Andrea Goldwurm (CEA - Saclay, France)

An alternative 2-D detector plane for the Wide Field Monitor of LOFT

The WFM is the secondary instrument of the LOFT mission whose main objective is to provide unambiguous
detection of the high-energy sources in a large field of view, in order to support science operations of the
primary instrument, the Large Area Detector (LAD). The WFM is based on the coded aperture concept where
a position sensitive detector records the shadow of a mask projected by the celestial sources.
We propose to equip the WFM with sensors based on Double Sided micro-Strip Silicon Detectors (DSSD),
that allow fine 2-dimensional recording of the projected shadows. By allowing the incoming photons to be
positioned in both directions with equivalent fine resolution, the proposed instrument will provide the best
imaging capability compatible with the allocated budgets for this telescope on LOFT. This is an alternative
design compared to the initial WFM design baseline that is based on SDD sensors and which have fine
positional resolution only along one direction. The proposed 2D solution, which is now considered as a
possible option for the assessment studies of the mission, will reduce significantly the source confusion
experienced by the WFM in crowded regions of the sky and will in general increase the observatory science
capability of LOFT. We describe here this 2D DSSD option for the WFM, present a number of simulated
results and discuss the advantages that it may offer to the LOFT mission.