Black Hole X-ray Binaries (BHXRBs) consist of a black hole and a companion star, with
X-ray emission resulting from accretion onto the black hole. Material from the companion
flows through Roche-lobe overflow or stellar wind, forming an accretion
disk. Low-frequency quasi-periodic oscillations (LFQPOs), are commonly observed in these
systems and are thought to originate from the innermost accretion disk.

Key questions in high-energy astrophysics, such as the origin of LFQPOs, the nature and
distribution of the corona, mechanisms powering the corona, and the role of black hole
spin in jet ejection and coronal emission, remain unresolved.

In this seminar, I will present the results of the temporal and spectral properties of
BHXRBs containing nearly maximally spinning black holes. Specifically, I will discuss
the temporal and spectro-temporal analysis of the BHXRB system GRS 1915+105 using data
from AstroSat, focusing on a wide range of Type-C QPOs and HFQPOs. I will explore the
dynamical frequency model and its correlation with observational results. Furthermore, I
will discuss the temporal properties of GRS 1915+105 using AstroSat and NICER data,
highlighting the observed variability and its energy-dependent evolution. Finally, I
will share findings on the state evolution of the BHXRB GX 339-4, transitioning from
hard to soft states, based on observations from NICER, NuSTAR, and HXMT.