bkn2pow: broken power law, 2 break energies

A three-segment broken power law (i.e. with two break energies).

where:

par1 = | power law photon index for |

par2 = | first break point for the energy in keV |

par3 = | power law photon index for |

par4 = | second break point for the energy in keV |

par5 = | power law photon index for |

norm = K | photons/keV/cm/s at 1 keV |

If POW_EMIN and POW_EMAX have been defined by the xset command then the norm becomes the flux in units of ergs/cm/s over the energy range (POW_EMIN, POW_EMAX) keV unless POW_EMIN = POW_EMAX in which case the norm becomes the flux density in micro-Jansky at POW_EMIN keV. In these cases it is important that POW_EMIN and POW_EMAX lie within the energy range on which the model is being evaluated.