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The limited angular resolution of gamma-ray telescopes prevents a directidentification of the majority of sources detected so far. This is particularlytrue for the low latitude, probably galactic, ones only 10 % of which has beenidentified. Most counterparts of the identified low-latitude gamma-ray sourcesare Isolated Neutron Stars (INS), both radio-loud and radio-quiet(Geminga-like) objects, which are characterised by an extremely high value ofthe X-ray-to-optical flux ratio f_X/f_opt. Therefore, the systematic X-ray andoptical coverage of low-latitude unidentified gamma-ray sources aiming at highf_X/f_opt sources seems one of the most promising ways to spot INS candidatecounterparts. Since low latitude sources are heavily affected by theinterstellar absorption at both X-ray and optical wavelengths, we have focussedon two middle-latitude, probably galactic, GRO/EGRET sources: 3EG J0616-3310and 3EG J1249-8330. These two sources, which could belong to a local galacticpopulation, have been selected owing to their relatively good positionalaccuracy, spectral shape and lack of candidate extragalactic radiocounterparts. Here we report on X-ray observations of the two gamma-ray errorboxes performed with XMM-Newton and on their optical follow-up carried on withthe Wide Field Imager at the ESO/MPG 2.2m telescope. Less than half of the ~300sources detected by the X-ray coverage have no optical counterparts. Amongthose, we have selected few interesting sources with f_X/f_opt > 100, which weconsider promising INS candidates.Comment: 18 pages, 10 figures, 8 tables. Accepted for publication by Astronomy  & Astrophysic

XMM-Newton and ESO observations of the two unidentifiedγ-ray sources 3EG J0616-3310 and 3EG J1249-8330