Evolution of Accreting Black Holes in X-ray Binaries

Accretion disks around compact objects like black holes and neutron stars provide an ideal environment to study the accretion phenomena in strong gravitational potentials. Accreting black holes in X-ray binaries (XRBs) and a sample of ultraluminous X-ray sources (ULXs) are known to undergo dramatic changes in their observed properties, which pose a great challenge to our understanding of the accretion phenomena around these objects. I will provide a brief introduction to these systems and first present the results from a systematic analysis of ~1800 RXTE observations of GRO J1655-40 and LMC X-3 to explore the nature of the accretion disk via non-relativistic and relativistic disk models. Our results show that non-relativistic modeling of these disks lead to a significant oversight of certain properties of the system as it evolves through different accretion states which can only be described by relativistic disk solutions. I will then report on the discovery of a new candidate ULX in M51 which contributes to a growing population of serendipitously discovered transient ULXs. I will then discuss its observed properties in the context of “transient accretion” and discuss the gap these sources give rise to in our understanding of accretion phenomena across the luminosity and black hole mass scale.