Chandra and NuSTAR Follow-up Observations of Swift-BAT-selected AGNs

Abstract

Based on current models of the cosmic X-ray background (CXB), heavily obscured active galactic nuclei (AGNs) are expected to make up ∼10% of the peak emission of the CXB and ∼20% of the total population of AGNs, yet few of these sources have been recorded and characterized in current surveys. Here we present the Chandra follow-up observation of 14 AGNs detected by Swift -BAT. For five sources in the sample, NuSTAR observations in the 3–80 keV band are also available. The X-ray spectral fitting over the 0.3–150 keV energy range allows us to determine the main X-ray spectral parameters, such as the photon index and the intrinsic absorption, of these objects and to make hypotheses on the physical structures responsible for the observed spectra. We find that 13 of the 14 objects are absorbed AGNs, and one is a candidate Compton-thick AGN, having intrinsic absorption cm −2 . Finally, we verified that the use of NuSTAR observations is strategic to strongly constrain the properties of obscured AGNs, since the best-fit values we obtained for parameters such as the power-law photon index Γ and the intrinsic absorption changed sometimes significantly fitting the spectra with and without the use of NuSTAR data.