Model of the backside illuminated Chandra CCD

In this work we describe a simulator developed to model the x-ray response of the backside illuminated Chandra CCDs. The model is based on the Monte Carlo technique, where individual x-ray photons are thrown into the silicon structure and the behavior of the simulated electron clouds is calculated. In order to reproduce the complex redistribution function of the device at low energies we had to introduce charge losses for the clouds formed near the illuminated surface. An important feature of this model is its simulation of Charge Transfer Inefficiency (CTI) which attempts to reproduce losses of signal charge to electron traps in the buried channel of the device during different vertical and horizontal charge transfers. The CTI model takes into account a reduction of the number of empty traps in the channel due to precursor charge packets found in the previous rows of the image section of the device. Parameters of the model were tuned to fit the large amount of experimental data acquired during the on-the-ground calibration of the Chandra devices at energies ranging from 277 eV to 9.9 keV.