2002 Chandra Calibration Workshop

Overview of the Pileup Model

In the HETGS pile-up model the predicted count rate is a non-linear function of the source flux. This can be seen in the following figure, which shows the predicted MEG first-order count-rate per frame as a function of the incident flux at 1 keV.

Figure showing flux vs count-rate in pileup model

Note that for small fluxes, the count-rate is proportional to the model. However, for larger fluxes, the non-linearity starts to manifest itself. At some critical flux, which will be called the saturation flux, the count-rate reaches a maximum value and then starts to decrease with increasing flux. Eventually the count-rate picks up again as events in the wings of the cross-dispersion profile become important.

See my 2002 SPIE paper for details of the the actual functional form of the relationship.

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This page was last updated Dec 16, 2002 by John E. Davis. To comment on it or the material presented here, send email to davis (at) space.mit.edu.