Restoring the Suzaku Source Position Accuracy and Point-Spread function

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Abstract We present an empirical correction of sky coordinates of X-ray photons obtained with the X-ray Imaging Spectrometer (XIS) aboard the Suzaku satellite to improve the source position accuracy and restore the point-spread function (PSF). The XIS images are known to have an uncertainty in position of up to $1′$, and to show considerable degradations of the PSF. These problems are caused by a drifting of the satellite attitude due to thermal distortion of the side panel #7, where the attitude control system is mounted. We found that the position error averaged over a pointing observation can be largely reduced by using the relation between the deviation of the source position in the DETX direction and the ecliptic latitude of the pointing target. We parameterized the wobbling of the source position synchronized with the 96-minute satellite orbital period with temperatures of onboard radiators and elapsed time since the night-day transition of the spacecraft. We developed software, aeattcor, to correct the image drift using these parameters, and applied it to 27 point-source images taken in the Suzaku initial science-operation phase. We show that the radius of the 90% error circle of the source position was reduced to $19′$ and the PSF was sharpened. These improvements have enhanced the scientific capability of the Suzaku XIS.