Blueshifted lines from the inner accretion disc's rotation can explain quasar absorption "forests''

TL;DR

The paper proposes that blueshifted absorption lines in quasars originate from thin rings of material above the accretion disc, allowing us to probe the inner disc structure directly.

Contribution

It introduces a model where relativistic blueshifts are caused by disc motion, not outflows, explaining observed absorption forests in XRISM data.

Findings

Model reproduces observed absorption line shifts and separations.

Absorption rings are located between ISCO and 15r_g.

The model links absorption features to the inner disc surface structure.

Abstract

Recent XRISM observations of active galactic nuclei such as PDS 456 have revealed ``forests'' of absorption lines best modeled by five distinct absorption zones with varying large blueshifts. We propose a model in which these relativistic blueshifts originate from the motion of the accretion disc itself, rather than from a clumpy super-Eddington outflow at hundreds of gravitational radii $r_g\equiv GM/c^2$. We demonstrate that thin rings of absorbing material lying just above the accretion disc at varying radii can produce the observed energy shifts and separations of the absorption zones. In this model, the PDS 456 transmission spectrum is well reproduced by rings with widths $\Delta r\lesssim1r_g$ at locations between the black hole's innermost stable circular orbit (ISCO) and $\approx15r_g$. This model suggests that the absorption forests seen in XRISM observations can probe the surface structure of the innermost ($\lesssim15r_g$) regions of quasar accretion discs.