec and a horizontal divergence varying between 2.7 and 3.45 arcsec, depending on the monochromator setting: either high collimation or high intensity. The flux per area unit varies from 10 to 50 photons s⁻¹ cm⁻² from one configuration to the other.

Results. The BEaTriX beam performance was tested using an SPO MM, whose entrance pupil was fully illuminated by the expanded beam, and its focus was directly imaged onto the camera. The first light test returned a PSF and an EA in full agreement with expectations. As of today, the 4.51 keV beamline of BEaTriX is operational and can characterize modular X-ray optics, measuring their PSF and EA with a typical exposure of 30 min. Another beamline at 1.49 keV is under development and will be integrated into the current equipment. We expect BEaTriX to be a crucial facility for the functional test of modular X-ray optics, such as the SPO MMs for ATHENA.