Spectral re-distribution and surface loss effects in Swift XRT (XMM-Newton EPIC) MOS CCDs

In the course of testing and selecting the EPIC MOS CCDs for the XMM-Newton observatory, the authors developed a Monte-Carlo model of the CCD response. Among other things, this model was used to investigate surface loss effects evident at low energies. By fitting laboratory data, these losses were characterised as a simple function of X-ray interaction depth and this result enabled the spectral re-distribution itself to be modelled as a simple analytical function. Subsequently, this analytical function has been used to generate the response matrix for the EPIC MOS instruments and will now be employed to model the spectral re-distribution for the Swift XRT CCD.