Probing the AGN Coronae with High-redshift AGN: PACHA

The X-ray emission of active galactic nuclei (AGN) is thought to originate from compact regions surrounding their central supermassive black holes (SMBHs), known as coronae. While coronae have been studied for decades, their physical and geometrical properties remain poorly understood. A major challenge is that the high-energy cutoff—the most prominent coronal feature in the X-ray spectrum, typically at a few hundred keV, lies beyond the sensitivity of current hard X-ray telescopes. Consequently, even with NuSTAR, cutoff energies are not well constrained for most AGN in the local Universe. High-redshift, luminous AGN, however, offer a unique opportunity to probe coronal properties thanks to cosmological redshifting, which brings the cutoff energy into the observable band. In this talk, I will present our recent effort, the Probing the AGN Coronae with High-redshift AGN (PACHA) project, which investigates a sample of eight high-z, radio-quiet AGN through 1.1 Ms of NuSTAR and 300 ks of XMM-Newton observations.