Understanding the dynamics behind black hole state transitions and the
changes they reflect in outbursts has become long-standing problem. The X-ray
reflection spectrum describes the interaction between the hard X-ray source
(the power-law continuum) and the cool accretion disc it illuminates, and thus
permits an indirect view of how the two evolve. We present a systematic
analysis of the reflection spectrum throughout three outbursts (500+
observations) of the black hole binary GX 339-4, representing the largest study
applying a self-consistent treatment of reflection to date. Particular
attention is payed to the coincident evolution of the power-law and reflection,
which can be used to determine the accretion geometry. The hard state is found
to be distinctly reflection weak, however the ratio of reflection to power-law
gradually increases as the source luminosity rises. In contrast the reflection
is found dominate the power-law throughout most of the soft state, with
increasing supremacy as the source decays. We discuss potential dynamics
driving this, favouring inner disc truncation and decreasing coronal height for
the hard and soft states respectively. Evolution of the ionisation parameter,
power-law slope and high-energy cut-off also agree with this interpretation.Comment: Accepted for publication in MNRA
