  The Large Observatory for X-ray Timing (LOFT) is one of the five candidates
that were considered by ESA as an M3 mission (with launch in 2022-2024). It is
specifically designed to exploit the diagnostics of very rapid X-ray flux and
spectral variability that directly probe the motion of matter down to distances
very close to black holes and neutron stars, as well as the physical state of
ultradense matter. The LOFT scientific payload is composed of the Large Area
Detector (LAD), devoted to spectral-timing observation, and the Wide Field
Monitor (WFM), whose primary goal it is to monitor the X-ray sky for transient
events that need to be followed up with the LAD, and to measure the long-term
variability of galactic X-ray sources and localize gamma-ray bursts. Here we
describe the simulations carried out to optimize the WFM design and to
characterize the instrument response to both isolated sources and crowded
fields in the proximity of the galactic bulge.
