This task creates model particle background spectra and
images (if selected with a non-zero energy range) for the selected
region from the intermediate files produced from
pn-spectra.
The resultant image is in detector coordinates. The resultant image
is in detector coordinates which is transformed into sky coordinates
by the perl script
rot-im-det-sky.
pn_back
creates a QDP plot file which shows the source and model background
spectra for the observation. Any enhancement of the data over the
particle background model at higher energies probably indicates
residual soft proton contamination, unless there are really hard and
bright sources in the field.