XMM Users' Handbook

   
ESim - The EPIC Simulator

ESim simulates the properties of both types of EPIC cameras, MOS and pn.

The two camera types are fundamentally different, the MOS chips, e.g., being front-illuminated, while the pn CCDs are back-illuminated. ESim models the interaction of X-ray photons with the CCDs and records the results in output files. These output files contain event lists, as they would also be obtained during real observations in orbit.

ESim, as the other instrument simulators, is capable of simulating all science data acquisition modes of the detectors. Other parts of ESim simulate event recognition patterns etc., including parts of the XMM onboard software.

ESim currently comprises routines to model the following features:

• Camera selection (MOS vs. pn)

• Exposure time

• Position of camera with respect to the mirrors

• Full image mode

• Window mode

• CCD selection

• Dead space in between CCDs

• Simple dead front and partially absorbing back layers (limiting the low energy X-ray detection efficiency)

• Photon shot noise at interaction within the CCD

• Si-K $\alpha$ fluorescence

• Diffusion/drift of generated electrons through various layers in a CCD

• Recombination losses

• Spreading of an event over several pixels

• Frame time analysis

• Grading (event recognition)

• Threshold selection

• Dark noise

• Electronic noise

• Background subtraction

• ``Out of time'' events received during CCD readout