Calibration sources and filters of the soft x-ray spectrometer instrument on the Hitomi spacecraft

Abstract

Abstract. The soft x-ray spectrometer was designed to operate onboard the Japanese Hitomi (ASTRO-H) satellite. In the beam of this instrument, there was a filter wheel containing x-ray filters and active calibration sources. This paper describes this filter wheel. We show the purpose of the filters and the preflight calibrations performed. In addition, we present the calibration source design and measured performance. Finally, we conclude with prospects for future missions.

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

“…The SXS had a filter wheel (FW) between the telescope and dewar aperture. 25 The wheel had six positions, which included two open positions. Table 6 shows an overview of the FW filters.…”

“…Following damage to these calibrated flight-candidate filters in subsequent vibration tests, an uncalibrated qualification model Be filter was installed in the SXS FW. 25 The calibrated and uncalibrated filters were produced in the same batch and thus the material composition was likely to be the same, so we assumed the mass attenuation coefficients derived from the BESSY measurements remained valid. We also used the Be calibration results as a guide to the likely filter uniformity and thickness of the uncalibrated filter installed for flight.…”

“…There were two methods for flood-illuminating the array once the instrument was on the spacecraft, when we no longer were allowed to mount calibration equipment above the dewar. These onboard sources 25,37 could be used to check for or monitor offsets in gain between the calibration pixel and individual array pixels, as well as to monitor the spectral resolution of each pixel. First, there were the FW 55 Fe sources mounted on a metal structure that could be rotated into the optical path to illuminate the array.…”

In-orbit operation of the soft x-ray spectrometer onboard the Hitomi satellite

“…4) in order to aid in planning for future microcalorimeter missions. Details are found in other articles of the same special section for the spacecraft, 1 the overall mission instrument, 2 the sensor and its performance, [8][9][10][11] the mirror and the aperture assembly, 12,13 the cooling chain, 5,14-17 the vibration isolation system, 18 the filter wheel (FW), 4 and the signal processing. 19,20 All data presented here are available in Ref.…”

“…The commissioning of the instrument was planned to be completed in April 2016. The major remaining activities included opening of the Dewar gate valve (GV), the use and tuning of the modulated x-ray source (MXS), 4 and adjustment of the event threshold. Cryogen-free operation 5 was not tested in orbit, since its use was planned for years into the mission after the liquid helium was expended.…”