Stochastic dynamical description of κ and ρ bursting classes of the microquasar GRS 1915+105

Abstract

ABSTRACT We applied a stochastic analysis based on the Langevin equation to some bursting X-ray light curves of the bright microquasar GRS 1915+105. These time series, obtained with the PCA instrument onboard Rossi-XTE, are typical of the ρ and κ classes, which are characterized by several recurring bursts with different profiles and recurrence times. We computed the state functions which are able to capture the main dynamical properties of these light curves. In the case of the κ class, the state functions in four energy bands have a double-well structure (two stable states with an unstable one in between) and the system oscillates from one to the other minimum describing a typical hysteresis cycle, as in the case of a stochastic resonance under a forcing input. For the ρ class, the functions have only one stable state followed by an unstable interval, and the system describes a limit cycle. We also performed a new spectral analysis of these data with a multitemperature zero torque accretion disc model and used the resulting parameters for interpreting the main properties of the stochastic description.