2006ApJ...643.1114M

Using nonlinear time series analysis, along with surrogate data analysis, it is shown that the various types of long-term variability exhibited by the black hole system GRS 1915+105 can be explained in terms of a deterministic nonlinear system with some inherent stochastic noise. Evidence is provided for a nonlinear limit cycle origin of one of the low-frequency QPOs detected in the source, while some other types of variability could be due to an underlying low-dimensional chaotic system. These results imply that the partial differential equations that govern the magnetohydrodynamic flow of the inner accretion disk can be approximated by a small number (~3-5) of nonlinear but ordinary differential equations. While this analysis does not reveal the exact nature of these approximate equations, they may be obtained in the future, after results of magnetohydrodynamic simulation of realistic accretion disks become available.