Multi-epoch analysis of the X-ray spectrum of the active galactic nucleus in NGC 5506

Abstract

We present a multi-epoch X-ray spectroscopy analysis of the nearby narrow-line Seyfert I galaxy NGC 5506. For the first time, spectra taken by Chandra, XMM–Newton, Suzaku, and NuSTAR– covering the 2000–2014 time span – are analysed simultaneously, using state-of-the-art models to describe reprocessing of the primary continuum by optical thick matter in the active galactic nucleus environment. The main goal of our study is determining the spin of the supermassive black hole (SMBH). The nuclear X-ray spectrum is photoelectrically absorbed by matter with column density ≃ 3 × 1022 cm−2. A soft excess is present at energies lower than the photoelectric cut-off. Both photoionized and collisionally ionized components are required to fit it. This component is constant over the time-scales probed by our data. The spectrum at energies higher than 2 keV is variable. We propose that its evolution could be driven by flux-dependent changes in the geometry of the innermost regions of the accretion disc. The black hole spin in NGC 5506 is constrained to be 0.93 ±^(0.04)_(0.04) at 90 per cent confidence level for one interesting parameter.