Non-Linear Dynamics of Accretion Disks with Stochastic Viscosity

TL;DR

This paper introduces a non-linear numerical model for accretion disks incorporating stochastic viscosity fluctuations, successfully reproducing observed phenomena like the rms-flux relationship and coherence patterns seen in astrophysical sources.

Contribution

The study presents a novel non-linear stochastic model for accretion disks that captures key observational features not explained by previous linear models.

Findings

Reproduces the linear rms-flux relationship in disk luminosity.

Shows coherence in dissipation and accretion rates below viscous frequency.

Aligns with observed coherence in sources like Cygnus X-1.

Abstract

We present a non-linear numerical model for a geometrically thin accretion disk with the addition of stochastic non-linear fluctuations in the viscous parameter. These numerical realizations attempt to study the stochastic effects on the disk angular momentum transport. We show that this simple model is capable of reproducing several observed phenomenologies of accretion driven systems. The most notable of these is the observed linear rms-flux relationship in the disk luminosity. This feature is not formally captured by the linearized disk equations used in previous work. A Fourier analysis of the dissipation and mass accretion rates across disk radii show coherence for frequencies below the local viscous frequency. This is consistent with the coherence behavior observed in astrophysical sources such as Cygnus X-1.