Define the form of the theoretical model to be fit to the data.
XSPEC> model [<delimeter>] <component1> <delimeter> <component2> <delimeter> ... <componentN> [<delimeter>]
where <delimeter> is some combination of (, +, *, ), and <componentJ> is one of the models known to XSPEC. Descriptions of these models may be accessed using the help model command. The models are divided into four types: additive, multiplicative, convolution and mixing models. Additive models are those directly associated with emissivity, such as power laws, thermal models, emission lines, etc. The net effect of two independent additive models is just the sum of their individual emissivities. Multiplicative models, on the other hand, do not directly produce photons, but instead modify (by an energy-dependent multiplicative parameter) the spectrum produced by one or more additive components. Examples of multiplicative models are photoelectric absorption models, edges, absorption lines, etc. Convolution models are like multiplicative models in that they modify the spectrum, but unlike multiplicative models they modify the spectrum as a whole, allowing for more complex operations than bin by bin multiplication factors. An example of a convolution model is a gaussian smoothing with energy dependent sigma. Note that when using convolution models, ordering of components may become significant. See under ``combination rules'' for a explanation of the order in which convolution and multiplicative models are applied.
Mixing models are a special case for multiple datagroups and mix the model up between the datagroups.
A list of all the currently installed models is given in response to the component ?. To remove the current model type model none. See the commands delcomp, addcomp and editmod for details on how to modify the current model without having to enter a completely new model.