Sets attributes of a background dataset.
sherpa> SETBACK [# [ID]] <arg> = <numeric>
where # specifies the number of the background dataset (default dataset
number is 1). The ID modifier is used if and only if the Sherpa state
object variable multiback is set to 1, i.e., if more than one
background dataset is to be associated with a single source dataset.
The ID modifier may be any unreserved string (e.g., A, foo, etc.),
i.e., a string that is not a parsable command.
The argument <arg> is one of the following options:
SETBACK Command Arguments
| BACKSCALE |
A normalizing quantity which can indicate the the ratio of the
area of the background extraction region in an image to the full image
area. |
| TIME |
The exposure time of the
background observation. |
The primary use of this command is to set the attributes of non-PHA
datasets (e.g., ASCII datasets). Setting TIME
affects the normalization of the background model, which is entered with
the BACKGROUND command.
Setting BACKSCAL affects the relative normalization
of the background model when it is applied to a source region.
For instance, if the background model amplitude in a background dataset bin is
M_B, the BACKSCAL of that dataset is
B_B, and the BACKSCAL of the source dataset
is B_S, then the contribution of the background to the
source region spectrum is
For related information, see SETDATA.
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