Exploring the high-density reflection model for the soft excess in RBS 1124

ABSTRACT ‘Bare’ active galactic nuclei (AGN) are a subclass of Type 1 AGN that show little or no intrinsic absorption. They offer an unobscured view of the central regions of the AGN and therefore serve as ideal targets to study the relativistic reflection features originating from the innermost regions of the accretion disc. We present a detailed broad-band spectral analysis (0.3–70 keV) of one of the most luminous bare AGN in the local Universe, RBS 1124 ($z= 0.208$) using a new, co-ordinated high signal-to-noise observation obtained by XMM–Newton and NuSTAR. The source exhibits a power-law continuum with $\Gamma \sim$ 1.8 along with a soft excess below 2 keV, a weak neutral iron line and curvature at high energies (${\sim} 30$ keV). The broad-band spectrum, including the soft excess and the high-energy continuum, is well fit by the relativistic reflection model when the accretion disc is allowed to have densities of log$(n_{\rm e}$/cm$^{-3}$) $\gtrsim 19.2$. Our analysis therefore suggests that when high-density effects are considered, relativistic reflection remains a viable explanation for the soft excess.