Design, implementation, and performance of the Astro-H soft x-ray spectrometer aperture assembly and blocking filters

Abstract

The calorimeter array of the JAXA Astro-H (renamed Hitomi) soft x-ray spectrometer (SXS) was designed to provide unprecedented spectral resolution of spatially extended cosmic x-ray sources and of all cosmic x-ray sources in the Fe-K band around 6 keV. The properties that made the SXS array a powerful x-ray spectrometer also made it sensitive to photons from the entire electromagnetic band as well as particles. If characterized as a bolometer, it would have had a noise equivalent power of <4 × 10 −18 W∕ðHzÞ 0.5 . Thus, it was imperative to shield the detector from thermal radiation from the instrument and optical and UV photons from the sky. In addition, it was necessary to shield the coldest stages of the instrument from the thermal radiation emanating from the warmer stages. These needs were addressed by a series of five thin-film radiation-blocking filters, anchored to the nested temperature stages, that blocked long-wavelength radiation while minimizing x-ray attenuation. The aperture assembly was a system of barriers, baffles, filter carriers, and filter mounts that supported the filters and inhibited their potential contamination. The three outer filters also had been equipped with thermometers and heaters for decontamination. We present the requirements, design, implementation, and performance of the SXS aperture assembly and blocking filters. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Ground calibration of the Astro-H (Hitomi) soft x-ray spectrometer

“…The aperture assembly and filters are described in Ref. 7. The SXT image was sufficiently out of focus at the mesh filters-the beam from a point-source fills ∼9 mm of the 18.5-mm filter diameter for the IVCS filter-that our aim was to provide a best estimate of the spatially averaged total transmission rather than a twodimensional map.…”

“…The filters shield the detector from longwavelength thermal radiation from the instrument and optical and UV photons from the sky while allowing transmission in the soft x-ray waveband. 7 The mission goals required a careful calibration of the SXS components prior to launch. In this article, we describe the calibration approach and ground calibration measurements: Sec.…”

Ground test results of the electromagnetic interference for the x-ray microcalorimeter onboard XRISM

“…4.2), is larger by many orders than the x-ray input from the same direction during observations of O(1 fW) for a milli-Crab source. The microcalorimeter is protected against the input in electromagnetic forms of longer wavelengths than x-rays by the multiple layers of thin filters made of aluminized polyimide in the x-ray aperture 32 . For RF input, the Al in the filters of a 50- to 100-nm thickness reflects back most of the incoming power at its surface by the impedance mismatch with the vacuum, allowing only a small fraction (<−50 dB) to penetrate.…”

“…The microcalorimeter is protected against the input in electromagnetic forms of longer wavelengths than x-rays by the multiple layers of thin filters made of aluminized polyimide in the x-ray aperture. 32 For RF input, the Al in the filters of a 50-to 100-nm thickness reflects back most of the incoming power at its surface by the impedance mismatch with the vacuum, allowing only a small fraction (< − 50 dB) to penetrate. We speculate that multiple layers of such filters work effectively to reject RF noise input.…”

Lynx x-ray microcalorimeter cryogenic system

“…At the bottom of the cryostat, there is a gate valve and an aperture assembly to enable x-rays to directly pass through to the microcalorimeters while incorporating thin-film filters, similar to those on Hitomi, to block infrared and optical photons. 6 A detailed description of the aperture assembly and the filters is described elsewhere. 7 Outside of the gate valve, the LXM also includes an external filter wheel and a modulated x-ray source that is capable of providing pulsed x-ray lines at multiple energies and is similar to that used on Athena's X-IFU 5 and Hitomi's SXS 8 for in-flight calibration.…”