Mapping the inner accretion disc of the Galactic black hole J1550–564 through its rise to outburst

We study the spectral properties of the first 14 observations of the rise to outburst phase of the X-ray transient J1550–564. Using both the PCA and HEXTE instruments, we find that the 3–200 keV spectra pass smoothly from a standard low/hard state to a very high state. The classic high state is never encountered, possibly indicating that it is not a phenomenon of the rise phase. We find that the individual PCA spectra can be fitted adequately …