Optical spectroscopic survey of a sample of Unidentified Fermi objects: II

Abstract: We report on optical spectroscopy obtained at the 10.4m Gran Telescopio Canarias of 28 Fermi gamma-ray sources that completes the study of a sample of 60 targets of unidentified objects for which the detection of an X-ray and/or radio source inside the 3FGL error box is available. The observations are aimed to characterize the nature and measure the redshift of these sources. For all optical counterparts, the observations allow us to establish their AGN nature. In particular, we found 24 BL Lac objects, one QSO, one NLSy1 and two objects showing spectral features typical of Seyfert 2 galaxies. For most of them, we determine a spectroscopic redshift, while for five we can set lower limits based on the lack of stellar features from the host galaxy. The global properties of the full sample are briefly discussed.