High-soft to low-hard state transition in black hole X-ray binaries with GRMHD simulations

To understand the decaying phase of outbursts in the black hole (BH) X-ray binaries (BH-XRBs), we performed very long general relativistic magneto-hydrodynamic (GRMHD) simulations of a geometrically thin accretion disk around a Kerr BH with slowly rotating matter injected from outside. We thoroughly studied the flow properties, dynamical behavior of the accretion rate, magnetic flux rate, and jet properties during the temporal evolution. Due to the interaction between the thin disk and injected matter, the accretion flow near the BH goes through different phases. The sequence of phases is: soft state $\rightarrow$ soft-intermediate state $\rightarrow$ hard-intermediate state $\rightarrow$ hard state $\rightarrow$ quiescent state. For the accretion rate (and hence the luminosity) to decrease (as observed) in our model, the mass injection should not decay slower than angular momentum injection. We also observed quasi-periodic oscillations (QPOs) in the accretion flow. Throughout the evolution, we observed low-frequency QPOs (~10Hz) and high-frequency QPOs (\sim 200Hz). Our simple unified accretion flow model for state transitions is able to describe outbursts in BH-XRBs.