get_bkg_scale¶

sherpa.astro.ui.get_bkg_scale(id=None)¶

Return the background scaling factor for a PHA data set.

Return the factor applied to the background component to scale it to match it to the source (either when subtracting the background, or fitting it simultaneously).

Parameters:	id (int or str, optional) – The identifier for the data set to use. If not given then the default identifier is used, as returned by get_default_id.
Returns:	ratio – The scaling factor. The result can vary per channel, in which case an array is returned.
Return type:	number or array

See also

get_areascal(): Return the fractional area factor of a PHA data set.
get_backscal(): Return the area scaling factor for a PHA data set.
set_backscal(): Change the area scaling of a PHA data set.
set_full_model(): Define the convolved model expression for a data set.
set_bkg_full_model(): Define the convolved background model expression for a PHA data set.

Notes

The scale factor:

exp_src * bscale_src / (exp_bgnd * bscale_bgnd)

where exp_x and bscale_x are the exposure and BACKSCAL values for the source (x=src) and background (x=bgnd) regions, respectively.

Examples

>>> get_bkg_scale('pi')
0.034514770047217924