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Model Spectra for Spectral-Fitting Program

For on-line information type: cl> help using_spectral

The models provided are:

For detailed information on model parameters, please refer to the science specifications in xspectraldoc$spectral.(tex,dvi).

The spectral model and its parameters are passed to the fitting tasks as:


More than one absorption and more than one spectral model can be combined in the following ways:




Some basic rules for writing a model description:

NOTE: When different spectral models with different units for the normalization are combined, the relative normalization of the second model can be quite large.

For example: ray(1:2,c,100)+pow(11:13,1:2)

specifies a power-law model with a flux of approximately 1% of the flux in the Raymond model.

See cl> help models_spectral for more information on syntax.

Note: The program fit starts at the midpoint of the parameter range specified, then changes the parameters to determine the direction in which $\chi ^{2}$ is decreasing and heads in that direction to find the parameter values that give the minimum $\chi ^{2}$. If the initial parameter range is large, only part of the parameter space may be tested, and the program can settle into a secondary minimum. The real minimum can be missed. Choose parameter limits carefully.



to describe a power law model spectrum, with energy index varying between 1 and 2, and a galactic absorption varying between 1020 and 1021 cm-2.


for two power law models, and one absorption applied to both of them. The galactic absorption can vary between 1020 and 1021 cm-2, the intrinsic absorption is fixed at 1023, for an object at z=1. The energy index of the first power law model can vary between 1 and 2, with the best fit normalization calculated by the program. The second power law has a fixed index of 1.5, and its normalization is allowed to vary between 50 and 60 % of the first one.


to describe two power law models, each with galactic absorption in two different ranges.

next up previous contents
Next: Structure of the Spectral Up: Spectral Analysis Previous: Notes on IPC and