出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：Compact object displays drastic spectral and timing changing from the beginning to the end of
an outburst, showing the different efficiencies of accretion processes. Black hole binaries hence
exhibit schematically two different states in X-ray spectra: the first dominated by a thermal component
and the second by a hard powerlaw shape like. Whereas the hard component is often
attributed to the emission of a radiatively inefficient corona, the thermal component is interpreted
as the emission of the optically thick accretion disc.
The commonly accepted picture suggests that the observed transition between hard and soft states
is associated by a drop in the accretion efficiency of the thermal component by a recession of the
internal disc radius in hard states. However, recent studies based on relativistically broadened iron
line and the thermal component strength analysis would tend to show the presence of the disc in
the vicinity of the horizon. By a reanalysis of archive spectra where thermal emission is present,
we tracked the values of the disc radii during outbursts among several sources. Indeed, whereas a
constant inner radius would imply that the disc luminosity should monotonically depends on the
temperature, we show that this relationship seems to deviate at the lowest luminosities.
