The nuclear X-ray emission in radio-quiet Active Galactic Nuclei (AGN) is commonly believed to be due to inverse Compton scattering of soft UV photons in a hot corona. The radiation is expected to be polarized, the polarization degree depending mainly on the geometry and optical depth of the corona. Nuclear Spectroscopic Telescope Array (NuSTAR) observations are providing for the first time high quality measurements of the coronal physical parameters-temperature and optical depth. We hereby review the NuSTAR results on the coronal physical parameters (temperature and optical depth) and discuss their implications for future X-ray polarimetric studies.
Marinucci, A., Tamborra, F., Bianchi, S., Dovčiak, M., Matt, G., Middei, R., et al. (2018). Hot coronae in local AGN: Present status and future perspectives. GALAXIES, 6(2), 44 [10.3390/galaxies6020044].