ASTRO-E2 precollimator for stray light protection: II. Fabrication and x-ray calibration

Details ASTRO-E2 precollimator for stray light protection: II. Fabrication and x-ray calibration ASTRO-E2 precollimator for stray light protection: II. Fabrication and x-ray calibration

Mar 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003spie.4851..750m&link_type=abstract

X-Ray and Gamma-Ray Telescopes and Instruments for Astronomy. Edited by Joachim E. Truemper, Harvey D. Tananbaum. Proceedings

Astronomy and Astrophysics

Astronomy

1

Scientific paper

ASTRO-E2 XRTs adopt Wolter Type-I optics and have nested thin foil structure to enhance their throughput. But this structure allows stray X-rays to come from the sky out of the XRT field of view. Stray light contaminates focal plane images, especially in the case of extended source observations. We intend to mount pre-collimators on top of the ASTRO-E2 XRTs to intercept stray light. On the other hand, reflection by the pre-collimator itself newly creates secondary stray light. To decrease these additional stray light as possible, the mil finish aluminium with its roller mark normal to the incident X-ray beam has been used for the slat material, whose reflectivity is reduced down to 1/20 of ideal specular reflection. Optical profilers tell us these samples have very rough surfaces, whose height varies with Σ = 1-2 μm. According to the design parameters as are described in the related paper in this symposium (Paper I), an engineering model pre-collimator is fabricated with 46 slats out of 175. Before EM pre-collimator is mounted onto XRT, alignment plates are adjusted to align slats to the same position of XRT primary reflectors. In x-ray measurements, stray light images and the flux of each stray light component at 30' off axis are measured with/without EM pre-collimator. The secondary only reflection component is reduced down to 3.6%, and the backside reflection component becomes more remarkable. On the other hand, X-ray measurement of the effective area at on axis with/without EM pre-collimator verifies that pre-collimator does not interfere the telescope aperture. In addition, the decrease of XRT field of view is ~10%, which is the same as the ray-tracing simulations. As a whole, EM pre-collimator reduces stray light to 27% level with only ~10% decrease of the XRT F.O.V.

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