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The background properties of Suzaku/XIS

Suzaku is the fifth Japanese X-ray astronomical satellite and it was launched in July 2005. The Suzaku X-ray Imaging Spectrometers (XISs) consist of four X-ray Charge-Coupled Device (CCD) cameras. Three of them are front-illuminated (FI) CCD, and the other is back-illuminated (BI) CCD. The strong points of the XIS are a high energy resolution, a large effective area, and a low and stable background. In particular, the background level of the Suzaku/XIS is much lower than the other X-ray satellites, XMM-Newton/EPIC and Chandra/ACIS. We investigated the background property of the XIS using the data obtained when the satellite is looking at the night earth, and proved the low level and the stability of the XIS background. Non X-ray background (NXB) consists of continuum component and some emission lines. The continuum component is very different between the FI-CCD and the BI-CCD. We discussed the positional dependence of the continuum component and the line components, and proved that the flux of the line components of the NXB is higher in the frame-store region than the imaging area. Finally, we investigated the effects of magnetic cut-off rigidity (COR) upon the count rate of NXB.