Modeling the spectral response for the soft X-ray imager onboard the ASTRO-H satellite
Modeling the spectral response for the soft X-ray imager onboard the ASTRO-H satellite
复制标题
对 ASTRO-H 卫星上的软 X 射线成像仪的光谱响应进行建模
DOI：
10.1016/j.nima.2016.03.071
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
et al.
中科院分区：
文献类型：
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作者：
Shota Inoue;Kiyoshi Hayashida;Shuhei Katada;Hiroshi Nakajima;Ryo Nagino;Naohisa Anabuki;Hiroshi Tsunemi;and Shutaro Ueda;et al.
ASTRO-H卫星是日本第六颗X射线天文观测卫星，将于2016年初发射。该卫星携带四种探测器，其中之一是安装在X射线望远镜焦平面上的X射线CCD相机，即软X射线成像仪（SXI）。SXI包含四个CCD芯片，每个芯片的成像面积为31 mm× 31 mm，以马赛克方式排列，覆盖38′× 38′的视场，这是有史以来在轨道上飞行的最宽视场。CCD为P沟道背照式（BI）型，耗尽层厚度为200 μ m。我们在光子计数模式下操作CCD，其中每个光子的位置和能量在0.4-12 keV的能带中测量。为了评估用SXI获得的X射线光谱，其响应函数的准确校准是必不可少的。为此，我们在京都和KEK的光子工厂进行了校准实验，每个实验都使用具有各种X射线能量的不同X射线源。我们用5个分量拟合得到的光谱;主峰、次峰、恒定尾、Si逃逸和Si荧光，然后使用基于物理或经验的公式来建模它们的能量依赖性。由于这是首次在X射线天文卫星上采用P沟道BI型CCD，因此需要特别注意部分电荷收集产生的恒定尾部分量。结果发现，我们需要假设一个陷阱层在入射面的CCD和实现它的响应模型。此外，与前照式CCD相比，SXI响应的Si荧光分量明显较弱。
The ASTRO-H satellite is the 6th Japanese X-ray astronomical observatory to be launched in early 2016. The satellite carries four kinds of detectors, and one of them is an X-ray CCD camera, the soft X-ray imager (SXI), installed on the focal plane of an X-ray telescope. The SXI contains four CCD chips, each with an imaging area of 31 mm× 31 mm, arrayed in mosaic, covering the field-of-view of 38′× 38′, the widest ever flown in orbit. The CCDs are a P-channel back-illuminated (BI) type with a depletion layer thickness of 200 μ m. We operate the CCDs in a photon counting mode in which the position and energy of each photon are measured in the energy band of 0.4–12 keV. To evaluate the X-ray spectra obtained with the SXI, an accurate calibration of its response function is essential. For this purpose, we performed calibration experiments at Kyoto and Photon Factory of KEK, each with different X-ray sources with various X-ray energies. We fit the obtained spectra with 5 components; primary peak, secondary peak, constant tail, Si escape and Si fluorescence, and then model their energy dependence using physics-based or empirical formulae. Since this is the first adoption of P-channel BI-type CCDs on an X-ray astronomical satellite, we need to take special care on the constant tail component which is originated in partial charge collection. It is found that we need to assume a trapping layer at the incident surface of the CCD and implement it in the response model. In addition, the Si fluorescence component of the SXI response is significantly weak, compared with those of front-illuminated type CCDs.