Calibration Access and Data Handbook
Currently not used in the SAS, but may be in the future.
Is a placeholder that was supposed to have either some real background spectra
or some coefficients with which to generate background spectra.
It is currently not used, however might by used for a future
task that takes as input some proxies like the RA & Dec, the ROSAT broad
band count rates for the target location, the corner count rates etc.
and generates a best guess background file.