State transition between high-soft and low-soft states observed in GRS 1915+105

Abstract

We present the results of a detailed analysis of RXTE observations which show an unusual state transition between high-soft and low-soft states in the microquasar GRS 1915+105. The RXTE pointed observations reveal that these events appeared as a series of quasi-regular dips when hard X-ray and radio flux were very low. The X-ray light curve and colour-colour diagram of the source during these observations are found to be different from any reported so far. The X-ray spectral and timing properties of the source during these dips are distinctly different from those seen during the other various dips and low intensity states seen in this source. There is, however, a remarkable similarity in the properties during the dip and non-dip regions in these set of observations. This indicates that the basic accretion disk structure is similar, but differ only in intensity. We invoke a model, to explain these observations, in which the viscosity is very close to a critical viscosity and the shock wave is weak or absent.