CCD pile-up model used for brightish point sources observed by Chandra. This is an implementation of the fast pile-up algorithm proposed by John Davis (see http://space.mit.edu/~davis/papers/pileup2001.pdf). The frame time and maximum number of photons to pile up should be fixed. The grade morphing is expressed through a single parameter, alpha, which should be left as a free parameter. This model should be considered in beta test. Note that to calculate fluxes etc. for the model you must remove the pileup component. The pile-up model is similar to the operation of the convolution models, differing only in the treatment of the detector efficiency during the convolution. Note that renorm will not work with pileup since increasing the normalization does not linearly increase the predicted count rate. Therefore you should set renorm none prior to doing a fit with pileup.
| par1 | frame time (in seconds) |
| par2 | maximum number of photons to pile up |
| par3 | grade correction for single photon detection |
| par4 | grade morphing parameter (good grade fraction is assumed proportional
to par4 where p is the number of piled photons) |
| par5 | PSF fraction. Only this fraction will be treated for pile-up. Note that this is not the fraction of the PSF included in the extraction region but is the fraction of counts in the region which are from the point source whose pile-up is being modeled. For this model to work well the extraction region should be large enough to contain essentially all the PSF. |
| par6 | Number of regions. The counts to be piled-up will be distributed among par6 regions, which will be piled-up independently. |
| par7 | Value of FRACEXPO keyword in ARF. |