powerlaw, zpowerlw: power law photon spectrum

powerlaw is a simple photon power law. The zpowerlw variant computes a redshifted spectrum.

where:

par1 | , photon index of power law (dimensionless) |

norm | , photons/keV/cm/s at 1 keV |

For zpowerlw the formula and corresponding parameters are:

where:

par1 | , photon index of power law (dimensionless) |

par2 | , redshift |

norm | , 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.