Probing the geometry and motion of AGN coronae through accretion disc emissivity profiles

TL;DR

This paper investigates how different geometries of AGN coronae affect the X-ray illumination patterns on accretion disks, using simulations to identify observable differences in emissivity profiles and spectra.

Contribution

It introduces a comprehensive simulation approach to distinguish corona geometries via emissivity profiles, reflection fractions, and spectral features in AGN studies.

Findings

Emissivity profiles differ significantly between point and extended geometries.

Reflection fraction analysis helps differentiate point sources from conical geometries.

Spectral differences among geometries are up to 15% in extreme cases.

Abstract

To gain a better understanding of the inner disc region that comprises active galactic nuclei it is necessary to understand the pattern in which the disc is illuminated (the emissivity profile) by X-rays emitted from the continuum source above the black hole (corona). The differences in the emissivity profiles produced by various corona geometries are explored via general relativistic ray tracing simulations. Through the analysis of various parameters of the geometries simulated it is found that emissivity profiles produced by point source and extended geometries such as cylindrical slabs and spheroidal coronae placed on the accretion disc are distinguishable. Profiles produced by point source and conical geometries are not significantly different, requiring an analysis of reflection fraction to differentiate the two geometries. Beamed point and beamed conical sources are also simulated in an effort to model jet-like coronae, though the differences here are most evident in the reflection fraction. For a point source we determine an approximation for the measured reflection fraction with the source height and velocity. Simulating spectra from the emissivity profiles produced by the various geometries produce distinguishable differences. Overall spectral differences between the geometries do not exceed 15 per cent in the most extreme cases. It is found that emissivity profiles can be useful in distinguishing point source and extended geometries given high quality spectral data of extreme, bright sources over long exposure times. In combination with reflection fraction, timing, and spectral analysis we may use emissivity profiles to discern the geometry of the X-ray source.