Hickox, RyanRyanHickoxCivano, FrancescaFrancescaCivanoBallantyne, D.D.BallantyneBalokovic, M.M.BalokovicBoorman, P.P.BoormanBrandt, W.W.BrandtCanning, R.R.CanningFornasini, F.F.FornasiniGandhi, P.P.GandhiJones, M.M.JonesLansbury, G.G.LansburyLanz, L.L.LanzLANZUISI, GiorgioGiorgioLANZUISIMadsen, K.K.MadsenMARCHESI, STEFANOSTEFANOMARCHESIMasini, A.A.MasiniAnanna, T.T.AnannaStern, D.D.SternRicci, C.C.Ricci2021-01-042021-01-0420192330-9458http://hdl.handle.net/20.500.12386/29463We review progress in understanding the high-energy X-ray emission from active galactic nuclei, and highlight exciting opportunities for a future high-resolution, hard (1-200 keV) X-ray observatory to resolve the cosmic X-ray background and characterize accreting supermassive black holes across cosmic time.ELETTRONICOenArticlehttps://baas.aas.org/pub/2020n3i468/release/12019BAAS...51c.468HFIS/05 - ASTRONOMIA E ASTROFISICA