sherpa.astro.ui.fit_bkg(id=None, *otherids, **kwargs)

Fit a model to one or more background PHA data sets.

Fit only the backgound components of PHA data sets. This can be used to find the best-fit background parameters, which can then be frozen before fitting the data, or to ensure that these parameters are well defined before performing a simultaneous source and background fit.

  • id (int or str, optional) – The data set that provides the background data. If not given then all data sets with an associated background model are fit simultaneously.

  • *otherids (sequence of int or str, optional) – Other data sets to use in the calculation.

  • outfile (str, optional) – If set, then the fit results will be written to a file with this name. The file contains the per-iteration fit results.

  • clobber (bool, optional) – This flag controls whether an existing file can be overwritten (True) or if it raises an exception (False, the default setting).


sherpa.utils.err.FitErr – If filename already exists and clobber is False.


This is only for PHA data sets where the background is being modelled, rather than subtracted from the data.


Simultaneously fit all background data sets with models and then store the results in the variable fres:

>>> fit_bkg()
>>> fres = get_fit_results()

Fit the background for data sets 1 and 2, then do a simultaneous fit to the source and background data sets:

>>> fit_bkg(1, 2)
>>> fit(1, 2)