Jacob Howard

UC Santa Barbara

Investigation of Corrugation Modes as a Mechanism for X-Ray Variability

The study of black hole accretion flows is strongly motivated by evidence that observed X-rays emitted from stellar objects such as active galactic nuclei (AGN) and black hole binaries (BHB) are generated by the accretion of material onto black holes. Despite the wide variety of size and mass among these systems, the intensity of these X-ray emissions consistently exhibit periodic oscillations that are driven by processes that are not well-understood. Systematic study of the dynamical elements in these accretion flows is therefore critical to uncovering the underlying mechanism responsible for this oscillatory behavior. In this project, we use the fully three-dimensional, general relativistic, magnetohydrodynamical simulation code Athena++ to study the spatial and temporal structure of untilted accretion flows around spinning black holes. We compare two simulations with identical initial conditions but two levels of resolution. Our analysis of the lower-resolution data reveals clear variability in the flow structure at multiple radii. However, our analysis of the higher-resolution data in which turbulence develops more realistically lacks the presence of these periodic features. The absence of these structures in high-resolution, fully general relativistic, magnetohydrodynamical simulations suggests that turbulence driven by magnetorotational instabilities may prevent coherent modes from propagating in untilted accretion disks.

UC Santa Barbara Center for Science and Engineering Partnerships UCSB California NanoSystems Institute