INTEGRAL view of AGN

TL;DR

This review highlights INTEGRAL's significant contributions to understanding active galactic nuclei (AGN) through high-energy observations, including spectral characterization, population studies, and testing unification models, with future prospects across multiple wavelengths.

Contribution

It provides a comprehensive overview of INTEGRAL's impact on AGN research, emphasizing new discoveries and the integration of multi-wavelength data.

Findings

Catalogued around 450 AGN, including many observed at high energies for the first time.

Characterized AGN spectra in the 20-200 keV range, revealing absorption properties.

Supported the AGN unification scheme and advanced population studies.

Abstract

AGN are among the most energetic phenomena in the Universe and in the last two decades INTEGRAL's contribution in their study has had a significant impact. Thanks to the INTEGRAL extragalactic sky surveys, all classes of soft X-ray detected (in the 2-10 keV band) AGN have been observed at higher energies as well. Up to now, around 450 AGN have been catalogued and a conspicuous part of them are either objects observed at high-energies for the first time or newly discovered AGN. The high-energy domain (20-200 keV) represents an important window for spectral studies of AGN and it is also the most appropriate for AGN population studies, since it is almost unbiased against obscuration and therefore free of the limitations which affect surveys at other frequencies. Over the years, INTEGRAL data have allowed to characterise AGN spectra at high energies, to investigate their absorption properties, to test the AGN unification scheme and to perform population studies. In this review the main results are reported and INTEGRAL's contribution to AGN science is highlighted for each class of AGN. Finally, new perspectives are provided, connecting INTEGRAL's science with that at other wavelengths and in particular to the GeV/TeV regime which is still poorly explored.