Swift XRT Observation of 34 New INTEGRAL IBIS AGNs: Discovery of Compton-Thick and Other Peculiar Sources
For a significant number of the sources detected at high energies (>10 keV) by the INTEGRAL IBIS and Swift BAT instruments there is either a lack information about them in the 2-10 keV range or they are totally unidentified. Herein, we report on a sample of 34 IBIS AGNs or AGN candidate objects for which there is X-ray data in the Swift XRT archive. Thanks to these X-ray follow-up observations, the identification of the gamma-ray emitters has been possible and the spectral shape in terms of photon index and absorption has been evaluated for the first time for the majority of our sample sources. The sample, enlarged to include four more AGNs already discussed in the literature, has been used to provide photon index and column density distribution. We obtain a mean value of 1.88 with a dispersion of 0.12, i.e., typical of an AGN sample. Sixteen objects (47%) have column densities in excess of 1022 cm-2 and, as expected, a large fraction of the absorbed sources are within the Sey 2 sample. We have provided a new diagnostic tool (NH vs. F2-10keV/F20-100keV softness ratio) to isolate peculiar objects; we find at least one absorbed Sey 1 galaxy, three Compton-thick AGN candidates; and one secure example of a ``true'' type 2 AGN. Within the sample of 10 still unidentified objects, 3 are almost certainly AGNs of type 2; 3-4 have spectral slopes typical of AGN; and 2 are located high on the Galactic plane and are strong enough radio emitters that they can be considered good AGN candidates.