Properties of AGN coronae in the NuSTAR era – II. Hybrid plasma

Abstract

The corona, a hot cloud of electrons close to the centre of the accretion\ndisc, produces the hard X-ray power-law continuum commonly seen in luminous\nActive Galactic Nuclei (AGN). The continuum has a high-energy turnover,\ntypically in the range of one to several 100 keV and is suggestive of\nComptonization by thermal electrons. We are studying hard X-ray spectra of AGN\nobtained with NuSTAR after correction for X-ray reflection and under the\nassumption that coronae are compact, being only a few gravitational radii in\nsize as indicated by reflection and reverberation modelling. Compact coronae\nraise the possibility that the temperature is limited and indeed controlled by\nelectron-positron pair production, as explored earlier (Paper I). Here we\nexamine hybrid plasmas in which a mixture of thermal and nonthermal particles\nis present. Pair production from the nonthermal component reduces the\ntemperature leading to a wider temperature range more consistent with\nobservations.\n