Chandra and NuSTAR follow-up observations of Swift-BAT selected AGN

TL;DR

This study uses Chandra and NuSTAR follow-up observations to analyze the X-ray spectra of Swift-BAT selected AGN, revealing that most are obscured and demonstrating the importance of NuSTAR data in constraining their properties.

Contribution

It provides detailed spectral analysis of obscured AGN using combined Chandra and NuSTAR data, highlighting the significance of NuSTAR in characterizing heavily obscured sources.

Findings

13 of 14 AGN are absorbed, with one candidate Compton thick.

NuSTAR data significantly improve spectral parameter constraints.

Most AGN in the sample are heavily obscured.

Abstract

Based on current models of the Cosmic X-ray Background (CXB), heavily obscured Active Galactic Nuclei (AGN) are expected to make up ~10% of the peak emission of the CXB and ~20% of the total population of AGN, yet few of these sources have been recorded and characterized in current surveys. Here we present the Chandra follow-up observation of 14 AGN 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 AGN, and one is a candidate Compton thick AGN, having intrinsic absorption NH>1E24 cm^{-2}. Finally, we verified that the use of NuSTAR observations is strategic to strongly constrain the properties of obscured AGN, since the best-fit values we obtained for parameters such as the power-law photon index and the intrinsic absorption NH changed sometimes significantly fitting the spectra with and without the use of NuSTAR data.