How the effects of resonant absorption on black hole reflection spectra can mimic high-velocity outflows

TL;DR

This paper proposes that narrow absorption lines in black hole spectra, traditionally attributed to high-velocity outflows, could instead result from resonant absorption by ionized iron in the accretion disc's hot plasma, offering an alternative explanation.

Contribution

It introduces a reflection-based model where resonant absorption by ionized iron in the disc's hot plasma can mimic high-velocity outflow signatures in spectra.

Findings

Resonant absorption can produce narrow features between 4-10 keV.

No need for high-velocity outflows to explain observed features.

The model is consistent with reflection-based interpretations.

Abstract

Narrow absorption lines seen in the 2-10 keV spectra of active galaxies and Galactic black holes are normally attributed to iron in high velocity outflows or inflows. We consider the possibility that such features could arise naturally in the accretion disc. Resonant absorption by highly ionised iron (e.g. Fe XXVI and Fe XXV) in an optically-thin plasma that is located above the disc and rotating with it could reproduce narrow features in the reflection component of the spectrum as it emerges from the disc. Depending on the inclination of the disc and the exact geometry of the hot plasma (e.g. does it blanket the disc or a ring) apparently narrow absorption features could be detected between 4-10 keV. Such an explanation requires no high velocity outflow/inflow and is consistent with a reflection-based interpretation for accreting black holes systems.