The final verdict by XMM-Newton: the X-ray obscured Seyfert galaxy NGC5506 has a broad Fe K-alpha line

TL;DR

This study provides the first clear detection of a broad Fe K-alpha line in the X-ray spectrum of NGC5506, revealing details about the accretion disk and torus structure in this obscured Seyfert galaxy.

Contribution

It presents unambiguous evidence of a broad Fe K-alpha line in NGC5506 and analyzes its properties and variability over nearly a decade of observations.

Findings

Detection of a broad Fe K-alpha line with Gaussian width ~330 eV

Line profile consistent with a flat emissivity radial dependence (~1.9)

The narrow Fe K-alpha core remains constant over time

Abstract

We present the first unambiguous evidence of a broad (Gaussian width ~330 eV) component of the iron K-alpha fluorescent emission line in the X-ray obscured Narrow Line Seyfert 1 Galaxy NGC5506. This is the main results of a spectroscopic monitoring campaign on this source performed with the XMM-Newton observatory between February 2001 and January 2009. The broad line lacks extreme redwards skewness. If modelled with a relativistic component, the profile of the line is consistent with a flat emissivity radial dependence (alpha~1.9). The disk inclination (~40 degrees) is nominally larger then typically observed in unobscured AGN, 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 (timescales of weeks to years) variability pattern. The intensity of the neutral and narrow iron K-alpha 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 NGC5506 is probably located in the torus rather than in the optical Broad Line Region.