Direct measurement of sub-pixel structure of the EPIC MOS CCD on-board theXMM/NEWTON satellite

We have used a mesh experiment in order to measure the: sub-pixel structure of the EPIC MOS CCDs on-board the XMM/NEWTON satellite. The EPIC MOS CCDs have 40 mum-square pixels which have tin open electrode structure in order to improve the detection efficiency for low-energy X-rays. We obtained rest ored pixel images for various X-ray event grades (e.g. split-pixel events, single pixel events, etc.) at various X-ray energies. We confirmed that the open electrode structure results in a distorted horizontal pixel boundary. The open electrode region generates both single pixel events and verticall y split events, but no horizontally split events. Because the single pixel events usually show the best energy resolution, we discuss a method of incr easing the fraction of single pixel events from the open electrode region. Furthermore, we have directly measured the thickness of the electrodes and dead-layers by comparing spectra from the open electrode region with those from the other regions: electrodes. electrode finger and channel stop. We c an say that EPIC MOS CCDs are more radiation hard than front-illumination c hips of ACIS on-board Chandra X-ray Observatory because of their extra abso rption thickness above the charge transfer channel. We calculated the mean pixel response and found that our estimation has a good agreement with that of the ground calibration of EPIC MOS CCD. (C) 2001 Elsevier Science B.V. All rights reserved.