Astrophysics seeks to understand the mechanisms governing celestial objects and their interactions across the universe. Black hole X-ray binaries (BHXRBs) provide an exceptional laboratory for studying accretion physics, relativistic jets, and strong gravity effects. This thesis focuses on the evolution of BHXRBs in the X-ray band, analyzing their spectral and timing properties across different accretion states, including the hard state (HS), the soft-intermediate/soft state (SIMS/SS), and spin measurements via modeling the thermal emission of the disk (“continuum fitting”). A self-consistent analysis revealed that the disk-corona connection plays a crucial role in shaping the observed X-ray emission. Using data from multiple X-ray observatories, this work explores the evolution of the accretion disk and the corona geometry through advanced spectral odeling techniques. A key finding is that in the HS, contrary to the commonly held belief that the accretion disk is highly truncated, the inner disk is not necessarily truncated and could be non-truncated or slightly truncated, and the reflection fraction is close to unity as expected. This suggests a more complex corona-disk interaction than previously assumed. The transition to the soft-intermediate and soft states (SIMS/SS) is marked by the emergence of a self-obscured accretion disk, where a sudden decrease in the apparent inner disk temperature is accompanied by an increase in the inferred disk radius. This effect, derived from spectral modeling, is strongly dependent on the system’s inclination, suggesting that geometric obscuration plays a significant role in shaping the observed disk properties. Notably, this phenomenon appears to be a recurrent feature in major outbursts of highly inclined BHXRBs, indicating a common physical mechanism at play during the SIMS. Furthermore, this thesis presents a spin measurement of a BHXRB in the hard-intermediate state (HIMS) using the continuum-fitting method. The results indicate a low-spin black hole, effectively ruling out high spin when incorporating new dynamical constraints. The observed discrepancy between inclination estimates from continuum fitting and those obtained via relativistic reflection modeling suggests a potential misalignment between the inner accretion disk and the binary orbit, which may have significant implications for the angular momentum evolution of the system. These findings provide new insights into the accretion physics of BHXRBs, challenging traditional assumptions about disk truncation, corona geometry, and spin constraints. The results have broad implications for understanding accretion processes in strong gravity environments, with potential applications to other compact objects such as neutron stars and active galactic nuclei (AGN).
X-ray studies of accreting black hole X-ray binaries
Ubach Ramirez, S. (Author). 9 May 2025
Student thesis: Doctoral thesis
Student thesis: Doctoral thesis