Background radiation affects XMM-Newton observations
due to the large collecting area of its mirrors.
A proper background subtraction strategy allows to satisfy
the original scientific request for the large
majority of observations.
Scientists proposing observations aiming to detect faintest
point-like or extended sources at the technical limit of the
instruments, i.e. observations requiring a ``zero''
background radiation level, or observations
aiming variability studies, should propose an exposure
time increased by 40% with respect to the calculated value.
The feasibility study of extended sources requires special attention.
Proposers should consider that besides the X-ray background also
the instrumental background has to be taken into account.
Experience shows that in the absolute minimum
proposers should provide the background count rate per unit
area (count/s/cm
) and the signal to background
ratio required for
the most critical region, i.e. the region
for which the spectral analysis or deeper source detection
is proposed.
Proposers should also specify the energy
bands to which these numbers are referring.