The populations of hard X-ray and γ-ray sources: a correlation study and new possible identifications

Aims: We present the results of our analysis devoted to researching Galactic and extragalactic sources emitting in the energy bands surveyed by both the Swift-BAT and the Fermi-LAT telescopes.
Methods: We cross-correlated the Fermi-LAT 1-year point source catalogue (1FGL) of gamma-ray sources and the second Palermo BAT catalogue (2PBC) of hard X-ray sources, establishing a correspondence between sources when their error boxes overlap. With dedicated software for reducing BAT data, we also extracted the value of the detection significance σ in the BAT 15-150 keV all-sky map in the direction of the 1FGL sources and took those above the threshold σ_T^{star = 3} into account.
Results: We obtain 62 firm correspondences by cross-correlating the 1FGL and 2PBC catalogues and verifying the agreement between the identified counterparts. The number of objects emitting in both the hard X-ray and the γ-ray energy bands rises to 104 ( 7% of all the 1FGL objects) when considering all the sources with a detection significance down to σ_T^star. This group of objects is made of 82 extragalactic sources, the largest number of which are blazars, 15 Galactic sources, and seven unidentified objects. We discuss the blazar content of the collected 1FGL-2PBC sources and compare their redshift distribution with that of the whole blazar population as reported in the second edition of the BZCAT blazar catalogue. We describe in greater detail the properties of two unidentified sources at low Galactic latitude, 1FGL J0137.8+5814 and 1FGL J2056.7+4938, and support their classification as blazars after the analysis of their broad-band spectral energy distribution.