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 |

par5 |
PSF fraction. Only this
fraction will be treated for pile-up. Note that this is |

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. |