Pile-up on X-ray CCD instruments

Abstract

Pile-up occurs on X-ray CCDs when several photons hit the detector at the same place between two readouts. In that case they are counted as one (or not at all) and their energies are summed. Pile-up thus affects both flux measurements and spectral characterisation of bright sources. Here I extend a previous work on flux loss, and present a simple formula for spectral distortion, in a form directly applicable when the pixel size is much smaller than the telescope's point spread function, but which can be extended to a more general case.