SIMBAD references

The Galactic superluminal source GRS 1915+105 was found to experience a peculiar X-ray variability in a narrow count rate range (9300-12,100 counts.s^–1, 5 PCUs) of the Proportional Counter Array on board the Rossi X-Ray Timing Explorer. This can be seen as a ring-shaped pattern in the two-color diagram of count rates, where the hard hardness F(13-40 keV)/F(2-13 keV) is plotted against the soft hardness F(5-13 keV)/F(2-5 keV). The system runs one cycle with periods ranging between 50 and 100 s for different observations, one rotation in the two-color diagram corresponding to the time between two contiguous maxima in the light curve. We model this behavior successfully with the help of a self-consistent two-phase thermal model in which seed photons from an optically thick classical disk are Comptonized in a hot spherical corona surrounding the inner disk (Poutanen & Svensson; Vilhu et al.; Nevalainen et al.). In the model, changes of two parameters regulate the paths in the two-color diagram: the blackbody temperature T_in of the inner disk and the Thomson optical depth multiplied by the electron temperature of the hot phase τT_e. These parameters oscillate with time but with a phase shift between each other, causing the ring-shaped pattern. During the observation studied in more detail (20402-01-30-00), the inner disk radius varied with a 97 s period between 20 and 35 km with an anticorrelation between the coronal τT_e and the mass accretion rate M{dot} through the disk, possibly indicating a coupling between the disk and coronal accretion. During a typical cycle, the inner disk radius rapidly shrank and returned more slowly back to the original larger value. In the rings we may see phenomena close to the black hole horizon under near Eddington accretion rates.