******* should be part of the user-supplied det-prep script??? But does not sensy need an estimate of the background?
This function may be performed alone by calling the script with entrystage and finalstage=`sensmaps'.
Theoretically, given an exposure map, a background map and a knowledge of the source detection algorithm, one ought to be able to calculate the sensitivity limit of the source detection algorithm at each point in the sky, in terms of a map of the minimum flux of a point source which would be expected to be detected about half of the time. (Since this flux is obviously infinite for all points at which the exposure is zero, it is in practice often more convenient to work with the reciprocal map). Unfortunately, in both the 1XMM and the 2XMM detection algorithms, source candidates are accepted as valid as a function of not one but two independent, but in practice interfering, parameters (eboxdetect's LIKE and emldetect's DETML). The present author has shrunk from the task of disentangling this procedure. Since neither esensmap nor esensitivity provides a sensitivity recipe which is formally correct in respect to these two detection algorithms, we have at this time no way within the sas to make such maps.
However, useful as a sensitivity map may be, it is not essential in the context of simulations. At present, exposure maps are used as a stop-gap reciprocal sensitivity map. This results in incorrect non-zero values of the INV_SENSY column of the list of simulated sources. However, only the zero values are important for the simulation machinery, so it functions correctly nevertheless.
