The NuSTAR Serendipitous Survey: Hunting for the Most Extreme Obscured AGN at >10 keV
G. B. Lansbury et al 2017 ApJ 846 20
Eight NuSTAR sources with extremely hard X-ray spectra are identified as highly obscured active galactic nuclei, including three robust Compton-thick AGN at low redshift and one likely one at higher redshift.