Discovery of a New Flaring Class in GRS 1915+105 Using AstroSat

Abstract The highly variable black hole X-ray binary GRS 1915+105 has shown many flaring classes when the source oscillates between the high soft state (HS) and the hard intermediate state with a transition time of less than 10 s. The X-ray flux is anticorrelated with the hardness ratio (HR2) during these X-ray flaring classes. We have analyzed Astrosat/Large Area X-ray Proportional Counter and Soft X-ray Telescope data and report here a new X-ray flaring class named η class when the source oscillates between two HS states (the power-law index is always greater than 4) with transition time around 50 s. The X-ray flux is correlated with the hardness ratio. This class is quasi-regular, and we have detected high-frequency quasiperiodic oscillations around 70 Hz during this new flaring class. The accretion rate changes by a factor of 3 over the burst cycle. We report here the results of our extensive study of spectral and timing characteristics of this new class.