  Accreting black holes show a complex and diverse behaviour in their soft
spectral states. Although these spectra are dominated by a soft, thermal
component which almost certainly arises from an accretion disc, there is also a
hard X-ray tail indicating that some fraction of the accretion power is instead
dissipated in hot, optically thin coronal material. During such states, best
observed in the early outburst of Soft X-ray Transients, the ratio of power
dissipated in the hot corona to that in the disc can vary from ~0 (pure disc
accretion) to ~1 (equal power in each). Here we present results of spectral
analyses of a number of sources, demonstrating the presence of complex features
in their energy spectra. Our main findings are: (1) the soft components are not
properly described by a thermal emission from accretion discs: they are
appreciably broader than can be described by disc blackbody models even
including relativistic effects, and (2) the spectral features near 5-9 keV
commonly seen in such spectra can be well described by reprocessing of hard
X-rays by optically thick, highly ionized, relativistically moving plasma.

Astrophysics