backcorr
makes a background spectrum appropriate to the
accumulation region used for a given source spectrum. The task calls
arfgen
twice; once for the source region and once for the
background region. The regions are read directly from the input
datasets by
arfgen
. This gives the integrated effective area
as a function of energy over both regions. From these two effective
area curves, a direct normalization of the input background spectrum
is performed.