Decoding Imprints of Black Hole Accretion: Investigations through X-ray Timing and Spectro-Polarimetry

Abstract

Accretion is a fundamental astrophysical process that powers a large fraction of the energy output observed in the X-ray sky. In accretion powered binary systems, known as X-ray binaries (XRBs), a compact object accretes matter from a companion star, leading to X-ray emission. Among these, black hole systems are of particular interest due to their extreme gravitational fields, which make direct observation of their interiors impossible. As a result, black hole XRBs serve as natural laboratories for probing strong gravity through indirect observations. Their high accretion efficiency leads to substantial Xray output, detected by space-based observatories. From this, X-ray photons recorded in time and energy bins reveal the temporal and spectral properties of the emission, while the orientation of their electric fields carries polarimetric information. This thesis analyzes such observational data from various X-ray observatories (AstroSat, NICER, NuSTAR, IXPE, MAXI, Swift, XMM-Newton) to investigate the accretion dynamics of various galactic and extragalactic black hole sources.