Geometry of the AGN X-ray Corona

Determine the three-dimensional geometry of the X-ray emitting corona in active galactic nuclei by characterizing the angular distribution of coronal irradiation onto the accretion disk, in order to resolve how the incidence angle and coronal structure affect disk continuum reverberation mapping signals.

Background

Continuum reverberation mapping interprets interband lags as the response of the UV–optical accretion disk to variable X-ray irradiation from a compact corona. The geometry of this corona (e.g., its spatial extent and the angles at which it illuminates the disk) directly influences the timing and spectral signatures of reprocessing.

The simulations in this paper employ local shearing-box models that cannot capture global geometric effects such as the incidence angle distribution of coronal photons across the disk surface. The authors argue that global simulations are needed to study these effects and explicitly identify the corona’s geometry as an open question that must be probed to advance reverberation modeling.

References

With global simulations we can also examine the impact of the angle at which the disk is irradiated, allowing us to probe the open question of corona geometry.

— Continuum Reverberation in Active Galactic Nuclei Disks Only With Sufficient X-ray Luminosity and Low Albedo  (2501.06304 - Secunda et al., 10 Jan 2025) in Discussion (Section 5)

Despite decades of observational and theoretical efforts, the physical properties of these coronal components (such as their temperature, optical depth, and geometry) remain key open questions in AGN astrophysics.

— AGN X-ray coronae at high luminosity: A broadband study of RBS 229 and PG 1407+265  (2609.01265 - Lai et al., 1 Sep 2026) in Section 1, Introduction