Constraints on the spacetime metric around seven "bare" AGNs using X-ray reflection spectroscopy

Abstract

We present the study of a sample of seven "bare" active galactic nuclei (AGN) observed with Suzaku. We interpret the spectrum of these sources with a relativistic reflection component and we employ our model RELXILL_NK to test the Kerr nature of their supermassive black holes. We constrain the Johannsen deformation parameters $\alpha_{13}$ and $\alpha_{22}$, in which the Kerr metric is recovered when $\alpha_{13} = \alpha_{22} = 0$. All our measurements are consistent with the hypothesis that the spacetime geometry around these supermassive objects is described by the Kerr solution. For some sources, we obtain quite strong constraints on $\alpha_{13}$ and $\alpha_{22}$ when compared to those found in our previous studies. We discuss the systematic uncertainties in our tests and the implications of our results.