XMM-Newton observations of the Lockman Hole: III. A relativistic Fe line in the mean X-ray spectra of type-1 and type-2 AGN

TL;DR

This study analyzes the average X-ray spectra of AGN in the Lockman Hole, revealing a relativistic iron line profile indicative of spinning supermassive black holes, with implications for black hole spin and iron abundance.

Contribution

It provides the first evidence of relativistic Fe lines in both type-1 and type-2 AGN, suggesting significant black hole spin and super-solar iron abundance in the average AGN spectrum.

Findings

Relativistic Fe lines are present in both AGN types.

The inner disk radius suggests rapidly spinning black holes.

Iron abundance is about three times solar.

Abstract

Using the 770 ksec XMM-Newton survey of the Lockman Hole field in combination with extensive optical identifications of the AGN population, we derive an average rest-frame spectrum of AGN types-1 and 2. The most prominent feature in the averaged spectrum is a strong fluorescent Fe line. In both type-1 and type-2 AGN, a clear relativistic line profile is rev ealed. A laor line profile with an inner disk radius smaller than the last stabl e orbit of a Schwarzschild black hole is most consistent with the data, indicati ng that the average supermassive black hole has significant spin. Equivalent wid ths of the broad relativistic lines range between 400--600 eV. We used the disk reflection model to compare the observed strength of the line with the amplitude of the reflection component, concluding that to consistently describe the observations the average iron abundance should be about three times the solar value.