X-Ray Fluctuations from Advection-dominated Accretion Disks with a Critical Behavior

摘要

A new hydrodynamic model for aperiodic X-ray fluctuations from black hole objects is presented. X-ray fluctuation is thought to originate from instabilities of the accretion disk around a black hole. We previously proposed the cellular automaton model based on the notion of self-organized criticality to describe the open, dissipative nature of a disk undergoing instabilities. Assuming that an avalanche was triggered when the mass density exceeded some critical value, we could reproduce the basic statistical features of X-ray variability with this model. As an independent inquiry, we also calculated the response of an axisymmetric, advection-dominated disk to thermal perturbations, demonstrating that it can easily produce an X-ray shot as is observed in X-ray fluctuations.