A variability analysis of low-latitude unidentified gamma-ray sources

We present a study of 40 low-latitude unidentified 3EG gamma-ray sources wh ich were found to be not positionally coincident with any known class of po tential gamma-ray emitters in the Galaxy (Romero et al. 1999). We have perf ormed a variability analysis which reveals that many of these 40 sources ar e variable. These sources have in addition, a steep mean value of the gamma -ray spectral index, < Gamma > = 2.41 +/- 0.2, which, combined with the hig h level of variability. seems to rule out a pulsar origin. The positional c oincidences with uncatalogued candidates to supernova remnants were also st udied. Only 7 sources in the sample are spatially coincident with these can didates, a result that is shown to be consistent with the expected level of pure chance association. A complementary search for weak radio counterpart s was also conducted and the results are presented as an extensive table co ntaining all significant point-like radio sources within the 40 EGRET field s. Mie argue that in order to produce the high variability, steep gamma-ray spectra, and absence of strong radio counterparts observed in some of tile : gamma-ray sources of our sample. a new class of objects should be postula ted, and we analyze a visible candidate.