Quasi-periodic oscillations and spectral states in GRS 1915+105

We present results from the analysis of X-ray energy spectra and quasi-peri odic oscillations (QPOs) from a set of observations that samples a broad ra nge of time variability in GRS 1915+105. We first demonstrate that the freq uency and integrated amplitude of a 0.5-10 Hz QPO is correlated with the ap parent temperature of the accretion disk for the majority of observations. We then show that the behavior of GRS 1915+105 exhibits two distinct modes of accretion. In the first mode, the QPO is present between 0.5 and 10 Hz a nd variability in the source luminosity is dominated by the power-law compo nent. In the second mode, the QPO is absent and the changes in the luminosi ty are dominated by thermal emission from the accretion disk. We find that the color radius and temperature of the inner accretion disk are empiricall y related by R-col proportional to T-col(-2) + const. We discuss these resu lts in terms of ongoing efforts to explain the origin of both the QPOs and the hard X-ray component in the spectrum of GRS 1915 + 105.