Does BACKSCAL take into account
all the "blank areas" in a spectrum extraction region?
EPIC X-ray spectra are expressed
in counts per spectral channel. Spectral fitting programs
such as XSPEC apply the proper renormalization to
the background spectra, using the value of the BACKSCAL
keyword in the header of the spectral file(s). The
SAS task
backscale calculates the
BACKSCAL value.
backscale is automatically run, when a spectrum is extracted
via
xmmselect.
Users must be aware that the current implementation of
backscale employs the full area of the spectrum extraction region,
save the
(known) bad pixels/columns. Other effects, such as:
- the edge of the field of view
- windowing selections, e.g.
the reduced central CCD area in small window mode
- any CCD selection used while extracting the spectrum, e.g.
CCDNR==1
are also taken into account.
