The XSPEC implementation

To summarize the preceding section, the main components of spectral fitting are as follows:

1. The observed spectrum (C(I))
2. The instrumental response (R(I,E))
3. A model spectrum (f(E))

These components are used in the following manner:

1. A parameterized model is created that one feels represents the actual spectrum of the source.
2. One then gives values to the model parameters.
3. Based on the parameter values given, one predicts the count spectrum that would be detected by the spectrometer in a given channel for such a model.
4. Then, one compares the predicted spectrum to the spectrum actually obtained by the instrument.
5. The values of the parameters of the model are manipulated until one finds the best fit between the theoretical model and the observed data.
6. One then calculates the ``goodness" of the fit to determine how well the model explains the observed data, and calculates the confidence intervals for the model's parameters.

This section describes how XSPEC performs these tasks.

• C(I): The Observed Spectrum
• R(I,E): The Instrumental Response
• f(E): The Model Spectrum
• Fits and Confidence Intervals