Median High-energy Cutoff in the Hard X-ray Spectra of Swift/BAT-selected Type II AGN

Broadband X-ray spectroscopy of the X-ray emission produced in the coronae of active galactic nuclei (AGN) can provide important insights into the physical conditions very close to their central supermassive black holes (SMBHs). The temperature of the Comptonizing plasma that forms the corona is manifested through a high-energy cutoff that has been difficult to directly constrain even in the brightest AGN because it requires high-quality data at energies above 10 keV. We present the first large collection of coronal cutoff constraints for obscured AGN based on a sample of 130 AGN selected from the Swift/BAT all-sky survey and observed nearly simultaneously with NuSTAR and Swift/XRT. Under a reasonable set of assumptions the median high-energy cutoff is well constrained to 290 keV with a statistical uncertainty of only 20 keV (68% confidence level). Taking into account various systematic uncertainties, we place the median cutoff energy robustly in the energy range between 240 and 340 keV. This result implies that phenomenological parameters of the coronal continuum in obscured AGN and unobscured AGN are not substantially different given the known uncertainties. The high-energy cutoff does not appear to show any clear trends with respect to either line-of-sight obscuration, intrinsic luminosity, or Compton hump strength.