Makoto Shouho

Soft x-ray response of the prototype CCD camera (XIS) for Astro-E

The x-ray imaging spectrometers (XIS) are x-ray CCD cameras on-board the Astro-E satellite launched in 2000. The XIS consists of 4 cameras, each of them will be installed on a focal plane of the Astro-E X-ray Telescope (XRT). The XIS not only have a higher sensitivity, which comes from a larger effective area of the XRT and thicker depletion layers of the XIS CCDs, than ASCA SIS. But also have several features that will overcome the radiation damage effects anticipated in the orbit. The calibration experiment at Osaka focuses on the soft x-ray response of the XIS. The calibration system employs a grating spectrometer which irradiates the CCD with dispersed x-rays. We have obtained preliminary results on the XIS proto model, including the energy-pulse-height relation, the energy-resolution relation, and the quantum efficiency at the energy range of 0.25-2.2 keV.

X-ray imaging spectrometers for Astro-E: ground calibration in the soft x-ray range

Soft X-ray response of X-ray Imaging Spectrometers (XIS) for the Astro-E satellite is measured with a grating spectrometer system at Osaka. First, relation between incident X-ray energy and output pulse height peak (E-PH relation) is examined with an SX grating. It is found that jump in the E-PH relation around Si-K edge is at most 2.7 eV. Second, quantum efficiency (QE) of the XIS in 0.4 - 2.2 keV range is measured relatively to the reference CCD of which absolute QE was calibrated with a gas proportional counter. The QE is fitted with a model in which CCD gate structures are considered. Systematic error on the QE results is estimated by referring an independent measurement. Third, tuning and improvement of the response function is performed. We employ six components to reproduce the response profile of the XIS. In this paper, improvement of one component which is originated in the events absorbed in the channel-stop is presented. Nevertheless, Astro-E was lost due to the launch failure. We overview the XIS project in its flight model phase, modified points of the design, problems and solutions etc., in order to be utilized in a possible recovery of the satellite.

Soft X-ray response of a CCD with a grating spectrometer

Abstract We calibrate the X-ray imaging spectrometers, which are CCD cameras installed on the ASTRO-E satellite, by using dispersed continuous soft X-rays from a grating spectrometer. We obtained the signal-pulse height and energy-resolution as a function of X-ray energies continuously. However, the wings of the line spread function of the grating distorts the center of the signal-pulse height derived by a simple analysis. An estimation of this distortion is presented. We also describe two methods of extracting the pure signal-pulse-height distribution from the data using the spectrometer. A brief description of the low-energy tail is presented.

Quantum efficiency of the CCD camera (XIS) for the ASTRO-E mission

We measured the optical and the X-ray transmission of the optical blocking filters for the X-ray Imaging Spectrometers (XISs) which are the X-ray CCD cameras of the ASTRO-E satellite. We conclude that the oxidation of the aluminum reduces the optical transmission down to ∼60–70% of the theoretical value of the aluminum. We achieved optical transmission below 5×10−5 in the range from 4000 to 9500 A by using aluminum thickness of 1200 A, while the theoretical calculation requires 800 A. The measurement of absolute quantum efficiency of XIS is also performed at several particular energies. We confirmed 20% quantum efficiency at 0.5 keV for the XIS engineering model (XIS EM).

Characteristics around oxygen and silicon K absorption edges of a charge-coupled device

We measure various spectral response characteristics around the oxygen and silicon K absorption edges of a Charge- Coupled Device X-ray detector used in the X-ray Imaging Spectrometer developed for the ASTRO-E mission. We have evaluated X-ray Absorption Fine Structure (XAFS) around oxygen K edge in detail. A strong absorption peak of 45% is confirmed just above the oxygen K edge and an oscillatory structure follows whose amplitude decreases from 20% at the edge to less than 1% at 0.9 keV. We also show XAFS and discuss on a change of the response function around the silicon K edge. The discontinuity of the signal pulse height at the silicon K edge is less than 1.8 eV. We determine the thickness of silicon, silicon dioxide, and silicon nitride in the dead layer using the depth of the absorption edge.

Reports of soft X-ray response of the engineering model of the CCD camera (XIS) for the ASTRO-E mission

Abstract XIS (X-ray Imaging Spectrometers) are four sets of X-ray CCD cameras, installed on the focal plane of the X-ray telescopes of ASTRO-E satellite, which will be launched in February, 2000. We have been calibrating the low energy (0.25-2.2 keV) response of the XIS using a spectrometer system in Osaka University. In this paper, we report the results of the calibration of the XIS EM (Engineering Model). We confirmed the energy resolution is about 130 eV at 5.9 keV (FWHM) and readout noise is ∼ 3–4 electrons (rms) at −90°C. And we measured the XIS response and energy resolution as a function of incident X-ray energy from 0.25 keV to 2.2 keV almost continuously, and absolute quantum efficiency. Based on the procedure we established, we are going to calibrate the XIS FM (Flight Model) which starts from August, 1998.

Properties of the optical blocking filter of the XIS for the ASTRO-E mission

Abstract The optical and X-ray transmission of the test samples of optical blocking filters (OBF) for the XIS (X-ray Imaging Spectrometer; CCD camera onboard the ASTRO-E satellite) were measured. Unexpected high transmission of optical lights was found. The oxidation of the aluminum layer is one possible cause of the high optical transmission.

Calibration of the X-ray CCD camera (XIS) for the ASTRO-E in the soft-x-ray band

The ASTRO-E X-ray Imaging Spectrometers (XISs) consists of four sets of X-ray CCD camera for the ASTRO-E mission. The XISs have been calibrated at Osaka University, Kyoto University, ISAS and MIT. The calibration experiment at Osaka focuses on the soft x-ray response of the XIS. The calibration of the XIS flight model has been performed since August 1998. We measured the signal-pulse height, the energy resolution and the quantum efficiency of the XIS as a function of energy, all of which are essential to construct the response function of the XIS. The detailed shape of the pulse-height-distribution are also investigated. We also constructed a numerical simulator of the XIS, which tracks the physical process in the CCD so as to reproduce the measured data. With a help of this simulator, we propose a model of the pulse-height-distribution of the XIS for single energy incident x-rays. The model consists of four components; two Gaussians, a constant, plus a triangle-shape component.

Quantum efficiency measurement of the x-ray CCD camera (XIS) for the ASTRO-E mission in the soft-x-ray band

We report the x-ray quantum efficiency of the XIS in the soft x-ray band between 0.5 keV and 2.2 keV. We also report the x-ray and optical transmission of the OBF. We obtained the quantum efficiency of the XIS of approximately 0.25 at 0.53 keV. We also obtained the x-ray transmission of approximately 0.65 at O K(alpha) and optical transmission below 5 X 10-5 in the range 400-950 nm.

Soft X-ray response of the CCD camera (XIS)

Soft X-ray response of the CCD camera (XIS, X-ray Imaging Spectrometer), which will be aboard the Astro-E satellite, was investigated for the monochromatic X-rays in the 0.25-2.2 keV. Detailed pulse-height distribution was examined particularly for O-K line, where significant low-energy tail was found. With the aid of Monte Carlo simulation we found that the photons absorbed in the channel stop was responsible for the component.