| Abstract : | Many accreting black holes and neutron stars exhibit rapid variability in their X-ray light curves termed quasi-periodic oscillations (QPOs); the most common type is the low-frequency (< 10 Hz) type-C QPOs. These QPOs are typically observed during the "hard" spectral state; a state in which the accretion flow is considered to be more complicated with two components: a geometrically, thick, hot corona surrounded by a geometrically thin, cold disc. Type-C QPOS are often associated with the Lense-Thirring precession of the inner, hot corona inclined by a certain angle with the black hole spin axis. However, none of the earlier works involves more realistic geometries that account for the surrounding geometrically thin disc. A matter of concern for these precession-based QPO models is the coupling between the outer, thin disc and the inner corona and how it affects the precession. In this talk, I will focus on our recent findings that address precisely this issue using state-of-the-art GRMHD simulations of a misaligned, truncated disc. Our results suggest that the inner, hot flow undergoes precession at a rate much less than the predicted rates for an isolated, precessing corona due to the presence of the outer, thin disc. The misalignment also excites variability in the inner, hot flow, which is otherwise absent in the aligned discs. |
