Kavli Affiliate: Daniel R. Wilkins
| Summary:
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 $r_gequiv GM/c^2$. 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 $Δrlesssim1r_g$ 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.
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