In-flight Calibration of the Hinode X-Ray Telescope: Correction for the Scattered Lights

The X-Ray Telescope (XRT) onboard Hinode has been observing the Sun in X-rays for more than a decade. In general, an astronomical telescope is designed to achieve the best image quality near the optical axis and, as a result, the optical performance gradually deteriorates away from the optical axis. XRT's field of view is 34x34 arc min and covers the full Sun, and the targets near the limb are always placed at the outskirt of the field of view. For this reason, the off-axis performance of XRT should be characterized carefully.

We have evaluated the amount of scattered light in the Hinode/XRT data by analyzing the in-flight images highly saturated during the solar flare events. It is revealed that, like the case of Yohkoh/SXT, the light scattered due to the roughness of mirror surface has a power-law distribution of r^-2 and also shows clear energy dependence, which has enabled us to complete a full description of XRT PSF profile from the core to the scattering wing. A successful restoration of the scattered light components in the observed XRT images will provide us with more precise information on the physical quantities of solar coronal plasma in the off-limb regions. Many interesting results on the correction for Hinode/XRT scattered light will be introduced and discussed thoroughly.