2010MNRAS.406.2013G

We present the first unambiguous evidence of a broad (Gaussian width ∼330 eV) component of the iron K_α fluorescent emission line in the X-ray obscured narrow-line Seyfert 1 galaxy, NGC 5506. This is the main result of a spectroscopic monitoring campaign on this source, performed with the XMM-Newton observatory between 2001 February and 2009 January. The broad line lacks extreme redward skewness. If modelled with a relativistic component, the profile of the line is consistent with a flat emissivity radial dependence (α ≃ 1.9). The disc inclination (≃40°) is nominally larger than typically observed in unobscured active galactic nuclei (AGNs), in agreement with most measurements of broadened iron lines in Seyfert 2 galaxies. The quality of the data allows us to decompose the full iron emission-line complex, and to study its long-term (time-scales of weeks to yr) variability pattern. The intensity of the neutral and narrow iron K_α core remains constant during the monitoring campaign. This indicates that the optically thick gas responsible for the non-relativistic reprocessing of the primary AGN continuum in NGC 5506 is probably located in the torus rather than in the optical broad-line region.