Further to the request from PR#90 we added a sample set of background files
based on SciSIM output. Note however the reply to PR#90 still applies,
i.e. QuickSIM does a better job of representing the galactic background 
variation with location, which is the major component.

The associated files here have been simulated using the broken power law
plus single temperature model similar to that of    Chen, Fabian and Gendreau.
A "typical galactic location" was adopted, and SciSIM ran without the large
radius really necessary	to account for (20% ?)	scattered X-rays from outside 
the field of view. 

The extracted PHA files represent the spectrum obtained from the whole
field of view after 50ksecs integration, so represents also the average
vignetting factor of the field.

We think it is probably not constructive to repeat this exercise for a large
range of conditions, extraction radii, etc etc., but provided them as a 
representative data set just to indicate the possibilities for simulations the 
user can perform.

Charged Particles
Note the simulation does not include effects of charged particle background.
This is expected to be a flat spectrum which dominates the X-ray diffuse
background for energies greater than about 5 - 7 keV. There will be variations
around the orbit and with solar flare conditions, while the PN camera will
probably have a factor ~2 higher background than the MOS due to a deeper
detection layer and enhanced sensitivity to local gammas.

Again there are so many variables and unknowns, providing a prescriptive
data set was felt to be too contentious.