A model-independent analysis of the variability of GRS 1915+105

We analyzed 163 observations of the microquasar GRS 1915+105 made with the Rossi X-ray Timing Explorer (RXTE) in the period 1996-1997. For each observ ation, we produced light curves and color-color diagrams. We classified the observations in 12 separate classes, based on their count rate and color c haracteristics. From the analysis of these classes, we reduced the variabil ity of the source to transitions between three basic states: a hard state c orresponding to the non-observability of the innermost parts of the accreti on disk, and two softer states with a fully observable disk. These two soft states represent different temperatures of the accretion disk, related to different local values of the accretion fate. The transitions between these states can be extremely fast. The source moves between these three states following certain patterns and avoiding others, giving rise to a relatively large but limited number of variability classes. These results are the fir st step towards a linking of the properties of this exceptional source with standard black-hole systems and with accretion disk models.