If the number of net counts for a source is less than it is impractical to fit the data in all 34 energy bits. However, if the flux is required, then a fit must be performed first. This can be done by setting the hidden parameter rebin=yes, which bins the data into a single bin before fitting for the normalization only. The user must specify all the parameters in the chosen model except the normalization. Fit will then calculate the normalization of the model and xflux can be used to determine the flux and luminosity of the source from the best fit model.
xs> fit rebin=yes