Appendix J: Glossary

• Component - A part of a model.
  • Additive - A component which produces a theoretical spectrum.
  • Multiplicative - A component which produces multiplicative factors to apply to the current theoretical spectrum.
  • Convolution - A component which modifies the current theoretical spectrum
  • Mixing - If there are multiple datasets with separately calculated theoretical models this component modifies all of them simultaneously.
• Datagroup - A set of observed spectra which will all be fit using the same model and parameter values.
• Dataset - The observed spectrum and its associated information.
• Fit statistic - The statistic used to determine the best fit value. The options are based on maximizing the likelihood.
• Model - The parameterized theoretical model for the source spectrum. There is a default unnamed model but additional named models can be defined.
• Plotgroup - A set of spectra which are summed together for plotting purposes only.
• Response Model - A model which modifies the response. At the moment this is limited to the gain.
• Source - In some observations several objects can contribute to the same spectrum. In this case XSPEC refers to them as different sources and each source can have its own model and response.
• Table Model - A model component stored as a FITS file containing model spectra tabulated on a grid of parameter values.
• Test Statistic - The statistic to provide the goodness-of-fit criterion after the parameters have been optimized based on the fit statistic