set_bkg_full_model(id, model=None, bkg_id=None)¶
Define the convolved background model expression for a PHA data set.
Set a model expression for a background data set in the same way that set_full_model does for a source. This is for when the background is being fitted simultaneously to the source, rather than subtracted from it.
id (int or str, optional) – The data set containing the source expression. If not given then the default identifier is used, as returned by get_default_id.
model (str or sherpa.models.Model object) – This defines the model used to fit the data. It can be a Python expression or a string version of it.
bkg_id (int or str, optional) – The identifier for the background of the data set, in cases where multiple backgrounds are provided.
The function does not follow the normal Python standards for parameter use, since it is designed for easy interactive use. When called with a single un-named argument, it is taken to be the model parameter. If given two un-named arguments, then they are interpreted as the id and model parameters, respectively.
Some functions - such as plot_bkg_source - may not work for model expressions created by set_bkg_full_model.
The background is fit by two power laws - one that is passed through the instrument response (
gbgnd) and one that is not (
pbgnd). The source is modelled by
xsphabs * galabs, together with the background model, scaled by the ratio of area and time. Note that the background component in the source expression uses the source response rather than background response.
>>> rsp = get_response() >>> bresp = get_response(bkg_id=1) >>> bscale = get_bkg_scale() >>> smodel = xsphabs.galabs * xsapec.emiss >>> bmdl = brsp(powlaw1d.gbdng) + powlaw1d.pbgnd >>> smdl = rsp(smodel) + bscale*(rsp(gbgnd) + pbgnd) >>> set_full_model(smdl) >>> set_bkg_full_model(bmdl)