Final verdict from XMM-Newton: The X-ray obscured Seyfert galaxy NGC 5506 has a broad Fe Kα line

We present the first unambiguous evidence of a broad (Gaussian width∼330 eV) component of the iron Kα 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 Kα 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.