Return the background ARF associated with a PHA data set.

This is for the case when there is only one background component and one background response. If this does not hold, use get_arf and use the bkg_id and resp_id arguments.

Parameters:id (int or str, optional) – The data set to use. If not given then the default identifier is used, as returned by get_default_id.
Returns:arf – This is a reference to the ARF, rather than a copy, so that changing the fields of the object will change the values in the data set.
Return type:a sherpa.astro.instrument.ARF1D instance

See also

Simulate a PHA data set from a model.
Load an ARF from a file and add it to the background of a PHA data set.
Load a file as a PHA data set.
Define the convolved model expression for a data set.
Set the ARF for use by a PHA data set.
Set the RMF for use by a PHA data set.
Read in an ARF from a file.


Return the exposure field of the ARF from the background of the default data set:

>>> get_bkg_arf().exposure

Copy the ARF from the default data set to data set 2, as the first component:

>>> arf1 = get_bkg_arf()
>>> set_arf(2, arf1, bkg_id=1)