Study of Timing Evolution from Non-Variable to Structered Large-Amplitude Variability Transition in GRS 1915+105 Using AstroSat/LAXPC

In this work, we present a ∼90 ks continuous monitoring of the Galactic micro-quasar GRS 1915+105with AstroSat when the source undergoes a major transition from a non-variable, radio-quiet χ class (χRQ ) to a structured, large amplitude, periodic flaring state (similar to ρ class). We show that suchtransition takes place via an intermediate state when the large-amplitude, irregular variability of theorder of hundreds of seconds in the soft X-ray band turned into a 100-150 sec regular, structured,nearly periodic flares similar to ρ class/heartbeat oscillations. The properties of a strong low-frequencyquasi-periodic oscillations (LF QPO) in the frequency range 3-5 Hz also evolve marginallyduring these variability transitions. We also study time-lag spectra at the QPO and harmonic componentand the dynamic power spectra. The relative stability of LF QPOs implies the inner disk-coronacoupled accretion flow which determines the LF QPO properties, may be uninterrupted by the launchof long, large-amplitude flares.