Determining the nature of the unassociated Fermi-LAT gamma-ray sources

Fermi opened new horizons in gammaray astronomy, with 1873 sources detected bythe LAT instrument in the first 2 years. However, <10% of them are identified,mostly as gammaray pulsars or Active Galactic Nuclei (AGN), while virgul60% are onlyassociated with potential gammaray emitters matched in object catalogues. Theremaining virgul30% have not even a potential association. The nature of thesesources is unknown and can only be investigated through multiwavelengthobservations. Here, we propose to map the error boxes of selected LAT sourceswith XMM and the VLT. From the classification of their candidate Xraycounterparts, based on their Xray and optical properties, we will then singleout those which are most likely gammaray emitters and close the identification loop. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]