The in-flight spectroscopic performance of the Swift XRT CCD camera
  The Swift X-ray Telescope (XRT) focal plane camera is a front-illuminated MOS CCD, providing a spectral response kernel of 144 eV FWHM at 6.5 keV. We describe the CCD calibration program based on celestial and on-board calibration sources, relevant in-flight experiences, and developments in the CCD response model. We illustrate how the revised response model describes the calibration sources well. Loss of temperature control motivated a laboratory program to re-optimize the CCD substrate voltage, we describe the small changes in the CCD response that would result from use of a substrate voltage of 6V. 
J. P. Osborne, A. P. Beardmore, O. Godet, A. F. Abbey, M. R. Goad, K.   L. Page, A. A. Wells, L Angelini, D. N. Burrows, S. ...