X-ray Coronal Properties of Swift/BAT-Selected Seyfert 1 Active Galactic Nuclei

TL;DR

This study constrains the coronal temperature of a large sample of Seyfert 1 AGN using high-quality X-ray data, revealing a mean temperature of 84 keV and no significant correlation with accretion parameters.

Contribution

First large-scale analysis of Seyfert 1 AGN coronal temperatures using NuSTAR and Swift/XRT/XMM-Newton data with physically-motivated spectral modeling.

Findings

Mean coronal temperature is 84 keV.

No significant correlation between cutoff energy and Eddington ratio.

No significant correlation between photon index and Eddington ratio.

Abstract

The corona is an integral component of Active Galactic Nuclei (AGN) which produces the bulk of the X-ray emission above 1--2 keV. However, many of its physical properties and the mechanisms powering this emission remain a mystery. In particular, the temperature of the coronal plasma has been difficult to constrain for large samples of AGN, as constraints require high quality broadband X-ray spectral coverage extending above 10 keV in order to measure the high energy cutoff, which provides constraints on the combination of coronal optical depth and temperature. We present constraints on the coronal temperature for a large sample of Seyfert 1 AGN selected from the Swift/BAT survey using high quality hard X-ray data from the NuSTAR observatory combined with simultaneous soft X-ray data from Swift/XRT or XMM-Newton. When applying a physically-motivated, non-relativistic disk reflection model to the X-ray spectra, we find a mean coronal temperature kT $=$ 84$\pm$9 keV. We find no significant correlation between the coronal cutoff energy and accretion parameters such as the Eddington ratio and black hole mass. We also do not find a statistically significant correlation between the X-ray photon index, $\Gamma$, and Eddington ratio. This calls into question the use of such relations to infer properties of supermassive black hole systems.