get_backscal

Context: data

Synopsis

Return the source or background extraction region area

Syntax

get_backscal( [id, bkg_id] )

The get_backscal() function returns the extraction region area of a source or background PHA dataset by data id or bkg_id. The 'backscale' can be defined as the ratio of the area of the source (or background) extraction region in image pixels to the total number of image pixels. The fact that there is no ironclad definition for this quantity does not matter so long as the backscale for a source data set and its associated background data set are defined in the similar manner, because only the ratio of source and background backscale is used in analyses.

id - the id of the data set to use; if not given, uses the default dataset id (id=1 by default, see "ahelp get_default_id")
bkg_id - the id of the background to use; default=None

Example 1

sherpa> get_backscal()

When called with no arguments, get_backscal() returns the extraction region area of the source in the default data set.

sherpa> get_backscal()
           9.3626757073098007e-05

Example 2

sherpa> get_backscal(id=2, bkg_id=1)

To return the extraction region area of a background associated with a source data set, the data set ID and background ID must be supplied to get_backscal().

sherpa> get_backscal(2, 1)
           1.872535141462e-05

Bugs

See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.